The Owls 2000 confernence was a great success and we anticipate the release of proceedings for the conference in the next few weeks. The final program for the conference is reproduced below.
Program Australian National Wildlife Collection Tours – Friday 21 January 2000 Free guided tours of the Australian National Wildlife Collection at CSIRO Division of Wildlife and Ecology, will be offered to delegates during the conference. Dr Richard Schodde will be your guide of this extensive and important scientific resource. Please check at the Registration Desk to register for these tours. Visit to Tidbinbilla & Namadgi - Friday 21 January 2000 Tidbinbilla Nature Reserve in the Australian Capital Territory is 5,500 hectares and a 40-minute drive southwest of Canberra. The vegetation ranges from open grassland to wet and dry eucalypt forest, and fern gullies, to sub-alpine heath. Tidbinbilla has a number of interesting loop trails to walk, and interesting fauna, including, Satin Bowerbirds, Superb Lyrebirds, cockatoos, rosellas, Platypus, kangaroos, Emus, and occasionally, Powerful Owls. Tidbinbilla has breeding programmes in large semi-wild enclosures for a number of waterfowl species, Koalas, and Brush-tailed Rock Wallabies. Adjoining Tidbinbilla Nature Reserve is Namadgi National Park, at 106,000 hectares, the northern most alpine environment in Australia The vegetation ranges from open grassland at 600 metres to wet and dry eucalypt forest, and fern gullies, to subalpine heath at 1911 metres. Namadgi National Park comprises 48% of the Australian Capital Territory, has many bird species, and a number of interesting walks, including one to Aboriginal rock paintings. Cost: $40pp Visit to Kosciuszko National Park – Friday 21 January 2000 Kosciuszko National Park is a 600,000 hectare park 2.5 hours drive south of Canberra in New South Wales. At 2228m Mount Kosciuszko is the highest point in Australia, and contains the major assemblage of alpine vegetation on the Australian mainland. We will take a chair lift from the village of Thredbo and, from the top of the lift, participate in a ranger-led 12km walk, up to and back from, the summit of Mount Kosciuszko (4 hours). A moderate level of fitness is required to complete the walk. The whole track is above the tree line and relatively easy walking. An alternative, easier walk, to the Kosciuszko Lookout (4km return), will also be offered. Average daily summer temperatures are between 14 and 24 degrees Celsius. Cost: $70pp Post conference Tours - Owls Study Tour to south-eastern New South Wales and north-eastern Victoria – Monday 24 to Thursday 27 January 2000 This tour is designed to visit the regions where most research on large forest owls has been conducted in Australia. We will attempt to observe the Powerful Owl, Sooty Owl, Masked Owl and Barking Owl, and several of their principal prey species. We will also observe and discuss the state of biological knowledge on these owls, current research directions and the responses by management agencies to conserve these species. A wide range of environments will be visited, from the heavily-forested coastal regions, through alpine areas and mountain ranges to the highly-fragmented woodlands of the inland western slopes. The tour will depart Canberra on Monday morning 24 January, travel to and overnight in Eden (NSW). Tuesday night will be in Orbost (Victoria), Wednesday night in Beechworth (Victoria), returning to Canberra by late afternoon on Thursday 27 January. Cost: $400pp - Single Supplement - $70 Please note:
Posters
Comparative habitat use by Owls in a high altitude (1700 – 3000 m) Rocky Mountain forest
Between 1992 and 1994 we surveyed owls in the Grey’s River Watershed on the Bridger Teton National Forest Wyoming, U.S.A. This rugged area, composed primarily of conifers, is inaccessible between November and February due to snow cover. Six principal species of owls were heard and seen between March and June. They were: Great Horned Owl, (Bubo virginianus); Northern Pigmy Owl, (Glaucidum gnoma); Great Gray Owl, (Strix nebulosa); Long-eared Owl (Asio otus); Boreal Owl (Aegolius funereus), Northern Saw-whet Owl (Aegolius acadicus). By using a geographic information system, and habitat variables collected on site, we were able to identify macro and microhabitat characteristics at owl use sites. Boreal Owls were found in structurally complex Engelmann spruce/subalpine fir (Picea engelmannii/Abie lasiocarpa) habitats; however the mean stand size in which Boreal Owls were found was 538 ha while Long-eared Owl stand size was 111 ha. Additional, Boreal Owls were never found within 100 m of a road, whereas, Long-eared Owls were often heard within the narrow forest stands that paralleled roads and watercourses of the study area. Great Gray Owls and Great Horned Owls used lodgepole pine (Pinus contorte) habitats. Great Gray Owl average stand size was only 75 ha, and vocalizing owls were often in close proximity to large wet meadows. Great Horned Owls were found at the base of slopes in larger lodgepole stands, but in close proximity to both wet meadow and open sagebrush habitats. Northern Saw-whet Owls preferred stands dominated by quaking aspen (Populus tremuloidas) and avoided areas near clearcuts. Northern Pygmy Owls were found in areas with larger and taller trees relative to availability. Our results showed how the six owl species used different habitat types within the study area and how habitat alterations affected the species. Wednesday 19 January – 14.50 to 15.10
On the New Mexico State University (NMSU) campus, most male and a few female burrowing owls overwinter at burrows they used for breeding the previous Spring. All fledglings leave the area. Therefore, the southern New Mexico population is partially migratory. Overwintering pairs are the first to begin nesting the following Spring. There is a low frequency of return of previously-banded migrant owls. Some owls return after an absence of several years. Some migrant females return to their mates of the previous year and some visit several males before settling with one. Females who choose new mates prefer males who have longer-duration primary calls. Females with prior breeding experience in the study area do not arrive significantly earlier than females without area experience. Resident males produce more nestlings (mean = 3.5 ± 2.6) than migrant males (mean = 2.5 ± 1.9) and area-experienced females produce more nestlings (mean = 3.6 ± 2.4) than area-inexperienced females (mean = 2.2 ± 2.3). Resident males paired with area-experienced females produce more nestlings than any other pair type. The overall population size on the NMSU campus has declined since 1995, despite no loss of habitat. The culprits seem to be rock squirrels (Spermophilus variegatus), which displace owls from their burrows and may eat owl eggs . Thursday 20 January – 12.10 to 12.30
Four hundred and twenty three incidental site records (including 26 nesting records and 40 roosting records) were compiled and used to investigate the distribution, abundance and habitat preference of the Tasmanian masked owl, an endemic subspecies. This study was supplemented with a systematic survey of owls across forest types in Tasmania. The survey used the broadcast of pre-recorded calls to elicit call responses. Detection rates using playback of pre-recorded calls suggested a higher abundance of owls than indicated by incidental data and anecdotal information producing a population estimate of about 600 breeding pairs or territories. The detection rates were higher for the Tasmanian masked owl than those reported for its southern mainland counterpart in superficially similar habitats. Approximately 94% of the preferred habitat of the Tasmanian masked owl is unreserved and most is private land. Much of this habitat has been fragmented by agriculture. This habitat may favour owls by increasing the size of open foraging areas, particularly improved pasture, and the associated increase in the abundance of introduced prey species such as the European rabbit. The availability of large hollows for nesting does not appear to limit population size or density at present, however, continued fragmentation of forest remnants and pasture trees through clearing and/or natural attrition may have a significant impact on these parameters over the next decade. Wednesday 19 January – 13.50 to 14.10 Forest Owl management in north central New South Wales:
Large forest owls have been surveyed in a standard manner across two large forest management areas in the past three years, and two different approaches to owl management in logging areas have been taken. This paper reports on the results of those surveys and management actions. Owls were detected across the forested landscape in the region. Management prescriptions based on reservation of a standard area (300 ha) per detection were implemented in some sites. In other areas, where it was assumed that owls occurred across all sites, standard reservation of owl habitat were implemented arcos the landscape. In the latter approach, 25% of the area in the landscape (5 000 to 10 000 ha) was retained for owl management. Strengths and weaknesses of the two approaches are discussed, but in general it appears that a landscape approach has the most benefit for multiple land use. Results of monitoring are reported which indicate that owl populations persist at detectable levels across both management areas. Sunday 23 January – 13.50 to 14.10 A survey of road-killed owls in north-eastern New South Wales.
