Cook, Australia
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Trost S.,44 Wybalena Grove | Olsen J.,University of Canberra
Australian Field Ornithology | Year: 2016

Over a 30-night period a Common Myna Acridotheres tristis was observed attacking Common Brushtail Possums Trichosurus vulpecula and harassing a female Southern Boobook Ninox boobook near her nest. One night a Myna that had been attacking Possums was chased by the male Boobook, which appeared to be chasing it as prey. We did not observe further attacks by Mynas after this night. Common Mynas were found in the dietary analysis for this pair of Boobooks. © 2016, Bird Observers Club of Australia (BOCA). All rights reserved.


Olsen J.,University of Canberra | Judge D.,University of Canberra | Trost S.,44 Wybalena Grove | Rose A.B.,College Street
Australian Field Ornithology | Year: 2013

The size of prey taken by Powerful Owls Ninox strenua, the relative densities (abundance) of small versus large arboreal marsupials in eucalypt forests, the lack of asymmetrical ears in Ninox owls, and the male's habit of roosting on dead prey during the day may be clues to understanding 'Normal' Sexual Size Dimorphism in large Ninox species, the inverse of the 'Reversed' Sexual Dimorphism found in most owls, hawks and falcons.


Olsen J.,University of Canberra | Judge D.,University of Canberra | Trost S.,44 Wybalena Grove | Rose A.B.,College Street | And 4 more authors.
Australian Field Ornithology | Year: 2011

The diet of three Powerful Owls Ninox strenua in the Australian Capital Territory was studied in 2007. A pair in Namadgi National Park took five Sugar Gliders Petaurus breviceps, a Greater Glider Petauroides volans, birds and a crustacean. Among avian prey, the Bassian Thrush Zoothera lunulata is a new record for Powerful Owls. An Owl at the Botanic Gardens took 41 Sugar Gliders, 10 Common Ringtail Possums Pseudocheirus peregrinus and two juvenile Common Brushtail Possums Trichosurus vulpecula, the last apparently off the females' backs. This Owl was observed perching on prey items on 11.9% of the days it was seen: seven times on Sugar Gliders, twice on Ringtail Possums, and twice on Brushtail Possums. It was seen attacking Sugar Gliders and adult Brushtail Possums, but beak-clacking when attacking the Brushtail Possums (so apparently attacking them as competitors, not prey). It was agile while hunting. Its behaviour was affected by mobbing by diurnal birds. Geometric Mean Prey Weight (GMPW) of Powerful Owl prey (including four items from a previous Namadgi analysis) in the ACT was 176.48 g, and the prey/predator weight ratio was 0.118. GMPW calculated from a previous study in Canberra of Southern Boobooks Ninox novaseelandiae was 2.11 g, and the prey/predator weight ratio was 0.008, much lower than for Powerful Owls. Standardised Food Niche Breadth for Powerful Owls was 0.115, and for Southern Boobooks 0.325; i.e. dietary evenness and richness were much higher for Boobooks. Powerful Owls took 95.2% arboreal marsupials, whereas Boobooks took a wider range of species including a large proportion of insects.


Olsen J.,University of Canberra | Downs J.A.,University of South Florida | Tucker T.,University of Canberra | Tucker T.,Mote Marine Laboratory | Trost S.,44 Wybalena Grove
Journal of Raptor Research | Year: 2011

Adjacent nesting home ranges of four radio-tagged Southern Boobooks (Ninox novaeseelandiae) were studied in a Canberra, Australia, woodland over 418 observation nights during four breeding seasons. Spatial locations and bouts of territorial calling (boobook calls) were recorded during each observation night. Home ranges and core areas were computed from the spatial locations using minimum convex polygons and characteristic hull polygons. Home-range sizes varied by individual owl, between breeding seasons, and by estimation method, ranging from 18.1 to 205.8 ha. Core-area estimates varied from 0.2 ha to 19.6 ha, indicating intensive use of core areas within much larger home ranges. Overall, about 26% of the boobooks' vocalizations occurred within core areas and about 56% within the home range but outside the core area, often near the border shared with the adjacent pair. Approximately 21% of boobook calls were observed on or outside home-range boundaries, which suggested that owls actively defended areas larger than their core areas. © 2011 The Raptor Research Foundation, Inc.


