Sooty Owl Research Articles

Interpreting the mammal deposits of Cloggs Cave (SEAustralia),GunaiKurnaiAboriginal Country, through community‐led partnership research

AbstractPalaeontological animal bone deposits are rarely investigated through research partnerships where the local First Nations communities have a defining hand in both the research questions asked and the research processes. Here we report research undertaken through such a partnership approach at the iconic archaeological site of Cloggs Cave (GunaiKurnai Country, East Gippsland), in the southern foothills of SE Australia's Great Dividing Range.A new excavation was combined with detailed chronometric dating, high‐resolution 3D mapping and geomorphological studies. This allowed interpretation of a sequence of stratigraphic layers spanning from a lowermost excavated mixed layer dated to between 25,640 and 48,470 cal BP, to a dense set of uppermost, ash layers dated to between 1460 and 3360 cal BP. This long and well‐dated chronostratigraphic sequence enabled temporal trends in the abundant small mammal remains to be examined.The fossil assemblage consists of at least 31 taxa of mammals which change in proportions through time. Despite clear evidence that the Old Ancestors repeatedly carried vegetation into the cave to fuel cool fires (no visible vegetation grows in Cloggs Cave), we observed little to no evidence of cooking fires or calcined bone, suggesting that people had little involvement with the accumulation of the faunal remains. Small mammal bones were most likely deposited in the cave by large disc‐faced owls,Tyto novaehollandae(Masked Owl) orTyto tenebricosa(Sooty Owl).Despite being well dated and largely undisturbed, the Cloggs Cave assemblage does not appear to track known Late Quaternary environmental change. Instead, the complex geomorphology of the area fostered a vegetation mosaic that supported mammals with divergent habitat preferences. The faunal deposit suggests a local ancestral landscape characterised by a resilient mosaic of habitats that persisted over thousands of years, signalling that the Old Ancestors burned landscape fires to encourage and manage patches of different vegetation types and ages within and through periods of climate change.Read the freePlain Language Summaryfor this article on the Journal blog.

Effectiveness of joint species distribution models in the presence of imperfect detection

Abstract Joint species distribution models (JSDMs) are a recent development in biogeography and enable the spatial modelling of multiple species and their interactions and dependencies. However, most models do not consider imperfect detection, which can significantly bias estimates. This is one of the first papers to account for imperfect detection when fitting data with JSDMs and to explore the complications that may arise. A multivariate probit JSDM that explicitly accounts for imperfect detection is proposed, and implemented using a Bayesian hierarchical approach. We investigate the performance of the JSDM in the presence of imperfect detection for a range of factors, including varied levels of detection and species occupancy, and varied numbers of survey sites and replications. To understand how effective this JSDM is in practice, we also compare results to those from a JSDM that does not explicitly model detection but instead makes use of ‘collapsed data’. A case study of owls and gliders in Victoria, Australia, is also illustrated. Using simulations, we found that the JSDMs explicitly accounting for detection can accurately estimate intrinsic correlation between species with enough survey sites and replications. Reducing the number of survey sites decreases the precision of estimates, while reducing the number of survey replications can lead to biased estimates. For low probabilities of detection, the model may require a large number of survey replications to remove bias from estimates. However, JSDMs not explicitly accounting for detection may have a limited ability to disentangle detection from occupancy, which substantially reduces their ability to accurately infer the species distribution spatially. Our case study showed positive correlation between Sooty Owls and Greater Gliders, despite a low number of survey replications. To avoid biased estimates of inter‐species correlations and species distributions, imperfect detection needs to be considered. However, for low probability of detection, the JSDMs explicitly accounting for detection is data hungry. Estimates from such models may still be subject to bias. To overcome the bias, researchers need to carefully design surveys and choose appropriate modelling approaches. The survey design should ensure sufficient survey replications for unbiased inferences on species inter‐dependencies and occupancy.