All owls found dead along roads were noted as part of a larger survey of road-killed vertebrate fauna in north-eastern New South Wales. The survey began on 18 February 1978 and is on-going. Data to 18 December 1999 are presented. A total of 197 dead owls of five species, comprising two hawk owls, genus Ninox, and three masked owls, genus Tyto, were recorded. An average of 9.0/yr owls were recorded. 91.3% of all records comprised the two common species, the Barn Owl Tyto alba and Southern Boobook Ninox novaeseelandiae. Only three specimens (1.5%) of the Powerful Owl Ninox strenua, seven (3.6%) of the Masked Owl Tyto novaehollandiae and seven (3.6%) of the Grass Owl Tyto capensis were found. The seasonality of records is presented. The Barn Owl, Masked Owl and Southern Boobook were recorded throughout the year. The Grass Owl was recorded only between late winter and late spring (early August and late November) and the few Powerful Owl records were between spring to late summer. The data with respect to the Masked, Grass and Powerful Owls should be treated with caution due to the small sample sizes. The relative numbers of owls killed compared to other vertebrate species, the reasons for the seasonal bias, where present, and factors causing owls to be road-killed are discussed. Identification characters of the Tyto owls are presented. Saturday 22 January – 12.10 to 12.30
Historically the Powerful Owl has been seen as a species being restricted to, or most numerous in, dense gullies of tall open forests in hilly or mountainous areas of the coast and Great Divide. Recent research, however, has found the Powerful Owl may be more numerous and breed more successfully in a wider range of habitats than previously believed. In particular, the owls have been found living in forests and woodlands within metropolitan areas of some major cities. Here we report on the breeding success of a number of pairs of Powerful Owls in outer urban Melbourne. Study sites range from relatively undisturbed, wet sclerophyll habitat 80km from central Melbourne, through dry sclerophyll, eucalypt-dominated open forest with some disturbance to a highly disturbed urban parkland located only 18km from central Melbourne. Our results found that Powerful Owls will successfully breed in some urban areas, however, there is a limit to the amount of human disturbance Powerful Owls can apparently tolerate near their breeding hollow. In the most heavily utilized section of the urban parkland all breeding attempts were unsuccessful and we have evidence that in one year the young were eaten by one of the parents. This followed construction of a bicycle track under the nest tree during the breeding season. The Powerful Owls subsequently relocated to a more secluded breeding hollow and successfully raised two juveniles the following year. Recommendations for management of Powerful Owls in urban areas will also be discussed in the context of these results. Saturday 22 January – 14.30 to 14.50 Distribution, taxonomy, status and major threatening processes for owls of the Australasian Region
The Australasian Faunal Region, defined here as east of Wallace’s Line from Wallacea to Fiji and New Zealand, is the centre of diversity of the genera Tyto and Ninox. Coupled with the relict distribution of the other tytonid genus (Phodilus) in Africa and South-East Asia, this pattern suggests a Gondwanan origin for the Tytonidae. If Ninox is related to Ketupa (South-East Asia) and Scotopelia (Africa), then a section of the Strigidae may also have had a Gondwanan origin. Evidence suggests an endemic Australasian clade of strigid genera: Ninox (with outliers in South-East Asia and possibly Madagascar), Uroglaux (=Ninox), Sceloglaux (apparently close to Ninox), and perhaps Nesasio (whose affinities are uncertain). Otus, with several regionally endemic species, penetrates Wallacea and occurs marginally in north-western Melanesia. The occurrence of an isolated, supposedly asionine owl (Nesasio) in the Solomon Islands is zoogeographically anomalous. With the exception of the probably extinct New Zealand Laughing Owl (Sceloglaux), the regionally most threatened owl species are island endemics of tropical forest in Wallacea and Melanesia. Ninox natalis (Christmas I.) is now Critically Endangered, owing to the invasion of a predatory ant. Several species are Vulnerable: Tyto nigrobrunnea (Taliabu I.), T. aurantia (New Britain), T. manusi (Manus I.), Otus collari (Sangihe I.), O. beccarii (Biak I.), Ninox rudolfi (Sumba), Nesasio solomonensis (Solomon Is.). Several are Data-deficient: Tyto sororcula (Moluccas, Tanimbar Is.), T. inexspectata (Sulawesi), Uroglaux dimorpha (New Guinea). One is Near-threatened: Otus silvicola (Lesser Sundas). The remainder, including all Australian species, are Least Concern (= not globally threatened). However, some Australian subspecies of Tyto novaehollandiae, Ninox rufa and N. connivens are threatened, and two of N. novaeseelandiae are extinct. For most species in the region, the major threatening processes are deforestation and logging. Unresolved taxonomic problems include: species limits in the masked-owl complex (Tyto sororcula, nigrobrunnea, manusi), the sooty-owl complex, and the grass-owl complex; species limits in the Wallacean Otus complex, including the identity of an Otus on Sumba; racial affinity of south-western Ninox connivens; species limits in the Ninox boobook/novaeseelandiae and N. squamipila complexes; generic allocation of Ninox superciliaris (Madagascar); and the affinities of Sceloglaux and Nesasio. Saturday 22 January – 11.10 to 11.30
This study aimed to determine the extent of anatomical variation in the digital tendon locking mechanism (TLM) among the Strigiformidae, with particular reference to a number of Australian owl species. The digital TLM, as its name implies, is located on the main digital flexor tendons of these birds. It consists of two modified surfaces which upon digital flexion engage to provide a ratchet-type lock. The mechanism acts to maintain the distal and other inter-phalangeal joints of the digits in a flexed position, enabling a prolonged grip with little or no involvement of the flexor muscles of the leg. Variation in the size of these two modified regions, and in the size, shape and arrangement of the individual locking elements was investigated through the comparison of a range of macrostructural and microstructural measurements. Variation in the structure of the TLM between different avian orders has already been documented. However, the degree of variation within an order was previously unknown. The basic components of the TLM were very similar among the birds studied, but extensive variation in their relative size and shape was found. Structural differences between owl species were consistent with their phylogenetic separation into the Strigidae and Tytonidae families, however differing functional pressures were also considered as a possible contributing factor. Through comparison with diurnal non-strigiform raptors a degree of variation in TLM design between the two raptor groups was revealed. As well as their phylogenetic separation, selective pressures due to the differing ecological and behavioral habits of owls may explain the differences. Similarities between the two raptor groups were evident through comparison with a non-raptor out-group, suggesting that the raptorial habit has led to convergence in TLM design. Wednesday 19 January – from 16.00 to 16.20 The owls in the Neotropics: a brief review
Most of the owl species in the world are distributed in the tropical regions. In the Neotropical region there are 64 species of owls, these species represented 32.5% of the total species around the world. In the Neotropics, there are 13 genera of owls; five of them are endemic for that region. Genera more representatives are Otus (23 species), Glaucidium (14 species) and Strix (9 species). The 39% of those species have an endemic or subendemic distribution in the Neotropical region. Although tropical owls are among tropical birds species more endangered, knowledge about their ecology and biology of many species is limited. In this brief review, we present the general situation about the Neotropical owls related to their knowledge and different aspects as taxonomic controversies to classify them to human related problems that are determining their survival. Saturday 22 January – 11.30 to 11.50
Research on the spotted owl began rather inauspiciously in the early 1970's, and has exploded into a very extensive effort involving many different researchers and hundreds of field technicians at many different research institutions scattered around the United States. As research has proliferated, it has become increasingly obvious that relationships between spotted owls and their habitat are not nearly as simple as was once thought. In addition, the infusion of new researchers and new methods of population analysis has resulted in a rapid expansion of our knowledge, and not infrequent disagreements regarding the interpretation of data and the most appropriate methods for conducting field studies and data analysis. Management recommendations for spotted owls have typically involved the protection of extensive networks of old forest reserves, or protection of particular kinds of forest within the general landscape. The development of large scale reserve systems for spotted owls and other species that prefer old forests, has led to considerable research and development of mathematical models for assessing and predicting the behavior of populations. These models typically involve a set of assumptions regarding dispersal behavior of young owls, as well as assumptions about the number of resident owls that are likely to be present in a given area. Typically, these models assume an inverse relationship between survival rates of owls and the amount of suitable habitat that is present within a hypothetical home range. The most important factor influencing population persistence in these models is adult survival. However, juvenile survival rates and dispersal behaviour are crucial elements in models and can greatly influence population performance. Recent studies of juvenile dispersal suggest that dispersal patterns are highly variable and differ substantially between males and females. Incorporating these kinds of variability into future models will be of interest. Although mathematical and spatial models have become increasingly common in our studies, we should never forget that these models cannot be trusted to accurately predict outcomes. However, they are very useful for comparing the relative performance or behavior of populations in different kinds of landscapes. One factor that is virtually impossible to incorporate into models of population performance is the influence of invading exotics. In the western U. S., the barred owl is gradually invading the range of the spotted owl. As this occurs, there is increasing evidence that barred owls are displacing or hybridizing with spotted owls, or even killing spotted owls. This is making it increasingly difficult to interpret data from our spotted owl studies, because our observations are frequently confounded by barred owls. Sunday 23 January – 9.00 to 9.50 Natal and Post-natal Dispersal of Northern Spotted Owls