Olsen J.,University of Canberra | Judge D.,University of Canberra | Trost S.,44 Wybalena Grove | Lisle J.,2 Carbeen St
Corella | Year: 2013

In raptors, males are said to deliver most of the prey items during the breeding season. In this study we compared male versus female prey deliveries at eight nests of Southern Boobook Ninox novaeseelandiae in Canberra. We observed the incubation period on 103 nights, nestling /fledging period on 143 nights, for a total of 246 nights. Females hunted through the incubation period. Prey deliveries for males and females combined averaged 8.90 items per hour during the nestling period and 11.04 per hour during the fledging period, in the first hour or two after dusk. In the first half of the nestling period (weeks 1-3) females delivered significantly more prey items per hour than males did (3.44/hour compared to 1.60/hour). Females hunted near the nest and delivered more invertebrates than did males. In the second half of the nestling period, (weeks 4-6), there was no significant difference in the number of prey deliveries between males (5.11 items/hr) and females (5.84 items/hr). For the total nestling period, (weeks 1-6), females made 5.01 deliveries per hour, significantly higher than male deliveries at 3.90 per hour. There was no significant difference in the number of prey deliveries to fledged young by males (5.29/hr) and females (5.75/hr). Both males and females delivered vertebrate prey. These data do not fit the 'normal' pattern of male/female behaviour found in most raptor studies.


Olsen J.,University of Canberra | Cooke B.,University of Canberra | Trost S.,44 Wybalena Grove | Judge D.,University of Canberra
Wildlife Research | Year: 2014

Context Some ecologists argue that nesting success and abundance of wedge-tailed eagles (Aquila audax) are strongly linked to the abundance of introduced wild rabbits (Oryctolagus cuniculus). Consequently, concerns were expressed about eagle population viability when the biological control agent rabbit haemorrhagic disease virus (RHDV) heavily reduced rabbit numbers. However, observations following the spread of rabbit haemorrhagic disease (RHD) in Australia and Spain (where Aquila adalberti is an equivalent of A. audax) question this assertion. Eagle numbers did not fall even though rabbits declined regionally by up to 90% in both countries. Aims To reconsider the assumption of a strong link between rabbit abundance and wedge-tailed eagle breeding and population maintenance. Dispelling misconceptions, if any, about the eagles' dependence on rabbits would benefit the future management of both eagles and rabbits. Methods We reviewed the literature associated with claims that eagles were heavily dependent on rabbits and asked whether these views could be substantiated given the lack of changes in eagle abundance following the spread of RHD. Data on eagle egg-clutch size and nesting success were also reviewed. Conclusions There is little evidence that eagles depend heavily on rabbits as prey. Instead, as rabbits decline, more kangaroos, reptiles and birds are eaten, partly because more native prey becomes available. Eagles have a high proportion of rabbits in their diets mainly where degradation of natural ecosystems, including that caused by rabbits, results in native prey being rare or unavailable. There has been minimal variation in average clutch size following major perturbations in rabbit population size. Implications Rather than perpetuating the idea that high populations of rabbits are needed for wedge-tailed eagle conservation, resources would be better re-directed into understanding continental-scale eagle population dynamics. This would provide a more rational framework to assist decisions on future biological control agents for rabbits. © 2014 CSIRO.


Olsen J.,University of Canberra | Trost S.,44 wybalena Grove | Judge D.,University of Canberra
Corella | Year: 2010

Between 1996 and 1999 we measured the distance from the nest that four Southern Boobooks called using 'territorial boobook' and 'bray' calls, the latter used only by females. Median distances from the nest tree that they used 'territorial boobook' calls were 175 metres and 250 metres for two females, 210 metres and 525 metres for two males. The two females used 'territorial boobook' calls within a 100 metres radius of the nest tree only 12 per cent of the time, the two males only 31 per cent and 0 per cent of the time. Median distances from the nest that both females called using 'bray' calls were 10 metres, range 0-450 metres for one, 0-350 metres for the other. Females used 'bray' calling within 100 metres of the nest 70 per cent and 88 per cent of the time. Territorial boobook' calling was not an effective way of finding boobook nests; 'bray' calls of females more often revealed precise nest locations.

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