Australian National University
Canberra, Australia
19-23 January 2000
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Manning
Clarke Centre Australian National University Canberra, Australia 19-23 January 2000
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The Owls 2000 conference 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.
| Welcome
Letter to Delegates On behalf of the Australasian Raptor Association it is with much pleasure that I welcome you to Owls 2000. This is the first international conference hosted by our association and we are pleased that you have supported this event. The program over the next five days includes a range of activities and social opportunities which I'm sure you will find a rewarding experience. With such an exciting array of papers, delegates from all parts of the globe and from diverse backgrounds; and a terrific venue, we're poised for not only a really enjoyable conference but one which promises to make a significant contribution to research on owls and their conservation. I trust that the information presented during the sessions and the Discussions which will follow stimulates robust and positive debate. Through this I hope that we can all take home some new ideas on how we can ensure that owls and their habitat survive for generations (millennia) to come. Mark Holdsworth President
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Organising Committee Mr Mark Holdsworth Australasian Raptor Association - Hobart Dr Iain Taylor Dr Rod Kavanagh Dr Jerry Olsen Mr Bob Digan Mr Malcolm Fyfe Mr Nick Mooney Conference
Secretariat Email: owls2000@con-sol.com |
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:
Abstracts and posters are listed in alphabetical order.
At the time of printing no abstract from PP Singh was received.
Speakers, topics and times are correct at the time of publishing and, in the event of unforseen circumstances, the organisers reserve the right to alter or delete items from the Symposium Program.
Posters
Arthur, T., Gifford, E., Pech, R. and Davey, C. Tracking tunnels vs tracking in an East Australian woodland.
Davey, C. and Pech, R. Abundance of nocturnal birds in central–western New South Wales
Higuchi, A. Aoki, S. and Abe, M. Studies of the Ural Owl in Honshu, Japan.
Johnson, D.H. and Marcot, B.G. Survey Techniques for the World's Owls - Fundamentals to Conservation.
Kavanagh, R.P. Diet of the Powerful Owl, Sooty Owl and Masked Owl in south-eastern Australia.
Kavanagh, R.P. and Stanton, M.A. Response to habitat fragmentation by the Powerful Owl, Sooty Owl and Masked Owl in south-eastern Australia.
Liddelow, G.L., Wheeler, I.B. and Kavanagh, R.P. Owls of the South-West Forests of Western Australia.
McCray, K. and Kavanagh, R.P. Are ecotones important for the Masked Owl?
Rasmussen, P.C., Schulenberg, T.S., Hawkins, A.F.A. and Voninavoko, R. Geographic variation in the Malagasy Scops Owl (Otus rutilus), and the existence of an unrecognised species.
Singh, P.P. and C.S. Malhi. Feeding and nesting ecology of the Spotted Owlet, Athene brama
Sova, M. Population status of owls in the Kharkov region, north-eastern Ukraine.
Sova, M. Daily variation of the meal to pellet interval in the Long-eared Owl (Asio otus).
Takenaka, T. Relations between the Blakiston’s Fish Owl (Ketupa blakistoni) and the Ainu people in Japan: a review and introduction.
Comparative habitat use by Owls in a high altitude (1700 – 3000 m) Rocky Mountain forest
Anderson, Stanley H., Wyoming Cooperative Fish and Wildlife Research Unit,
University of Wyoming, Box 3166, Laramie, WY 82071.
Clark, Kathleen A., Wyoming Cooperative Fish and Wildlife Research Unit,
University of Wyoming, Box 3166, Laramie, WY 82071.
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
Arrowood, Patricia C. Department of Fishery and Wildlife Sciences, New Mexico State University, Box 30003, Dept. 4901, Las Cruces, NM 88003, USA E-mail: parrowoo@nmsu.edu
Carol A. Finley, Courtney Blood, and Bruce Thompson. New Mexico Cooperative Fish and Wildlife Research Unit and Department of Fishery and Wildlife Sciences, New Mexico State University, Box 30003, Dept. 4901, Las Cruces, NM 88003, USA.