We studied the behavior of 1,475 northern spotted owls (Strix occidentalis caurina) that dispersed during banding and radio-telemetry studies in Oregon and Washington in 1985-1996. The sample included 324 radio-marked juveniles, and 1,151 banded individuals (711 juveniles, 440 non-juveniles) that were recaptured or resighted after dispersing from the initial banding location. Dispersal was typically initiated with a series of rapid movements away from the natal site during the first few days or weeks of dispersal. Thereafter, most juveniles settled into temporary home ranges in late October or November, and remained there for several months. Then, in February-April there was a second surge of dispersal, with many owls moving considerable distances before settling again in their second summer. Subsequent dispersal patterns were highly variable, with some birds settling permanently in their second summer, and others occupying a series of temporary home ranges before eventually settling on territories when they were 2-5 years old. On average, females dispersed farther than males. Differences between dispersal distances of radio-marked and banded owls were so small that we considered them biologically insignificant. Maximum and final dispersal distances were largely independent of the number of days that juveniles were tracked. A minimum of 6% of the banded, non-juvenile owls on our study areas changed territories each year. The likelihood of post-natal dispersal was higher for females, young owls (1-2 yrs old), owls that did not have a mate in the previous year, and owls that lost their mate from the previous year through death or divorce. Mean distances moved by post-natal dispersers were shorter than distances moved by natal dispersers, and did not differ between the sexes or study areas. One-and 2-year-old owls tended to disperse farther than owls that were >2 years old. The direction of post-natal dispersal did not differ from random. Our data fit the general pattern observed in birds in that females dispersed farther than males and that dispersal distances were negatively skewed towards short distance dispersers. Our comparison of data from radio-marked and banded owls demonstrates that the negatively skewed distribution of dispersal distances represents the actual distribution of dispersal distances, i.e., is not the result of small study area bias on recaptures of banded owls. Our findings were similar to other studies of birds in that there appeared to be little correlation between dispersal distance and individual reproductive rates, at least as measured by age at first breeding. Although females tended to disperse farther than males, the distributions of male and female dispersal distances overlapped broadly, suggesting that sex-biased dispersal was not a particularly effective method for reducing the likelihood of close inbreeding. Thursday 20 January – 11.30 to 11.50
Taphonomic analysis of pellets collected from the Barn Owl (Tyto alba), Southern Boobook (Ninox novaeseelandiae), and the Tasmanian Masked Owl (Tyto novaehollandiae castanops) was conducted as part of an honours project during 1999. All three species of owl were feed a known diet of house mice (Mus musculus) and their pellets collected daily. Taphonomic analysis of their pellets was carried out to establish, firstly if a signature criteria of owl cast bone can be developed and, secondly, to determine if there is a difference in the degree of digestion and skeletal element composition in the bone from the pellets of the three owl species. Analysis of skeletal fragmentation and the percentage of bones recovered as compared to the expected were performed. The results of this taphonomic study was compared to the small vertebrate fauna excavated from the archaeological site Derwent River Shelter Number 7 (DRS7), Tasmania, because the small faunal elements are assumed to have been accumulated by owls. Pellets from Tyto alba, Ninox novaeseelandiae and Tyto novaehollandiae castanops were examined as these are the only species currently known to have lived in Tasmania during the Late Holocene. Within the rockshelter two square columns were excavated, with six stratigraphic units being identified. The bottom unit is thought to have accumulated prior to Aboriginal occupation of the shelter, the middle four units during Aboriginal occupation, and the top unit during European arrival and settlement of Tasmania. There is one radiocarbon date available from below the sixth unit, indicating that the skeletal material has accumulated during the past 3000 years. Analysis of the small fauna excavated from DRS7 will allow the spectrum of the dietary patterns of the owls to be established. Wednesday 19 January – 11.50 to 12.10 Large Forest Owl conservation in East Gippsland, Victoria
The East Gippsland Forest Management Area is a heavily forested region of 1.2 million hectares, comprising 640,000 ha of state forest, 400,000 ha of national park and the balance private property. Timber production is a major activity in state forest. The region supports substantial populations of three large forest owls, the Powerful (Ninox strenua), Sooty (Tyto tenebricosa) and Masked (Tyto novaehollandiae). All are threatened in Victoria and are regarded as sensitive to intensive timber harvesting. In 1995 the government produced a management plan for the state forest in East Gippsland, which aims to balance conservation and timber production. The presence of large forest owls played a major role in selecting conservation areas within state forest. The large forest owl conservation strategy involved gathering all existing records, conducting additional surveys to fill in gaps, developing a model of preferred owl habitat, conducting preliminary Population Viability Analysis and negotiating a process by which a substantial population of owls would be protected in reserves which met criteria for size and habitat quality. A key part of the process was the negotiation of the target number of pairs for protection. In the absence (at that time) of good information on the population of owls across the rest of Victoria, we sought to provide secure habitat for 100 pairs of each species in the region. This target has subsequently been refined through additional survey and improved PVA, but is not substantially different. The conservation prescription for each species requires that between 500 and 800 ha be protected for each pair. Protected areas include conventional reserves and a number of Special Management Areas (SMA’s), where modified timber harvesting is permitted. Monitoring of the response of the resident owls in selected SMA’s has commenced. This owl conservation process has been adopted and refined for application to other Forest Management Areas across Victoria. Sunday 23 January – 14.10 to 14.30
This paper is a popular introduction to Australia’s ten species of owls, including the Christmas Island Hawk Owl Ninox natalis. A series of slides showing portraits, flight, hunting, habitat and nests of each species will be shown, together with pictures of the young and eggs. The commentary which accompanies and expands on the slides is from the perspective of the field ornithologist: accurate but, at the same time, anecdotal. The slides are based on photographs taken by the presenter for the book "Birds of the Night", Reed Books, Sydney 1991, but include many new shots added since then. Wednesday 19 January – 9.50 to 10.40
The owl species common to Manitoba’s forests respond differently to variations in their environment. This variation most notably comes in the form of forest fragmentation due to forestry and agricultural clearing in the western upland region of Manitoba known as the Manitoba Escarpment. Variation in slope is also a possible factor influencing owl distribution in this area.. The preliminary results of a use versus availability analysis with regards to habitat and slope characteristics are presented in this paper. Locations for great horned owls (Bubo virginianus), great gray owls (Strix nebulosa), barred owls (S. varia), northern saw-whet owls (Aegolius acadius), boreal owls (A. funereus) and long-eared owls (Asio otus) were obtained through nocturnal surveys run from 15 March 1999 to 4 June 1999 and by incidental occurrences during the breeding season. These locations were computerized as GIS thematic layers, with regards to species and overlayed on digital forest resource inventory maps of the study area. These were used to generate data regarding stand type, age, degree of fragmentation and connectivity and slope characteristics. Owl location data was compared with that associated with random sites in a use versus availability analysis. Comparisons will be made between species with regards to habitat use and the application of the results of this study in regards to owl and forest management in Manitoba will also be discussed. Sunday 23 January – 11.50 to 12.10 Ecology of the Forest Owlet Athene blewitti
The forest owlet (Athene blewitti) is one of the least-known endemic birds of India. It was rediscovered after 113 years in November 1997 by Rasmussen and her colleagues (King & Rasmussen, 1998) in a dry deciduous forest of Maharashtra. There is very little information available on the status, distribution, vocalization, feeding habits and breeding season (Ali & Ripley, 1987). In 1880’s seven specimens of the forest owlet were collected (Rasmussen & Collar, 1998) in India. We conducted one year study (June 1998-May 1999) to understand the current status, distribution and ecology of the species in collaboration with the Smithsonian Institution. The calls recorded during earlier surveys from the rediscovered site were played back to locate more birds at other sites. Total seven pairs were located at two different locations in the tropical deciduous forest, between 400-500 m of elevation. Of these seven pairs, three pairs were found nesting from October onwards and one pair re-nested in the same breeding season. Most of the sightings of the forest owlets are restricted to teak Tectona grandis forest with mixed tree species such as Boswellia serrata, Lagerstroemia parvifolia, Dalbergia latifolia, interspersed with grass species like Cymbopogon maritni, and Sehima nervosum. The perching height ranges between 9-12 m (n=200) while feeding height ranges between 3-4 m (n=100). The adults were observed caching food in dead hollow trunks of diameter 72.3±0.57 cm and depth of 105±90.9 cm (n=3). There was morphological as well as behavioural dimorphism between male and female forest owlet. Being a diurnal and crepuscular species, most of the data on the feeding behaviour were collected by direct observations (n=183) and the diet mainly consisted of field mice (11.50%), rat (0.5% ), birds (such as warbler, quails) (2.8%), skink (53.4%), snake (0.5%), frog (1.6 %) and grasshopper (1.7%). It is difficult to quantify preferences for food species between the male and the female as most of the observations were collected in the breeding season and the female totally depends on the male for food during nesting period. Major threats observed were habitat degaradation/alteration for cultivation, encroachment for settlements leading to fragmentation of habitat thus making the species more vulnerable.