The diet of a Sooty Owl from Yarrangobilly Caves, NSW

ABSTRACT A total of 783 dietary items from a Sooty Owl Tyto tenebricosa tenebricosa with suspected partial xanthochromism (yellow plumage colouration) was identified from Yarrangobilly Caves, NSW. Observations of the owl at the cave and collection of feathers suggest that prey items accumulated between 2011 and 2018. A total of 12 mammal species was detected in the diet, with the Bush Rat Rattus fuscipes, Agile Antechinus Antechinus agilis, Sugar Glider Petaurus breviceps and Rabbit Oryctolagus cuniculus dominating. The diet also included three threatened species, the Eastern Pygmy Possum Cercartetus nanus, Smoky Mouse Pseudomys fumeus and Broad-toothed Rat Mastacomys fuscus. The diversity of prey identified in the diet contrasts markedly with that found in studies of subfossil deposits from the area, supporting evidence of extensive mammal declines since European settlement.

A comparison of urban and peri-urban/hinterland nocturnal birds at Brisbane, Australia

This study identified and compared the abundance and detectability of owls and other nocturnal birds, over 1 year, in an urban parkland of a Brisbane suburb to a peri-urban/hinterland/rainforest site 27km away. Five owl species were detected, but only at the peri-urban/hinterland/rainforest site, they were powerful owl Ninox strenua, southern boobook Ninox boobook, sooty owl, Tyto tenebricosa, masked owl Tyto novaehollandiae and barn owl Tyto alba. A single southern boobook was detected outside the study, at the urban site. The tawny frogmouth Podargus strigoides was only detected at the urban site whereas the plumed frogmouth Podargus ocellatus plumiferus was only detected at the rainforest site. The bush stone-curlew Burhinus grallarius was the most frequently detected nocturnal species, yet we discuss its recent decline in Brisbane. Incidentally recorded mammals, reptiles, frogs and diurnal birds are given. The rainforest site had more scansorial mammals whereas the urban site had more possums, dogs and cats.

High predation risk for a small mammal: the eastern pygmy-possum (Cercartetus nanus)

We report high rates of predation within a population of eastern pygmy-possum (Cercartetus nanus) near Sydney, observed during a study of the impacts of logging on the species. Predation by reptiles was observed on six of 61 radio-tracked pygmy-possums, while two were suspected of being taken by raptors. We further investigated predation by sooty owls (Tyto tenebricosa) by identifying remains in pellets. Pygmy-possums comprised 15% of the 126 dietary items identified. Predation occurred at both logged and unlogged sites in our study. We suggest that documented high rates of predation in our study could make the species vulnerable to altered predation regimes, such as influxes of feral predators, and highlight the need for a better understanding of any influence of logging on predator activity.

Utility of owl pellets for monitoring threatened mammal communities: an Australian case study

Context Predictive modelling of the impacts of climate change has highlighted a need for on-ground monitoring of mammal communities within the Wet Tropics bioregion of Queensland to inform wildlife conservation management. Standard mammal-survey techniques are labour intensive and often incapable of detecting rare, trap-shy or otherwise elusive species, effectively rendering them invisible to researchers even when substantial resources are applied. Aims To assess the utility of feeding remains (regurgitated pellets) from lesser sooty owls, Tyto tenebricosa multipunctata, for monitoring populations of small to medium-sized mammals within the Wet Tropics. Methods Three female lesser sooty owls were radio-tracked to determine home-range areas. Radio-tracking and targeted systematic searches were used to locate diurnal roosts containing owl pellets from which prey species were identified. Owl-pellet data were directly compared with live-trap data within three putative owl home ranges. Additionally, analyses of a dataset spanning more than 15 years demonstrated the utility of owl-pellet data for monitoring mammal communities. Key results Owl-pellet surveys yielded 14 mammal species (840 individuals) from 152 man-hours, compared with six mammal species (361 individuals) from 194 man-hours of live trapping. Both survey methods identified Rattus fuscipes, Melomys spp. and Antechinus spp. as the most abundant species but live-trap data were found to under-represent relative abundance of Melomys spp. and over-represent relative abundance of R. fuscipes in comparison to owl-pellet data. Conclusions Analysis of lesser sooty owl pellets is a particularly useful method for compilation of species inventories of small to medium-sized mammals, being more effective than standard live-trapping surveys within the rainforests of the Wet Tropics. Implications Owl-pellet analysis is well suited for monitoring mammal communities, as long as periodic data are collected from the same roost(s) and the pellets have been deposited by the same individual bird(s). Additional research relating to variability in behavioural traits between individual lesser sooty owls that have potential to confound results via sampling bias must be undertaken before owl-pellet data can be used for comparison of mammal community structure among sites, or for monitoring a site over a period spanning a change in the individual owls that are depositing pellets at that site.