Eugene S. Botelho. 58 Ohio St., New Bedford, MA 02745, USA
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
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Thursday 20 January – 12.10 to 12.30
Bell, P. J. Nature Conservation Branch, Department of Primary Industry Water and Environment, P O Box 44A, Hobart 70001 <phillb@dpiwe.tas.gov.au.>
Mooney, N. Nature Conservation Branch, Department of Primary Industry Water and Environment, P O Box 44A, Hobart 70001 <nickm@dpiwe.tas.gov.au.
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:
Brett Cann, State Forests NSW, Taree
Justin Williams, State Forests NSW, Wauchope
Jim Shields, State Forests NSW, Coffs Harbour
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.
Clancy, G.P. PO Box 63 Coutts Crossing NSW 2460 Australia
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
Cooke, R. School of Ecology and Environment, Deakin University – Rusden Campus, Clayton, Victoria 3168
Wallis, R. School of Ecology and Environment, Deakin University – Warrnambool Campus, Warrnambool, Victoria 3280
Webster, A. Department of Natural Resources and Environment, Port Phillip Region, Box Hill, Victoria 3128
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
Debus, S.J.S. Division of Zoology, University of New England, Armidale,
NSW 2351, Australia
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
Einoder, L.D. University of Tasmania, Hobart.
35 Grosvenor St, Hobart, TAS, Australia, 7005.
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
Enríquez, Paula L. Depto. de Ecología y Sistemática Terrestre, El Colegio de la Frontera Sur, Apartado Postal 63-29290, San Cristóbal de las Casas, Chiapas, México.
Johnson D.H., Northwest Habitat Institute, 2344 Summit Lake Shore Road NW, Olympia, WA 98502, USA
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
Eric D. Forsman, U. S. Forest Service, Pacific Northwest Experiment Station, 3200 SW Jefferson Way, Corvallis, Oregon, USA 97330
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
Eric D. Forsman, U. S. Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson Way, Corvallis Oregon 97330 USA
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
Garvey, J.M. Department of Zoology, La Trobe University, Bundoora, Victoria, 3083.
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
Stephen Henry, Andrew McIntyre*, Michael Bramwell and Peter Kambouris
Department of Natural Resources and Environment, PO Box 260, Orbost, Victoria, Australia, 3888. (e-mail Stephen.Henry@nre.vic.gov.au)
*Present address: New South Wales National Parks and Wildlife Service, Coffs Harbour, NSW
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
David Hollands
Orbost, Victoria 3888. Email: margholl@bigpond.com.au
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
Hinam, Heather, L. Department of Zoology, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
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
Farah Ishtiaq, Bombay Natural History Society, Hornbill House, S. B. Singh Road, Mumbai-4000 23, India
Asad R. Rahmani, Bombay Natural History Society, Hornbill House, S. B. Singh Road, Mumbai-4000 23, India
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.
References
Ali, S. and S. D. Ripley 1987 Handbook of the birds of India and Pakistan. Compact Edition. Oxford University Press.
King, B. and P.C. Rasmussen 1998. Rediscovery of the Forest Owlet Athene blewitti. Forktail 14: 51-53.
Rasmussen, P.C. and N. J. Collar 1998. A major specimen fraud in the Forest Owlet Athene blewitti. Ibis 141: 1-12
Wednesday 19 January – 14.10 to 14.30
Conservation and management of large forest owls in south-eastern Australia
Kavanagh, R.P. Forest Research Division, State Forests of New South Wales, P.O. Box 100, Beecroft, NSW, Australia, 2119. Email: rodk@sf.nsw.gov.au
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
Kavanagh, R.P. and Stanton, M.A. Forest Research Division, State Forests of New South Wales, P.O. Box 100, Beecroft, NSW, Australia, 2119.
Email: rodk@sf.nsw.gov.au
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
Indre Kirsten and Iain Taylor
The Johnstone Centre, School of Environmental and Information Sciences, Charles Sturt University, PO Box 789, Albury, NSW, Australia, 2640
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
Korpimäki, E., Hakkarainen, H., Ilmonen, P. and Wiehn, J.
Department of Biology, University of Turku, FIN-20014 Turku,
Finland (e-mail: ekorpi@utu.fi)
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.