Wednesday 19 January – 14.10 to 14.30
The three large forest owls of south-eastern Australia, the Powerful Owl (Ninox strenua), Sooty Owl (Tyto tenebricosa) and the Masked Owl (T. novaehollandiae), are wide-ranging, naturally uncommon species whose conservation requirements are unlikely to be met wholly within a system of formal nature conservation reserves. Until recently, little was known about the distribution, abundance and habitat requirements of these owls, and the extent to which wood production forestry may be compatible with their conservation. All three species are listed as "vulnerable" under the NSW Threatened Species Conservation Act 1995. Research over the past 10 years has indicated that these owls are more abundant and evenly distributed throughout their ranges in NSW than thought previously. The Sooty Owl has the most restricted distribution, being confined to rainforest and the wetter eucalypt forest types near the coast and adjacent mountain ranges, whereas the Powerful Owl and the Masked Owl also occur among the drier forest types. The Masked Owl is the least common in forested environments. Regional surveys showed little evidence for a decline in owl numbers in a mosaic of logged and unlogged forest. The Powerful Owl and Sooty Owl were recorded commonly in logged landscapes but the home-ranges for these birds were centred upon significant areas of unlogged or less disturbed forest in riparian areas. These areas were used for nesting and roosting by the owls, and also were preferred foraging areas. The Masked Owl appeared to have a closer association with unlogged or selectively-logged forests, particularly those having an open understorey and a sparse ground cover. Forests on private land that were highly fragmented and degraded by agricultural practices appeared to make little contribution to regional conservation of large forest owls. The management procedures in place for large forest owls in wood production forests will be discussed. Sunday 23 January – 9.50 to 10.40
Multiple surveys (1988-89, 1992, 1994 and 1997) in young regrowth eucalypt forest provided some insights into the temporal, as well as the spatial, dimension of owl population recovery following disturbance caused by intensive logging (in the early-mid 1970’s) and wildfire (in 1972 and 1980). By 1994, and confirmed in 1997, surveys recorded increasing numbers of several important prey species for the Powerful Owl (Ninox strenua) and the Sooty Owl (Tyto tenebricosa), and this was matched by significant increases in the distribution and abundance of these two owls. Radio-tracking studies showed that the home-ranges of these owls were centred upon limited areas of unlogged forest which provided their core habitat needs (e.g. nest trees, favoured roosting locations) and the owls foraged extensively among the surrounding regrowth forests. The absence of the Masked Owl (T. novaehollandiae) to date may be due to the dense forest structure typical of young regrowth forests which may inhibit the foraging behaviour of this species. Sunday 23 January – 14.50 to 15.10
This paper presents results from the first of a three year study into the species in north east Victoria, whose aims are to develop habitat models for the species and formulate the management guidelines. The study area includes approximately 750 km2 of low altitude, fragment Box-Stringybark woodlands with adjacent farmland between Chiltern and Beechworth (36 14 00, 146 40 00) and 25 km of riverine habitat with fragmented River Red Gum Eucalyptus camaldulensis forest. Twenty pairs have been located in the Box Stringybark habitat and three in the River Red Gum Forests. Nest sites were located for 16 and three pairs respectively in the two habitats. Breeding sites were in hollows in Long Leaf Box E. nortonii, Red Box E. polyanthemos, Blakely’s River Red Gum E. blakelyi, and River Red Gum. In the Box-Stringybark habitat all but one nest was within 0.5 km of the woodland edge. The surrounding areas were predominantly grazing land. The mean nearest neighbour distance between nests was 3.1 km. To date a single female has been radio-tracked for five months. Almost all of her hunting has been in edge habitats within 1.5 km of the activity centre. The diet of 10 pairs has been examined form prey remains around their nests. This has shown a highly diverse diet, including many edge species and some open country species including Magpie Gymnorhina tibicen, Raven Corvus coronoides, White-winged Chough Corcorax melanorhmphos, Eastern Rosella Platycercus eximius, Eurasian Coot Fulica atra, Twany Frogmouths Podargus strigoides, Grebe species and European Rabbit Oryctolagus cuniculus. Numerically the latter seems to be the most important prey at most sites. Future work will involve determining home range sizes, habitat selection and diet, from which detailed habitat models for the species will be developed. Wednesday 19 January – 14.30 to 14.50
Defenses against parasites and pathogens are expected to be costly, and hence beneficial only when needed. We studied the assumptions of benefits and costs of defense against blood parasites with Tengmalm's owls (Aegolius funereus) and Eurasian kestrels (Falco tinnunculus) breeding in western Finland. These birds of prey feed mainly on voles, whose population densities fluctuate in a cyclic manner with 3-4 years between successive peaks. First, we found that blood parasite infections (intracellular Haemoproteus spp., Leucocytozoon spp. and extracellular Trypanosoma spp.) were more prevalent in poor food years. Second, we found that successful defense against blood parasites may be beneficial, as seen in the reduced clutch size of female owls infected with leucocytozoids, and later start of laying in kestrel females mated with haemoproteid infected males. Moreover, trypanosome-infected male owls defended their offspring less vigorously than uninfected males. Third, with supplementary food experiments and brood size manipulations we showed that defending against blood parasites is costly, and that the costs may be modified by environmental conditions, and that the expected costs can vary between the sexes due to their different parental roles. The prevalence of trypanosomes among female owls was lower in food supplemented nests than in control nests, whereas in female kestrels food supplements reduced trypanosome and haemoproteid prevalences only in a year of low natural food supply. Manipulations of kestrel brood size revealed that trypanosome prevalence in males increased with experimental brood size, and the difference in prevalences between reduced and enlarged broods increased with decreasing natural food supply. In summary, these results support the idea of phenotypic costs of defense, and ultimately, may help in explaining why the appearance of reproductive costs may be associated with sex of the host and with variation in environmental conditions. Saturday 22 January – 9.00 to 9.50 Modelling distributions of large forest owls, as a conservation tool in forest management.
Large owls are top predators in Australian forests, with large home ranges. They and some of their prey need old hollow-bearing trees. Hence selected forest stands need to be retained to conserve large owls in managed forests. To help select such stands, owls were surveyed at 2000 sites, using call playback and spotlighting. Results from 472 sites in north-east Victoria were modelled by logistic regression with respect to habitat and context variables. Powerful Owls (Ninox strenua) favoured dry or riparian forest with abundant hollow-bearing trees, Blackwood wattle trees (Acacia melanoxylon), diverse vegetation types and extensive mature forest within 5km. Sooty Owls (Tyto tenebricosa) favoured wetter and more senescent forest, with abundant tree-ferns and Silver Wattles (Acacia dealbata). Both species favoured sites with abundant arboreal mammals, but there was little overlap. Barking Owls (Ninox connivens) and Masked Owls (Tyto novaehollandiae) were rare. Field tests of the models showed that Powerful and Sooty Owls were substantially more likely to be found at sites of high than low predicted probability of occurrence. Geographical Information Systems were used to map predicted habitats and help select Special Protection Zones for large owls (160 locations in north-east Victoria, 500 ha each). Field records were given priority in selecting these zones. Similar work is under way for southern Victoria. Sunday 23 January – 11.10 to 11.30 Racumin rodenticide – potential environmental impact on birds
Over the past 40 years, first generation, multiple dose rodenticides have been used to successfully control rats and mice. In that time there have been few, if any, incidents reported of secondary poisoning of wildlife. In more recent times, secondary poisoning of wildlife has become an issue since the development of the second generation, single dose rodenticides. There are two main groups of rodenticides: acute poisons such as zinc phosphide, which kill rodents within hours of ingestion; and chronic poisons. Acute poisons have fallen out of favour due to bait shyness. Chronic poisons have delayed actions which reduce the risk of bait shyness. The anticoagulants are the principal type of chronic poison used now. Vitamin K assists in the clotting of blood. Anticoagulants act to overwhelm production of Vitamin K in the rodent’s body, reducing the rodent’s blood clotting ability. If the rodent has eaten sufficient bait it will die from internal bleeding 3 to 8 days after the initial feed. Racumin, containing coumatetralyl, is a first generation, multiple dose bait. Multiple dose means that the rodent must feed on the bait at least three times to ingest a lethal dose. Single dose baits require only one feed but in practice rodents consume bait over several days resulting in higher residue levels in the body which may increase the risk of secondary poisoning. Racumin has seen renewed interest in recent years owing to the lack of secondary poisoning incidents associated with its use. Studies indicate that Racumin carries a lower risk of secondary poisoning. This has led to Racumin being used in environmentally sensitive situations such as the Galapagos Islands and Norfolk Island. Continued monitoring and further studies are being carried out to confirm the reduced risk to wildlife from using Racumin. Saturday 22 January – 14.10 to 14.30
Throughout human history, owls have variously symbolized dread, knowledge, wisdom, and death. In most Western cultures, views of owls have changed drastically over time. Owls can serve simultaneously as indicators of scarce native habitats and of local cultural and religious beliefs. Understanding historical and current ways in which owls are viewed, and not imposing Western scientific views on other cultures, is an important and necessary context for crafting conservation approaches palatable to local peoples. Wednesday 19 January – 12.10 to 12.30
The southern boobook (Ninox novaeseelandiae) is the most common and widespread owl in Australasia. Relatively little has been published on the owl’s diet in mainland Australia. Early studies suggested that they fed mainly on small animals up to the size of house mouse (Mus musculus). More recent reports have shown them to take a wider range of prey including invertebrates, amphibians, reptiles, birds and mammals up to the size of rock dove (Columba livia) and juvenile common ringtail possum (Pseudocheirus peregrinus). This paper reviews these studies briefly and presents new data, based on analysis of regurgitated pellets and field observations in southern Victoria. These data show that southern boobooks prey opportunistically on a wide range of small to medium sized mammals and birds, and invertebrates. Some uncommon mammal species were found in pellets. Field observations are described of southern boobooks taking a sub-adult common ringtail possum, and attempting to take a Leadbeater’s possum (Gymnobelideus leadbeateri). Interspecific conflict with a barn owl (Tyto alba) is also described. Thursday 20 January – 13.50 to 14.10