Australian Journal of Zoology: 60th anniversary

This year marks the 60th anniversary of Australian Journal of Zoology. To celebrate, we are making a few changes to the journal. We recognise that both zoological research and publishing have changed significantly since 1953, when the journalwas firstlaunched,andthatthejournalmustadapttomeet the requirements of authors and readers. As a result, Australian JournalofZoologyhasnowintroducedseveralnewarticletypes, launched an award to recognise student work, and reaffirmed its commitment to publishing high-quality research. Inadditiontooriginalresearcharticlesandcriticalreviews,we now welcome the submission of several new article types. A series of ‘opus’ reviews, invited from senior zoologists by the editors, will complement current content by providing both retrospective and prospective examinations of the authors’ own research areas. The editors will also commission ‘perspective’ articles–similartoreviews,butthatallowauthorsthefreedomto present thought-provoking ideas, develop novel hypotheses and speculate on controversial topics. Wewillalsoencouragethesubmissionofshorterpapers,such asthosedescribinginnovativezoologicalmethodsortechniques, naturalhistoryobservationsorprimernotes.Fewjournalsprovide aforumforsuchreports,yettheyareoftenimportantobservations that are worthy of wider dissemination. To recognise and celebrate the important student contribution to zoological research in Australia and worldwide, Australian Journal of Zoology has launched the Best Student Paper Award. This award is presented annually for the best original research publicationarisingfromstudentwork(Honours,MastersorPhD) in the most recent volume of the journal. A panel of editors assesseseligiblepapersontheirinternationalimpactinzoological research using Australasian animals. Our first winner is Rohan Bilney from Deakin University for his paper ‘Reversed sexual dimorphism and altered prey base: the effect on sooty owl (Tyto tenebricosa tenebricosa) diet’, from volume 59 of the journal (2011; pp. 302–311). A profile of Dr Bilney and his work will appear in the journal later this year. The journal has always endeavoured to publish high-quality research, quickly and efficiently. Last year, we adopted ScholarOne as our online manuscript handling system – we expectittoimprovethesubmissionexperience forauthorsandto streamline peer review. We strive to reduce editorial turnaround times and aim to return the first decision on most manuscripts within 21 days of submission. As soon as manuscripts are accepted, they are listed online as ‘Just Accepted’ and move straight into production; when ready, they are published Online Early before print publication. Our goal is to publish all papers online within 6 weeks of acceptance. The editorial team and journal staff hope that these changes improve authors’ and readers’ experiences with Australian JournalofZoology.Asalways,wewelcomeyourfeedbackonthe journal and its development, and we look forward to receiving your best work.

Spatial ecology of Sooty Owls in south-eastern Australian coastal forests: implications for forest management and reserve design

We investigated the home-range size and habitat use of eight Sooty Owls (Tyto tenebricosa tenebricosa) in coastal forests in East Gippsland, Victoria, Australia, between November 2006 and January 2008. The size of home-ranges varied widely; based on 95% adaptive kernel estimates, the average size of home-ranges of males was 3025 ha (±1194 s.d., n = 3), whereas that of females was 994 ha (±654 s.d., n = 5). Sooty Owls utilised a broad range of ecological vegetation classes and topographical features for roosting and foraging at a greater scale than previously assumed. There was minimal selection for habitat types based on floristic composition, primarily only avoiding heathlands (for foraging and roosting) and selecting particular dense foliage (rainforest and riparian scrub) for foliage roosting. Two Owls maintained home-ranges close to logged areas, with logging regrowth (<45 years old) being strongly avoided by both individuals. We recommend that the size of individual reserves for Sooty Owls in commercial forests should be increased to more closely resemble the core spatial resource requirements needed by a pair. Reserves should be largest where they feed predominantly on hollow-dependent prey. Most importantly, rather than conservation measures just focussing on the spatial requirements of Sooty Owls, efforts should be directed towards retaining high densities of crucial resources, such as hollow-bearing trees and mammalian prey species throughout the landscape.