Loyn, Richard H. Arthur Rylah Institute, Dept. Natural Resources & Environment (NRE), 123 Brown St Heidelberg, Victoria, Australia, 3084
McNabb, Edward G. Arthur Rylah Institute, NRE, 123 Brown St Heidelberg, Victoria, Australia, 3084
Volodina, Lioudmila. Royal Melbourne Institute of Technology, Melbourne.
Willig, Rolf. Forest Management, NRE, 8 Nicholson St, Melbourne.
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
Warwick Madden Research & Development Officer, Bayer Australia Limited, PO Box 903, Pymble NSW 2073 Email: warwick.madden.wm@bayer-ag.de
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
Bruce G. Marcot1, Peter Mark Cocker and David H. Johnson2
1 15381 SW Thurston Lane, Tigard, OR 97224 USA 503-808-2010 (w). email: brucem@spiritone.com 2 Northwest Habitat Institute, 2344 Summit Lake Shore Rd NW, Olympia, Washington, 98502 USA. 360-902-2603 (w); 360-902-2946 (fax); email: djnwhi@aol.com
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
E.McNabb, Edward G. Arthur Rylah Institute, Dept. Natural Resources & Environment, 123 Brown St Heidelberg, Victoria, Australia, 3084
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
D.R. Milledge, Landmark Ecological Services, PO Box 100, Suffolk Park, NSW 2481
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
Professor Ian Newton OBE FRS, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, United Kingdom
E-mail: i.newton@ite.ac.uk
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
Professor Ian Newton OBE FRS, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire PE17 2LS, United Kingdom
E-mail: i.newton@ite.ac.uk
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
Norberg, R. Ake. Department of Zoology, Zoomorphology, University of Goteborg, P.O. Box 463, SE-405 30 Goteborg, Sweden
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
Olsen, J. Applied Ecology Research Group, Division of Communication and Education, University of Canberra, ACT, Australia 2601
S. Trost, Erindale College, McBryde Cres., Wanniassa, ACT, Australia 2903
G. Hayes, Environment Australia, GPO Box 787, Canberra, ACT 2600
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?
Olsen, J. Applied Ecology Research Group, Division of Communication and Education, University of Canberra, ACT, Australia 2616
B.G. Marcot, 1221 S.W. Yamhill St., Suite 200, POB 3890, Portland OR USA 97208-3890
S. Trost, Erindale College, McBryde Cres., Wanniassa, ACT, Australia 2903
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
Olsen. P, Division of Botany & Zoology, Australian National University, Canberra, ACT 0200
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
Peake, P. 4/10 Abinger Place, Richmond, Victoria, 3121, Australia.
Robinson, D. Birds Australia, 415 Riversdale Road, Hawthorn East, Victoria, 3123, Australia.
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
John Penhallurick, Division of Communication and Education, University of Canberra, Canberra City. A.C.T. 2601, Australia
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
Powers, Leon R. Tegethoff, Jay B. and Cody D. Schneider, Department of Biology, Northwest Nazarene University, Idaho 83686
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.
Saurola, P.L. Ringing Centre, Finnish Museum of Natural History, P.O.Box 17, Fin-00014 University of Helsinki, Finland.
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)
Severinghaus, L. L. Institute of Zoology, Academia Sinica, Taipei, Taiwan, 11529.
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)
Severinghaus, L. L. Institute of Zoology, Academia Sinica, Taipei, Taiwan, 11529.
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
J. M. Shields, PO Box 219 Narooma, NSW 0244762489: Email - jims@sf.nsw.gov.au
C. Slade. PO Box 273 Eden, NSW 0264 961500
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
Smith1,R.B. P.O. Box 266, Mattituck, New York 11952
R.J.Gutiérrez2, Department of Wildlife, Humboldt State University, Arcata, CA 95521
W.S.LaHaye, P.O. Box 523, Big Bear City, CA 92314
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
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Sunday 23 January – 11.30 to 11.50
Soderquist, Todd. Arthur Rylah Institute, Victorian Department of Natural Resources and Environment, 123 Brown St, Heidelberg, Victoria, Australia 3084
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.
Takenaka, T. Environmental Earth Science, Hokkaido University, N10W5, Sapporo city, 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 r