A study of the distribution and ecology of the Sooty Owl Tyto tenebricosa in Mountain Ash Eucalyptus regnans forests of the Victorian Central Highlands examined whether its distribution was influenced by the occurrence of stands of different age classes. It also provided information on the potential role of the Sooty Owl as an indicator of the presence of specialised mammal species and habitat quality. The Sooty Owl was surveyed at 130 sites stratified across four age classes of unlogged forest, representing different stages of regrowth after wildfire. The age classes varied from young stands dominated by 50 year old trees to old-growth stands dominated by trees exceeding 250 years of age. Detailed habitat data were collected at each site and ecological information was obtained from four Sooty Owl territories in the survey area. Additional information was obtained from historical records. Systematic surveys resulted in records of Sooty Owls at 22 sites, and 4 other species of nocturnal birds and 7 species of scansorial and arboreal marsupials were also recorded. An analysis of survey results showed that the Sooty Owl was evenly distributed throughout the study area’s 280-1250 m elevational range. More records were obtained from gullies than slopes or ridges, but records from gullies comprised less than half the total. Historical records from some sites suggested occupation for periods of from 5 to 10 years. Twenty-four territories were estimated to occur in the Mountain Ash forests of the study area, indicating a density of one pair per 16 km2. The few Sooty Owl roost and nest sites found were all in trees with a dbh greater than 2.2 m. The probability of finding a Sooty Owl at a site was modelled using habitat variables considered likely to influence its distribution. The chance of finding the species was found to increase with an increase in the amount of old-growth forest, but decreased with an increase in the percentage of trees with dead-tops. This suggests that large patches of old-growth forest provide optimum habitat for the Sooty Owl in Mountain Ash forests and that other old-growth attributes as well as high densities of hollow-bearing trees may be important in determining its distribution. Although the Sooty Owl is an opportunistic predator, its apparent requirement for areas of high prey species diversity and abundance suggests that it could perform well as an indicator of the presence of specialised vertebrates and high biodiversity in Mountain Ash forests. Its long-term conservation in these forests will probably depend on maintaining large patches of old-growth forest in core areas and other large areas with a high proportion of old-growth elements throughout the landscape. Sunday 23 January – 14.30 to 14.50 The population ecology of the northern hemisphere owls
This paper is concerned mainly with the contribution made by studies on owls to our understanding of the population ecology of birds. Because many northern owls feed on cyclic rodents, they face a greatly fluctuating food-supply, which influences every aspect of their ecology, from movements to survival and breeding success. Different species react to a fluctuating food-supply in different ways, but all clearly show the role of food-supply in limiting numbers and individual performance. The role of nest-sites, pesticides and other factors in limiting northern hemisphere owl numbers will also be discussed. Wednesday 19 January – 9.00 to 9.50 Rodenticide effects on British Barn Owls
The fact that rats and mice in many parts of the world have become genetically resistant to warfarin and other 'first generation' rodenticides has stimulated chemical companies to develop new 'second generation' compounds for use in rodent control. The new compounds are more toxic and more persistent than the old ones, with the potential to cause secondary poisoning in rodent predators. This paper will describe a programme to monitor the levels of rodenticides in Barn Owls in Britain, and assess the effects on populations. Saturday 22 January – 13.50 to 14.10
Consideration of the probability of the evolutionary origin of various anatomical similarities and dissimilarities in the outer ear leads to the conclusion that ear asymmetry has evolved independently in at least five separate phyletic lines among owls, represented by the following respective genera: 1. Tyto, 2. Phodilus, 3. Bubo, Ciccaba, Strix, 4. Rhinoptynx, Asio, Pseudoscops, and 5. Aegolius. The group comprised of Bubo, Ciccaba and Strix may represent more than one line of origin of ear asymmetry. Ear asymmetry in owls makes the auditory directional sensitivity pattern different in elevation – in the vertical plane – between the two ears for high frequencies, and thereby makes possible localization of sound in the vertical plane, based on comparison of intensity and spectral composition of sound in the two ears. When an owl localizes prey by hearing, the direction of the sound source usually forms a shallow angle with the ground. Therefore, a given angle of error converts into a longer distance off the target along the ground for a vertical angular error than for a horizontal angular erro. This is a crucial factor that selects for good vertical localization ability of owls which depend strongly on hearing for localization of prey. Selection pressure for good ability to localize sound in elevation seems to lie behind the evolution of all types of ear asymmetry in owls. Habitat selection, ecological settings, prey choice, and hunting behaviour govern the selection pressures set up for ear asymmetry to originate. Differences in these respects explain the strong differences between different geographical latitudes in the proportion of species of local owl faunas that have asymmetrical ears. Wednesday 19 January – 15.40 to 16.00
Three adjacent nesting territories of Southern Boobooks (Ninox novaeseelandiae) were studied from October 1996 to October 1999. Observations were made several nights per week from just before the birds left their day roost each evening until one hr after they left their day roost. During the 529 observations we attempted to identify the ten main calls used by adults as described in a recent review of the literature: 1) boobook call, 2) single hoot, 3) por call (croak), 4) squeal, 5) bray, 6) trill, 7) yelp, 8) growl, 9) scream, and, 10) squeak. We investigated the relationship between these calls and 1) moon phase, 2) moon visibility 3) temperature, 4) cloud cover, 5) wind speed, 6) wind direction, 7) rain, 8) season. Where possible we determined whether the calling birds were male or female, and classified the boobook calls as contact, or territorial advertisement. Both sexes used most calls, though there were individual differences, and different authors may label the same calls differently. We thought that females gave the mating squeal, and males were not seen giving the bray call, though both sexes gave a quieter ‘purr' call. Thursday 20 January – 14.10 to 14.30 Do Southern Boobooks (Ninox novaeseelandiae) Duet?
A number of writers state that duetting occurs between male and female Southern Boobooks (Ninox novaeseelandiae) though this has been questioned. A recent review of the species concluded that duetting does occur based on i) observations of captives, ii) a report by Whitlock in 1923, iii) an unsourced claim that Southern Boobooks in New Zealand appear to duet. We examine definitions of duetting, and provide a simple classification system of simultaneous vocalisations to be trialed. We could find no convincing evidence in the literature, or in a study of three pairs of Southern Boobooks observed over 529 nights in and near Aranda Bushland in Canberra, that Southern Boobooks duet. Thursday 20 January – 14.50 to 15.10
The Norfolk Island Boobook Ninox novaeseelandiae undulata is confined to the small, isolated Norfolk Island Group, an Australian territory. In 1986 only one owl, a female, survived. A severe shortage of large trees with holes suitable for nesting appeared to be the immediate problem. Environment Australia, islanders and New Zealand wildlife authorities co-operated in an attempt to re-establish an Owl population in situ. Nest boxes were erected in trees in the area frequented by the female and were used readily as roosts. In September 1987, two male New Zealand Moreporks Ninox novaeseelandiae novaeseelandiae were introduced. The female paired with one male and produced four hybrid F1 offspring (in 1989 and 1990). Third generation pairs are now breeding and the population is estimated to be about 25. At present, the population appears to be characterised by late age at maturity, low breeding success and high rates of survival and recruitment. The recovery effort is low-cost, requires relatively little man-power, is carried out with minimal disturbance to the Owls, and goes hand in hand with programmes to control introduced cats, rats, birds, bees and plants. Such in situ management is not without its problems, but has great advantages, particularly in an island situation. Saturday 22 January – 14.50 to 15.10 Research and management priorities for owls in Victoria
A considerable body of research has been conducted on owls in Victoria over the last decade, and it is timely to consider research and management priorities for the future. Six owl species occur regularly in Victoria. The Barn Owl (Tyto alba) and Southern Boobook (Ninox novaeseelandiae) are currently not classified as threatened (NRE 1999), but are known to be adversely affected by agricultural intensification and timber harvesting. Research and monitoring in relation to these potential threats is a priority for these species. The Sooty Owl (T. tenebricosa) is classified as vulnerable, while Powerful Owl (N. strenua) and Masked Owl (T. novaehollandiae) are classified as endangered (NRE 1999). Management arrangements have recently been established for these three species in their strongholds in mountain, foothill and coastal forests. Monitoring and research to assess the efficacy of these arrangements is consequently a high priority. This is particularly so for the Sooty Owl, which is not found outside these forests and may be susceptible to fragmentation effects. Research and management are also needed to ensure that the sparsely distributed populations of Powerful and Masked Owls in drier inland forests and woodlands do not decline. The sixth species, the Barking Owl (N. connivens) is also classified as endangered (NRE 1999) and is the most threatened owl in Victoria, with a population comprising less than 200 pairs. Protection of habitat in key areas, surveys in some regions where its occurrence is poorly known, and research to identify habitat requirements and major potential threats are high priority actions for this bird. Sunday 23 January – 16.00 to 16.20 The status and taxonomy of the world’s owls: an overview
The paper will begin by considering owls (Order Strigiformes, suborder Strigi) that are at risk by descending category of risk according to the IUCN categories: from Critical: Otus capnodes, Otus pauliani, Otus insularis and Athene blewitti; to Endangered: Tyto soumagnei, Mimizuku gurneyi, Bubo philippensis, Bubo blakistoni and Scotopelia ussheri; and Vulnerable: Tyto nigrobrunnea, Tyto manusi, Tyto aurantia, Phodilus prigogenei, Otus sagittatus, Otus ireneae, Otus angelinae, Otus longicornis, Otus mindorensis, Otus fuliginosus, Bubo vosseleri, Glaucidium albertinum, Ninox strenua, Ninox rudolfi, Strix davidi and Nesasio solomonensis. In each case, we will look at numbers, and at the factors threatening the species. Next we will consider some major issues in the taxonomy of owls, the Otus scops and Otus bakkamoena complexes in Eurasia, with particular reference to Otus lettia and lempiji; and the Otus guatemalae complex in Central and South America. Saturday 22 January – 9.50 to 10.40
The Flammulated Owl’s small size, strict nocturnality, and obligate insectivory render it particularly vulnerable to potential food shortages during unpredictable cold, wet spring weather patterns in the northern portions of its range. This may be especially critical to migratory northern populations upon their arrival at nesting areas with their immediate demands for food provisioning for energy recovery, territoriality, and egg-laying. We studied a small population of nesting Flammulated Owls in the Sublett Mountains of southcentral Idaho from 1991 to 1997. Four years of successful reproductive efforts by 3 to 8 nesting pairs of owls was followed by two consecutive years of non-breeding. In 1997 four breeding pairs were once again documented. An examination of climatological data from surrounding weather stations suggests probable weather influences on the nesting activity through precipitation and temperature impact on nocturnal insect activity, owl food supply, and energetics. Our evidence suggests that nesting successes are likely related to optimal timing of warmer temperature and lower precipitation during courtship, incubation and nestling periods of the owls’ nesting season, while opposing conditions may contribute to nesting failure. Thursday 20 January – 14.30 to 14.50 Dispersal strategies in Finnish owls: results from ringing.