Potential competition between two top-order predators following a dramatic contraction in the diversity of their prey base

Abstract Two sympatric native top-order predators, the sooty owl (Tyto tenebricosa tenebricosa) and powerful owl (Ninox strenua) coexist throughout much of their range in south-eastern Australia. Following European settlement, however, major changes in resource availability for these predators potentially resulted in increased competition, especially for food. This study examined ecological attributes of both species, including intersexual differences in the sooty owl, potential resource partitioning and whether competition may be occurring. Dietary overlap was high between female sooty owls and powerful owls (0.90), compared to overlap between male sooty owls and powerful owls (0.67), with three mammalian species contributing over 74% of their diets. Sooty and powerful owls coexisted throughout the study region, regularly roosting within the same vegetation types, and in similar locations, although microhabitat differences were apparent. Sooty owls displayed aseasonal breeding, although a peak in fledging in spring coincided with powerful owl breeding. Both species exclusively nested in similar size mountain grey gums (Eucalyptus cypellocarpa), however, hollow characteristics differed slightly. Significant divergence along a single niche dimension was not detected between powerful and sooty owls, as they had similar diets, habitat usage and activity times, potentially resulting in competition. Reproductive output was low for both species, however, the degree to which competitive interactions influenced this remains unknown. To minimise potential competition, longterm feral predator control and improved habitat management is recommended to increase the density and diversity of small terrestrial mammals, as this should result in diversification of the sooty owl diet, reducing dietary overlap with powerful owls.

Reversed sexual dimorphism and altered prey base: the effect on sooty owl (Tyto tenebricosa tenebricosa) diet

The ecology and function of many Australian predators has likely been disrupted following major changes in prey base due to declines in distribution and abundance of small mammals following European settlement. This study investigated various aspects of the dietary ecology of sooty owls (Tyto tenebricosa tenebricosa), including sexual variation as they potentially exhibit the greatest degree of reversed sexual dimorphism of any owl species worldwide. Sooty owls are highly opportunistic predators of non-volant small mammals, consuming most species known to exist in the region, so their diet fluctuates seasonally and spatially due to varying prey availability, and is particularly influenced by the breeding cycles of prey. Significant intersexual dietary differences existed with female sooty owls predominantly consuming much larger prey items than males, with dietary overlap at 0.62. The current reliance on relatively few native mammalian species is of conservation concern, especially when mammal declines are unlikely to have ceased as many threatening processes still persist in the landscape. Sooty owl conservation appears inextricably linked with small mammal conservation. Conservation efforts should be focussed towards improving prey densities and prey habitat, primarily by implementing control programs for feral predators and preventing the loss of hollow-bearing trees throughout the landscape.

Underestimated and severe: Small mammal decline from the forests of south-eastern Australia since European settlement, as revealed by a top-order predator

In Australia, numerous small mammal species have suffered extinction or severe declines in distribution and abundance following European settlement. The extent of these declines from forested areas of south-eastern Australia, however, remains poorly understood. In this paper we use sub-fossil deposits of the sooty owl ( Tyto tenebricosa tenebricosa) as a tool for understanding the diversity of the small mammal palaeocommunity. These results are compared to the contemporary sooty owl diet from the same geographical region to investigate the degree of small mammal decline following European settlement. Of 28 mammal species detected in sub-fossil deposits and considered prey items of the sooty owl at the time of European settlement, only 10 species were detected in the contemporary sooty owl diet. Numerous small mammal species have not only recently suffered severe declines in distribution and abundance but have also recently undergone niche contraction, as they occupied a greater diversity of regions and habitats at the time of European settlement. For some species our understanding of their true ecological niche and ecological potential is therefore limited. The species that underwent the greatest declines occupied open habitat types or were terrestrial. The severity of decline is also likely to have resulted in severe disruption of ecosystem functions, with wide scale ecosystem consequences. There is an urgent need to improve small mammal conservation, to maintain crucial ecosystem functions performed by small mammals. It is recommended that broad-scale exotic predator control programs are conducted which may also provide suitable conditions for the re-introduction of locally extinct species.