Since 1974, Finnish ringers have been especially encouraged to work on birds of prey. More than 30 000 potential nest sites for owls are checked annually; and up to 1999, altogether more than 190 000 owls have been ringed in Finland. I calculated dispersal distances by using both recoveries of owls found dead in the breeding season, and recaptures at the nest. As predicted, natal dispersal distances were much shorter (medians 20–50 km, maxims 300 km) in the more generalist feeders, the Eagle Owl (Bubo bubo), Pygmy Owl (Glaucidium passerinum) , Tawny Owl (Strix aluco) and Ural Owl (Strix uralensis), than in the ‘real’ microtine specialists, the Northern Hawk Owl (Surnia ulula), Great Grey Owl (Strix nebulosa), Long-eared Owl (Asio otus), Short-eared Owl (Asio flammeus) and Tengmalm’s Owl (Aegolius funereus), which may breed several hundreds or even thousands of kilometres away from their natal area. In the Tengmalm’s Owl, the natal dispersal distance of the male was significantly shorter than that of the female, but in the Tawny and Ural Owls no corresponding sexual bias was found. The owlets born in peak microtine years, which were followed by a population crash of voles, seem to have bred, in general, farther from their natal sites than the owlets born in other phases of the 3–4 year cycle. According to Finnish data, both sexes of the Ural Owl and Tawny Owl and males of the Tengmalm’s Owl are highly tenacious to their breeding sites. Tengmalm’s Owl females, however, may breed several hundred kilometres away from their previous breeding site. Much more recaptures at the nest are needed before reliable conclusions on the breeding dispersal of the other species can be made. Thursday 20 January – 9.50 to 10.40 Home-range, movement and dispersal of Lanyu scops owls (Otus elegans)
Lanyu is a tropical island 45 km2 in size SE of Taiwan. The small and primarily insectivorous Lanyu scops owl (Otus elegans) inhabits wooded areas on the island. The amount of suitable habitat with nesting cavities is quite limited. The number of owls seen in good habitat shows large seasonal fluctuation, with very high density during the breeding season. Radio tracking of adult breeders reveals relatively long distance movements between seasons. Only some adults remain in the breeding area year round. Apparently breeders crowd into suitable habitat before each breeding season, and disperse to peripheral habitat after the breeding season. Female sub-adults disperse farther from natal area than males. There is no habitat segregation between adults and sub-adults. The home-range sizes of breeding birds are small with large overlaps while non-breeders roam large areas covering the home-ranges of several pairs. Wednesday 19 January – 11.30 to 11.50 Island habitat saturation and breeding competition of Lanyu scops owls (Otus elegans)
Lanyu scops owl (Otus elegans) is the dominant resident owl on the small tropical Lanyu island SE of Taiwan. A few brown hawk owl Ninox scutulata shares the habitat. Suitable breeding habitat appears to be saturated. Owl density in good breeding habitat exceeds 10 birds/ha. Lanyu scops owls compete intensely with each other for tree cavities during breeding season. Only 41.12% of the adults present can breed. In good habitat, as many as 7 males may compete for the use of one nest cavity. Even if a male or a female owl succeeds in obtaining a cavity early in the season, a high percentage of them lose its ownership before egg laying time. Cavity ownership turn-over is common. Analyses are made of factors such as age or body size which potentially could influence the outcome of a competition. Brown hawk owls do not exert great nesting pressure on Lanyu scops owls because of their low density. Thursday 20 January – 11.50 to 12.10 Large Forest Owls in southeast NSW: Recent surveys and management initiatives
M. Crowley, PO Box 42 Batemans Bay 0244726211 Over the past 12 years, large owls have been progressively the target of more intense management interest in the southeast forest of NSW. Before 1988, the basic distribution and abundance of large forest owls was unknown in this region of NSW. Several regional surveys have since been conducted in the area, largely by State Forests of NSW, and in particular by Rod Kavanagh. During the same time period, large changes in land use and tenure have occurred, as well as several "stochastic events" (fires, floods, drought). At present, large owls appear to be present in detectable populations across the forested landscape. This paper reports on recent (1995-99) repeat surveys of known sites and owls. Relationships with survey effort, forest management and owl biology are presented. Basic requirements for information needed to manage owls in the future, in particular knowledge of reproduction rate (fecundity) and mortality rate, are discussed. Sunday 23 January – 15.40 to 16.00
We studied the spatial distribution of California spotted owls (Strix occidentalis occidentalis) with respect to habitat type and availability within the San Bernardino Mountains of southern California. We located 130 unique owl territories within the range. We calculated a minimum crude density of 0.14 owls/km2, and an ecological density of 0.40 owls/km2. Owls varied in distribution and density among three major habitat types: canyon live oak (Quercus chrysolepis)/big-cone Douglas fir (Pseudotsuga macrocarpa) (62 territories); mixed conifer (41 territories); mixed conifer/hardwood(27 territories). Density of territories in each of the habitats were 0.43, 0.11 and 0.20 territories/km2, respectively. The mean nearest neighbor distance of territory centers was 1,564 m with a minimum distance of 664 m. The spatial distribution of observed owl sites was significantly different than expected from a random distribution of sites (c 2 = 30.71, df = 5, P < 0.001). Nesting and non-nesting owls used spatial habitat configurations that were different from available areas at 3 ha, 20 ha, 79 ha, 177 ha, 314 ha and 707 ha scales, respectively. However, owl nest sites differed from owl non-nest sites only at the level of 3 ha plots, suggesting nesting activity may be influenced by factors other than habitat configuration. Fragmentation of suitable habitat was significantly greater at non-nesting owl sites and random sites than it was at nesting owl sites . Sunday 23 January – 11.30 to 11.50
Early studies of the Powerful Owl (Ninox strenua) focused on populations in wet eucalyptus forest, and only recently have drier habitats received much attention. This 2-yr research project on owl ecology in the dry Box-Ironbark forest of central Victoria was designed to guide forest management policies for this threatened species. Four owls (two males and two females) were radiotagged prior to breeding with tail-mounted transmitters. Home range sizes of these birds were larger than previously speculated, with one female using 2400 ha in the first six nights of tracking, and subsequently covering over 3000 ha. These extensive foraging areas were due, in part, to low numbers of the preferred prey (arboreal marsupials), and owls relied heavily on alternative prey such as large birds. Most prey species in this habitat are dependent on tree hollows, and their sparse densities reflect the scarcity of old, hollow-bearing trees after a century of intensive human exploitation. The home range selection by 15 owl pairs was compared to the broader forest in terms of the abundance of large old trees and tree hollows. Owls selected areas that had significantly more large trees (67% greater) and hollows (177%) on average, suggesting that habitat quality was limiting the sparsely distributed owl population. The relatively low reproductive success of Powerful Owls in this habitat, combined with recently observed loss of known breeding pairs, indicates that local extinction is possible. This could be counteracted most effectively by improved habitat management that returns the forest to a more natural state. Sunday 23 January – 12.10 to 12.30 Current distribution and status of the Blakiston’s Fish Owl (Ketupa blakistoni) in Japan.