Change in the diet of sooty owls (Tyto tenebricosa) since European settlement: from terrestrial to arboreal prey and increased overlap with powerful owls

The current diet of the sooty owl (Tyto tenebricosa) was determined by analysing freshly regurgitated pellets collected beneath their roosting sites in East Gippsland, Victoria. Comparisons were then made with: (i) prehistoric and historic diet from bone deposits found in cave roosts, and (ii) diet of a sympatric owl species, the powerful owl (Ninox strenua). Sooty owls consumed a large array of terrestrial mammal species before European settlement, but only three terrestrial species were detected in their current diet, a reduction of at least eight species since European settlement. To compensate, sooty owls have increased their consumption of arboreal prey from 55% to 81% of their diet. Arboreal species are also a major component of the powerful owl diet and this prey shift by sooty owls has increased dietary overlap between these two species. Predation by foxes (Vulpes vulpes) and other feral species is likely to have reduced the amount of terrestrial prey available to sooty owls since European settlement. Investigation of changes in the diet of sooty owls may offer a unique monitoring system for evaluating the ability of fox-control strategies to influence increases in numbers of critical-weight-range mammals.

Fauna habitat modelling and mapping: A review and case study in the Lower Hunter Central Coast region of NSW

Abstract Habitat models are now broadly used in conservation planning on public lands. If implemented correctly, habitat modelling is a transparent and repeatable technique for describing and mapping biodiversity values, and its application in peri‐urban and agricultural landscape planning is likely to expand rapidly. Conservation planning in such landscapes must be robust to the scrutiny that arises when biodiversity constraints are placed on developers and private landholders. A standardized modelling and model evaluation method based on widely accepted techniques will improve the robustness of conservation plans. We review current habitat modelling and model evaluation methods and provide a habitat modelling case study in the New South Wales central coast region that we hope will serve as a methodological template for conservation planners. We make recommendations on modelling methods that are appropriate when presence‐absence and presence‐only survey data are available and provide methodological details and a website with data and training material for modellers. Our aim is to provide practical guidelines that preserve methodological rigour and result in defendable habitat models and maps. The case study was undertaken in a rapidly developing area with substantial biodiversity values under urbanization pressure. Habitat maps for seven priority fauna species were developed using logistic regression models of species‐habitat relationships and a bootstrapping methodology was used to evaluate model predictions. The modelled species were the koala, tiger quoll, squirrel glider, yellow‐bellied glider, masked owl, powerful owl and sooty owl. Models ranked sites adequately in terms of habitat suitability and provided predictions of sufficient reliability for the purpose of identifying preliminary conservation priority areas. However, they are subject to multiple uncertainties and should not be viewed as a completely accurate representation of the distribution of species habitat. We recommend the use of model prediction in an adaptive framework whereby models are iteratively updated and refined as new data become available.

Modelling landscape distributions of large forest owls as applied to managing forests in north-east Victoria, Australia

A landscape approach was taken to modelling distributions of large forest owls and conserving habitat for them in 1.2 million ha of forest on the Great Dividing Range in north-east Victoria, south-eastern Australia. Owls were surveyed using call playback at 472 sites, selected by stratified random sampling from geographical information system (GIS) data. Habitat data were collected at each site and at four spatial scales from GIS data. Six owl species were recorded in or near the study region. Data on powerful owls ( Ninox strenua) and sooty owls ( Tyto tenebricosa) were modelled using logistic regression, and predicted probabilities of occurrence were mapped using GIS. Mapped variables explained more variation than habitat variables assessed at survey sites. Powerful owls were most likely to be observed at sites with mature dry forest, many live hollow-bearing trees, diverse habitats within 2 km, and not much pure regrowth within 5 km. Sooty owls were most likely to be observed at sites with wetter more senescent forest associated with tree-ferns ( Cyathea australis and Dicksonia antarctica), blanket-leaf ( Bedfordia arborescens) and silver wattles ( Acacia dealbata), diverse habitats within 500 m and much senescent forest within 5 km. The models were field-tested and found to discriminate well between high and low probability sites. Actual records and then models were used to help select 225 protected areas for large owls, each of approximately 500 ha.