One of largest owls in the world, Blakiston’s Fish Owl (Ketupa blakistoni) is distributed in a small part of the Far East. Hokkaido Island is the only place the owls are found in Japan, and the species has been nominated for inclusion in Japan’s RDB because of reduced numbers. Although a literature review and specimen records show a distribution of the owls all over Hokkaido in the past, field research from 1991 onwards has found only 50 owl sites, and the current population is estimated to be about 120 - 150. The current distribution clearly shows fragmentation between the sites, and inbreeding was observed for several pairs. Many breeding pairs depended on artificial feeding (20%) and nest boxes (40%) for raising their young, exigencies that reflect habitat-quality degradation. The landscape and natural resources of Hokkaido have been completely modified over the past century, causing significant habitat degradation - in terms of forest area, availability of large trees for nesting, and fish biomass for food; hence, fish owls have been driven close to extinction. This decade, government has supported both the expansion of the captive population and activities such as artificial incubation and dispersal to bolster the wild population. However, few habitat recovery programs have been conducted. From the point of view of a field scientist, consideration of the reasons for population decline is paramount, and we must address the problem of habitat recovery for the successful conservation of the owls. Saturday 22 January – 11.50 to 12.10 Breeding site occupancy in relation to site quality in a population of barn owls Tyto alba
There is considerable evidence from a variety of species that birds preferentially occupy breeding areas of highest quality. To test if such trends were also found in Barn owls, data on site occupancy collected over 20 years for a population of the owls in farmland habitat in south Scotland were compared with independent assessments of site quality. The habitat was a mosaic of small woodlands set among enclosed fields most of which were pasture at altitudes from 50-150 m above sea level. The birds caught around 85% of their prey along the edges of the woodlands and during the breeding season hunted mostly within a 1 km radius of their nests. The amount of woodland edge within 1 km of the nest was used as an index of site quality. Annual survival of adults was independent of amount of woodland edge within 1 km but deaths occurred mainly in winter when the birds ranged up to 5 km from their nests. The number of young fledged per pair at each site was significantly correlated with amount of woodland edge within 1 km. However, there was no evidence that the most productive sites were occupied most frequently. Over the 20 year study percentage occupancy was independent of site quality expressed either as the density of suitable foraging habitat (woodland edge) or as mean productivity. Once established at a site, less than 5% of breeding birds moved to other sites in subsequent years, even though better quality sites were frequently available close by. Also new recruits to the population did not settle preferentially in the best available sites. Reasons for this apparent inability to identify or to settle in the highest quality areas and its implications for the dynamics and conservation of the population are discussed. Thursday 20 January – 9.00 to 9.50 Distribution and habitat of Barking Owls (Ninox connivens) in the west region of Victoria
The objectives of the study reported here were to determine the status and habitat associations of the endangered Barking Owl, Ninox connivens, in the West Region of Victoria. The study confirmed existing perceptions that Barking Owls are extremely rare in the area, being recorded at only 4.3% of 257 sites surveyed in potentially suitable habitat. The owls were found at only 8% of 75 sites where they had previously been reported and listed in the Atlas of Victorian Wildlife, suggesting that the accumulated Atlas records may not give an accurate representation of current distribution and abundance. There seem to be only three main concentrations of population; in the Greater Grampians and adjacent Dundas Tablelands, in the Goldfields and in the Northern Inland Slopes. Further intensive surveys of each these areas are needed to clarify the status of the species more fully. Differences in some aspects of habitat were found at sites where Barking Owls were recorded compared with sites where they were not. Sites with owls had significantly higher densities of large trees and also had higher densities of tree hollows of a range of sizes including those suitable as nesting places for Barking Owls. Sites with owls were also closely associated with hydrological features such as rivers and swamps. Wednesday 19 January – 11.10 to 11.30 Infertility as a cause for egg inhatchability in the Barn Owl (Tyto alba) in the Netherlands.
Egg hatching failures are not uncommon in the avian world. For example, in the European Sparrowhawk (Accipiter nisus) 5% of the eggs fail to hatch, while in the Barn Owl this figure varies between 15 and 31%. Both the direct and indirect factors that cause egg inhatchability are generally unknown. To investigate why some eggs fail to hatch, unhatched eggs of Barn Owls (1998-'99, n=200) were collected and opened. Most eggs (67%) contained embryos, showing a variety of structural anomalies. The aim of the present work was twofold: to establish whether eggs without embryos were unfertilised, and to determine whether the anomalies could be due to parthenogenetic development. To determine egg fertility, yolk membranes were sampled and used for fluorescent detection of excess sperm cells. In 70% of the eggs without embryonic development, sperm cells were present and considered fertile. On the other hand, some eggs showing embryonic development had no sperm cells in their yolk membranes. This might be an indication of parthenogenetic development, but could also be due to degeneration of the yolk membrane. DNA analysis of yolk membranes and embryos is currently under way to enable the distinction between parthenogenetic development and membrane degeneration. In a similar parallel study in the Sparrowhawk, parthenogenetic development was found to be extremely rare (a single case in 250 eggs was supported by DNA evidence). In conclusion, lack of fertilisation is a minor cause for egg inhatchability in the Barn Owl (10% of the eggs), and absence of embryonic development is a poor indication of egg infertility. Thursday 20 January – 11.10 to 11.30 Tracking Tunnels vs Tracking in an East Australian Woodland.
Many nocturnal raptors prey on small mammals. To better understand the ecology of these raptors it is necessary to obtain an estimate of prey abundance. We used two techniques - live trapping with Elliot traps, and tracking tunnels (square ducting with ink pad and papers) - to assess the abundance of two native marsupials (Antechinus flavipes and Sminthopsis murina) and two introduced small mammals, the black rat (Rattus rattus) and the house mouse (Mus domesticus), at our field site in central western NSW. To our knowledge this is the first time the tracking tunnel technique has been used to assess the abundance of small native mammals in Australia, although it is used commonly in New Zealand. We present here a comparison of the two techniques. A. flavipes and S. murina appear to be detected more readily by the tracking tunnel technique, but at this stage the data set is sparse. House mice appear to be detected equally well by both techniques. Black rats appear to be detected readily in tracking tunnels, but were captured infrequently. The results suggest that tracking tunnels may be a useful, non-invasive, and in some cases superior technique for assessing the abundance of small mammals. We outline studies to investigate further the use of the tracking tunnel technique. Abundance of Nocturnal Birds in Central–Western New South Wales
From July 1994 to the present regular spotlight counts have provided an index of abundance of Rabbits Oryctolagus cuniculus, Common Brushtail Possums Trichosurus vulpecula, Common Ringtail Possum Pseudocheirus peregrinus and kangaroos Macropus spp. at Lake Burrendong ((320 42' S, 1490 10' E). Since February 1997, after the arrival of Rabbit Calicivirus Disease, the counts also included nocturnal birds. In addition from November 1996 to October 1997 monthly surveys were conducted using play-back calls of the Powerful Owl Ninox strenua, Barking Owl N. connivens, Barn Owl Tyto alba and Masked Owl T. novaehollandiae. The Atlas of Australian Birds (1984) indicates that the Powerful Owl, Barking Owl, Southern Boobook N. novaeseelandiae, Barn Owl, Tawny Frogmouth Podargus strigoides, White-throated Nightjar Eurostopodus mystacalis, Spotted Nightjay E. argus and Australian Owlet-nightjar Aegotheles cristatus could possibly be found in the area. Calls of the Masked Owl were included in the survey because of lack of information on the distribution of this species. Despite intensive surveys and suitable habitat, the Powerful Owl, Masked Owl and Barking Owl were not recorded. The Barn Owl, Southern Boobook and the Nightjars were recorded very occasionally whilst only the Australian Owlet-nightjar and the Tawny Frogmouth, both of which breed in the area, were regularly recorded. Data on the abundance of potential nest sites, and prey items such as small mammals and birds will be presented. Although wide spread, the most likely limiting resource appears to be an unreliable supply of the House Mouse Mus domesticus and other small mammals within the lightly grazed, conservation landscape. Studies of Ural owls (Strix uralensis) in Honshu, Japan
Little is known about the ecology of Ural owls (Strix uralensis) in Japan. It is a widespread but scarce species, and may well be threatened by unsympathetic forest management. Around 70% of the land surface of Japan is forested, but 41% of this area is managed for timber production. With so little known about the basic requirements of Ural owls, research is urgently needed into how forests can be better managed for this important species, and other forest wildlife. Wildlife conservation is a relatively new concept in Japan. We are looking at Ural owls in three study areas in Honshu, the largest of the Japanese islands. Two studies are based on the use of nest boxes in managed forests. One is in pine forest that has been planted along the northern coast, while the other is in more varied forest around Mount Fuji. We are investigating how the composition and structure of forests influence breeding performance, diet, and ranging behaviour. In our third study area, near the city of Kofu, we are looking at the use of natural nest sites. We have found a close association between Ural owls and human communities in rural areas. Most nest sites are in villages, because it is here that some of the largest trees are to be found. Old trees in the grounds of temples and shrines are particularly important. This may be because the surrounding forest lacks old trees with suitable cavities for nesting, and this is one aspect that we are investigating. Survey Techniques for the World's Owls - Fundamentals to Conservation
Surveying for owls is fundamental to their conservation. Many techniques to determine the presence (or absence) of owls have been developed. Likewise, a number of techniques are being used to find owl nests and study the demographic performance of owls. Survey techniques differ with the species of owl being surveyed, their habitats, their nocturnal/diurnal habits, the tools and technology available to the surveyors, and the safety concerns of the surveyors. The purpose of this study is to develop an information system around the techniques for locating and studying basic demographic aspects of the owls of the world. Summaries from this work will provide methodologies and technologies that have proven successful (as well as unsuccessful) in studying owls across the globe. This project is just beginning; the Owls 2000 conference as a good means to begin collecting materials for this project. Of particular interest, the authors are desiring copies of survey protocols, published or unpublished survey techniques, and reports/notes on successful (and unsuccessful) survey efforts. The authors will be providing a "Survey Techniques Form" at the conference to solicit specific information. As part of this project, the authors will also be developing a network of owl researchers from around the world with experience, or an interest, in survey techniques. Diet of the Powerful Owl, Sooty Owl and Masked Owl in south-eastern Australia
The places where owls obtain their food and what they eat have a critical bearing on our understanding of the habitat requirements of these birds. A total of 1674 prey items from 48 Powerful Owl (Ninox strenua) territories, 1466 prey items from 28 Sooty Owl (Tyto tenebricosa) territories, and 160 prey items from 7 Masked Owl (T. novaehollandiae) territories were analysed. There was virtually no overlap between the diets of the Powerful Owl, assessed across all sites, and the Masked Owl. The Powerful Owl preyed almost exclusively on arboreal mammals, most of which were in the weight range of 50-100% of adult owl body weight, supplemented by diurnal birds. In contrast, the Masked Owl preyed almost exclusively on small terrestrial and scansorial mammals, most of which were in the weight range of 3-20% of adult owl body weight, supplemented by diurnal birds. At any one site, both owls appeared to specialise on just one or two prey species. The diet of the Sooty Owl was strikingly different by its generalist nature. The Sooty Owl preyed on a wide range of both arboreal and terrestrial or scansorial mammals at any one site, most of which were in the weight range of 2-100% of adult owl body weight. The Sooty Owl appeared to take any available small and medium-sized mammal and foraged throughout its more limited habitat from the forest canopy to the ground. Geographical variation in owl diets were related to differences in the availability of potential prey. All three species survive and breed successfully in the coastal and foothills forests of south-eastern NSW on a diet composed principally of prey species that are not dependent on old-growth forest.