Distribution of nocturnal forest birds and mammals in relation to the logging mosaic in south-eastern New South Wales, Australia

Numbers of nocturnal forest birds and mammals were estimated at 200 widely spaced sites in south-eastern New South Wales to determine their distribution in relation to logging. The focus was on the logged-unlogged forest mosaic rather than on individual logged or unlogged patches. This approach, which compared large areas of unlogged forest with large areas of forest occurring within a logged-unlogged mosaic, was expected to provide more biologically meaningful results, particularly for species with large home ranges. Sampling sites were stratified by geology, within a specified range of mean annual rainfall, and by logging history. Analyses also considered the role of elevation, predominant vegetation community and the proportion of the surrounding landscape which had been logged. All species, with the exception of the greater glider Petauroides volans, were recorded as frequently or more frequently in forests growing on Ordovician sediments. These forests, compared with those on Devonian granites, typically occurred at lower elevations in the region. Multivariate analysis of landscape components suggested that elevation and predominant vegetation community were better predictors of animal occurrence than geology. Logging history appeared to have less influence on counts for most species than geology and/or elevation. The status of many species of nocturnal forest animals is reported in relation to the current logged-unlogged forest mosaic in south-eastern New South Wales. The species having the strongest association with unlogged forest was the greater glider. Numbers of the two largest species of forest owls, the powerful owl Ninox strenua and the sooty owl Tyto tenebricosa, were not disadvantaged at the landscape scale by the current pattern of logging. Our findings indicate the need for maintenance and strengthening of management prescriptions designed to retain and protect unlogged forest in gullies which is recognised as important habitat for most species. Some species, particularly the powerful owl, sooty owl, masked owl Tyto novaehollandiae, greater glider and the yellow-bellied glider Petaurus australis, are likely to require careful management during the second half of the first cutting cycle when adjacent unlogged coupes are cut.

Arboreal marsupials and nocturnal birds in thinned regrowth, unthinned regrowth and old lowland forest, East Gippsland, Victoria

Summary The density and distribution of arboreal marsupial and nocturnal bird fauna in thinned regrowth, unthinned regrowth and old lowland forest was examined. The presence of each species recorded is influenced by the structure and species composition of the forest. Significantly higher densities of arboreal marsupials requiring hollows and undisturbed mixed eucalypt forest (Yellow-bellied Glider, Mountain Brushtail, Sugar Glider) were recorded in old forest. These species are substantially reduced in number in thinned forest. Conversely, thinned and unthinned regrowth is utilised by a range of nocturnal birds (Sooty Owl, Southern Boobook), with many smaller species (nightjars) increasing in number in thinned forest. The retention of some proportion of old trees in regrowth forest or in close proximity, is seen as critical to the maintenance nocturnal bird and arboreal marsupial species in regrowth forest. This study represents a preliminary investigation. Long term monitoring of these sites will be necessary to determine how these species and groups respond to changes in the forest after thinning, particularly if overwood and remnant stags are removed.

The Diet of the Sooty OwlTyto tenebricosain the Blue Mountains, N.S.W.

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Restricted range of ocular accommodation in barn owls (Aves:Tytonidae)

In an examination of the focusing abilities of 15 species of owls, the North American barn owl, Tyto alba pratincola (Bonaparte 1838), was an outstanding accommodator, having a range of accommodation exceeding 10 diopters (Murphy and Howland 1983). Using comparable methods, we examined the accommodation of 4 specimens of the Australian barn owl, Tyto alba delicatula (Gould 1837). We failed to elicit accommodation greater than two diopters, and most stimuli failed to evoke any discernable accommodation at all. Furthermore, examination of other Australian tytonid owls, the grass owl, T. longimembris, the sooty owl, T. tenebricosa, and both the mainland and Tasmanian subspecies of the masked owl, T. novaehollandiae novaehollandiae and T. novaehollandiae castanops, also failed to reveal anything but very moderate accommodative ranges. We conclude that the outstanding accommodative ability of the American barn owl is truly an exception to the modest accommodative abilities of the tytonid owls generally.

Some Field Notes on the Sooty Owl

Some Field Notes on the Sooty Owl