Fragmentation of native forest and woodland by clearing for agriculture and urban developments has had a greater effect on large forest owls and their arboreal marsupial prey than logging. In this study, assessments were made of the contribution of forest and woodland fragments on privately-owned and unprotected lands towards the regional conservation of these species in south-eastern New South Wales. Small (<200 ha) fragments did not provide a significant reservoir for populations of the Powerful Owl (Ninox strenua), Sooty Owl (Tyto tenebricosa) and Masked Owl (T. novaehollandiae). Virtually all records of these owls in the region were associated with extensively forested areas or occurred within 1 km of the boundary of these areas (mainly state forests, national parks and nature reserves). Several important prey species, in particular the Common Ringtail Possum (Pseudocheirus peregrinus), Greater Glider (Petauroides volans), Yellow-bellied Glider (Petaurus australis) and the Sugar Glider (Petaurus breviceps), were either absent or less abundant in small forest fragments. The Barn Owl (Tyto alba), a non-forest species, and two other nocturnal "forest" birds, the Southern Boobook (Ninox novaeseelandiae) and Australian Owlet-nightjar (Aegotheles cristatus), were surprisingly common in small forest and woodland fragments. Owls in the South-West Forests of Western Australia
The first systematic survey of owls in the south-west forests of Western Australia was conducted during early spring (Sept. 13-25) 1999. This study focused on the Masked Owl (Tyto novaehollandiae) and the Barking Owl (Ninox connivens) and covered an area from Toodyay (near Perth) in the north to Augusta in the south and York/Narrogin in the east and Stirling Range National Park and Two Peoples Bay (near Albany) in the south-east. Seventy sites, stratified by major forest type (Jarrah, Karri, Wandoo) and logging history (up to three categories), were surveyed once each, and all nocturnal birds and mammals seen or heard were recorded. A further 30 sites were surveyed to sample transitional vegetation communities (e.g. Jarrah/Wandoo woodland), forest fragments (e.g. Tuart woodland), and forests at a number of outlying locations (e.g. Boranup, Dryandra, Boyagin and the Stirling Ranges). The survey method employed a standard period of listening for unelicited calls, followed by broadcasting of pre-recorded calls of the Masked Owl and the Barking Owl and listening for a response, followed by a period of spotlighting to estimate the numbers of animals at each site. A total of 119 Tyto and Ninox owls were recorded at 67% of sites: 114 of which were Southern Boobooks (Ninox novaeseelandiae) and 5 were Masked Owls. Thirty Australian Owlet-nightjars and 11 Tawny Frogmouths were also recorded at the sites. Eighty-three owls were recorded within the main forest belt and 36 were recorded from the outlying forest sites. No Barking Owls were recorded during this survey of public forest lands, although there were some reports of this species occurring on privately-owned land outside or adjacent to the main forest belt. This was a preliminary survey to obtain baseline information about the distribution of owls in the south-west forests. The survey will be repeated in autumn 2000. Members of the public are encouraged to contribute their observations of owls, particularly those occurring on private lands, so that a better picture can be developed about the distribution and abundance of these owls in the South-West. Are ecotones important for the Masked Owl?
The Masked Owl (Tyto novaehollandiae) is widely distributed throughout the forests of north-eastern New South Wales and it is frequently recorded during nocturnal call playback surveys. However, little is known of its habitat requirements, diet and breeding biology because only a handful of nest sites and roost sites have been located. Correlative studies by others, based on call playback surveys, suggest that the Masked Owl is associated with dry, open eucalypt forests having a sparse understorey and many old, hollow trees. Masked Owls are also recorded occasionally as road-kills near the edges of forest and farmland. This study reports the discovery of a Masked Owl roost site in Girard State Forest near Tenterfield and the analysis of 35 prey items contained within about 30 regurgitated pellets found at the roost site. The diet of this owl was predominantly European Rabbit (Oryctolagus cuniculus) and two species of Bandicoot (Perameles nasuta and Isoodon macrourus), suggesting that it may forage near the structural ecotones within forest or near the ecotone between forest and semi-cleared farmland. Surveys at 147 call-playback locations in the district between 1997-1999 recorded Masked Owls at 23 sites, most (70%) of which were within 1 km of the forest boundary. Further work involving radio-tracking is required to determine whether the owls do indeed forage preferentially near the ecotone between forest and farmland and/or near the ecotones between forests of different structural composition.
The Malagasy Scops-Owl Otus rutilus is comprised of two main populations on Madagascar that differ in a suite of morphological and vocal characters. These populations, which occupy different habitats and geographic areas, are best treated as distinct biological species. Although a previously unrecognized 1866 type specimen exists for the western species, a valid name does not, so we are establishing for it a new specific epithet, while the eastern species retains the name Otus rutilus. The western species occurs in a wide variety of dry forest and degraded habitats, while rutilus is probably restricted to rainforest, from lowlands through the montane zone. The western species is characterized by having a more distinct facial disk rim, shorter and less profuse facial bristles, more heavily streaked upperparts, more prominently banded central rectrices, a longer, more graduated tail, more finely marked underparts, more extensively feathered tarsi, and darker claws than rutilus. It usually occurs in grey to dull brown morphs, while rutilus usually occurs in rufous and dark warm brown morphs. All characters are variable but in combination nearly every specimen is identifiable to species, both qualitatively and quantitatively. Juvenile rutilus resemble the western species in pattern of underparts, back streaking, and tail banding. The song of the western species is harsher and sounds lower; each phrase contains several very short notes (rather than a single, longer note per phrase), and each phrase has distinct harmonics. Additionally, morphology and vocalisations confirm that all small-island taxa previously treated as conspecific with Otus rutilus require treatment as biological species. Population status of owls in Kharkov region, north-eastern Ukraine.
Kharkov region, due to its geographic position, comprises a variety of steppe and forest landscapes. There is a long history of bird studies here, which allow observations on population trends over a one hundred year period. Twelve species of owls, with six species breeding, have been recorded in this region. A population census conducted from 1991 to 1995 showed a decline in the density of all owl species. The last breeding records of the Eagle Owl (Bubo bubo), previously a common species, were from the mid-1970s. Short-eared Owl (Asio flammeus) and Scops Owl (Otus scops) are seriously threatened. Few breeding pairs remain from previously abundant populations of these species. The Tawny Owl (Strix aluco) is still common, with up to 10 pairs occurring per 10 km2 in old forests. Populations of the Short-eared Owl and the Tawny Owl suffer the loss of breeding habitats. The other major threat is shooting and disturbance. Population trends and threatening factors are discussed. Daily variation of the meal to pellet interval in the Long-eared Owl (Asio otus).
Pellet analysis, despite its known limitations, is a commonly used method in studies of owl ecology. Pellets provide a unique opportunity to examine the prey spectrum but give little information on daily food intake. Previous studies proved that the production of pellets in captivity is affected by a number of factors such as the meal size, composition of food, feeding schedule, availability of food, length of nocturnal period, age and individual traits of birds. In the wild, these parameters seem to make the timing of pellet production virtually unpredictable. However, it is known that despite variability of the meal to pellet interval a number of species tend to regurgitate pellets at certain times of day ie in the night and just before sunset. The present study tested the hypothesis that the meal to pellet interval changes depending on meal time so that the probability of pellet egestion is higher at particular times of day. Experiments in captivity on the Long-eared Owl showed an extensive circadian variation of the meal to pellet interval. The pattern of this variation can be used in field studies for the analysis of daily food rations. Possible adaptive values of this daily pattern and its use in the pellet analysis are discussed.
Blakiston’s Fish Owl (Ketupa blakistoni), one of the endangered species of Japan, is one of the most important gods for the Ainu people, the native people of Hokkaido, Japan. Fish owls were called "kotan kor kamuy," which means the god of the village. Traditionally the Ainu were a hunting-gathering culture, totally dependent on natural resources, and over time developed an Animistic theology in which all animals were believed to be divine; most admired were bear and the fish owl. Because fish owls mainly eat fish, salmon in the autumn is the most important food for owls, allowing them to prepare for winter food shortages; thus, unfrozen spawning grounds are the owls’ most important habitat. Furthermore, as the owl nests in large cavities of broad-leaved trees, deciduous forests of elm, walnut, and oak are also important. Such unfrozen spawning grounds, nut-bearing trees, and large trees, were also very important places for the Ainu. Thus, the territories of fish owls and Ainu villages naturally overlapped, and it is easy to imagine that the Ainu highly revered fish owls. Unfortunately, since the Ainu never developed a written language, most folklore about fish owls were conveyed orally; however, early explorers and researchers did record the importance of fish owls. Indeed, the Fish Owl Ceremony, which returned the spirit of fish owls to the god’s world, was conducted until the 1930s. Thus, understanding the relationship between fish owls and native Ainu people is important not only to ethnology, but is also significant for nature conservation.
|
