Boobook Ninox Research Articles

Exploiting boom times. Southern Boobook OwlNinox novaeseelandiaediet during a rodent irruption in central Australia

Populations of Australian desert rodents are known to undergo booms in response to resource pulses following periods of high rainfall. Australia's arid-adapted Tyto owls have been recorded responding functionally and numerically to these small mammal booms, though it is not known whether Southern Boobook Ninox novaeseelandiae is able to respond similarly. We aimed to determine whether Southern Boobooks could find and exploit a localised rodent irruption in the western Simpson Desert, in a location with few roost trees and no tree hollows. Boobook owls immigrated to the site from an estimated distance of ≥ 32 km and appeared to be resident over a period of ≥ 4 months, coinciding with a localised irruption of Plains mice Pseudomys australis. Dietary analysis confirmed that the owls specialised on small mammals, with rodent and dasyurid species accounting for c. 98% of prey items and > 99% of prey biomass. There was no evidence of reproductive activity among the owls and they vacated the area as the small mammal irruption subsided. Although a dietary generalist across its range, our results indicate the Southern Boobook is capable of specialising on small mammals during population irruptions.

The Diet of Breeding Brown Falcons (Falco berigora) In the Canberra Region, Australia, With Comparisons To Other Regions

Brown Falcons (Falco berigora) are generalist predators that take prey from a range of different taxonomic groups. Further, this species is one of the most widespread raptors in Australasia, providing great scope for dietary flexibility. However, few studies have reported on the diet of this species, and none in any detail for the relatively dry, continental climate of the Canberra region of southeastern Australia. We therefore examined this species' diet from 29 collections of prey remains and pellets from 20 nesting territories over five breeding seasons of Brown Falcon pairs breeding within 40 km of Canberra in 2002–06 and again in 2009. A total of 307 prey items was recorded, 15 of which were novel for this species. These novel prey items largely reflected locally common species that were of a similar size and niche to prey previously recorded in other regions, such as a new prey species of quail or beetle. Unusual prey included garden snails (Helix aspersa) and an owl, the Southern Boobook (Ninox novaeseelandiae). Other infrequently captured prey items such as freshwater molluscs (Corbicula australis and Glyptophysa gibbosa) and crayfish (Cherax sp.) illustrated the extraordinary dietary flexibility of Brown Falcons. In comparison with previous detailed studies, Canberra-based pairs had a relatively small geometric mean prey weight of 7.7 g, and tended to take a higher proportion of invertebrates across a relatively narrow niche breadth. When biomass was considered, rabbits (Oryctolagus cuniculus) were an important food source, making up half of the total biomass in the diet.

Population densities and conservation status of Norfolk Island forest birds

SummaryThree weeks of intensive surveys in Norfolk Island National Park in 2009 failed to find White-chested White-eye Zosterops albogularis and it was calculated that there was a less than 17% probability that a population of 10 birds had been overlooked. The last multi-observer record of this species was in 1978, and it is recommended that the species’ IUCN Red List status of “Critically Endangered” is tagged as “Possibly Extinct”. During these surveys, the population densities of seven bird species were calculated from 352 independent point counts. Causes of imprecision and bias were investigated, suggesting a small underestimation. Other species were recorded too infrequently, or their distributions were too biased, for analysis. The population densities of the extant endemic taxa were relatively high and suggest no current declines, and the population estimates were consistent with previous studies. This study recommends monitoring most species by point counts, or line transects if resources are limited, supplemented with specific monitoring of Tasman (Norfolk Island) Parakeet Cyanoramphus cookii, Pacific Robin Petroica multicolor, Southern Boobook Ninox novaeseelandiae and seabirds. Ongoing monitoring of these birds is needed to help inform management of the National Park and the island in general, given their small population sizes and their likely susceptibility to rat and cat predation, competition from alien species and drought.

Home-Range Size and Territorial Calling of Southern Boobooks (Ninox novaeseelandiae) in Adjacent Territories

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.

The distribution of three nocturnal bird species across a suburban-forest gradient

On a global scale, urbanisation has a profound effect on the distribution of wildlife. Here we seek to test the effects of urban encroachment on the distribution of three key members of the Australian nocturnal bird community: the Tawny Frogmouth (Podargus strigoides), Australian Owlet-nightjar (Aegotheles cristatus) and Southern Boobook (Ninox novaeseelandiae). The distribution of the species was recorded in three landscape types—suburban, urban-fringe and forest—with the level of urbanisation classified according to attributes at both landscape level and site level. The effects of urbanisation on individual species were determined by a comparison of broad landscape attributes and species distributions. Site-level attributes were modelled to determine their influence on the presence of species. Although all three species occurred in the urban-fringe landscape (50–64% of sites), the presence of the Tawny Frogmouth, a species with more generalist habitat requirements, increased in response to increasing levels of urbanisation. The Australian Owlet-nightjar and Southern Boobook, which have more specialised habitat requirements than the Frogmouth, showed a corresponding decrease in presence to increasing levels of urbanisation. Although all three species appear to tolerate the level of disturbance in urban-fringe environments, these areas are also at risk of further degradation. It is critical that continued research focuses on urban-fringe environments to investigate species-specific demographic responses to urban gradients.

Avian trichomoniasis: a study of lesions and relative prevalence in a variety of captive and free‐living bird species as seen in an Australian avian practice

Studies of avian trichomoniasis in the literature are limited to some extent, often being confined to a single bird species or group of species within a bird Order. Some incidence studies have been reported for free-living birds, and occasionally for captive birds. Very few reports describe the prevalence and types of lesions seen for a wide range of bird species, especially from a clinical perspective. Retrospective study of avian practice records from a 10-year period. Emphasis on the types of presentations and relative prevalence of trichomoniasis in a variety of captive and free-living bird species encountered in Australian avian practice. The occurrence of trichomoniasis in several novel species (lorikeets, corvids and a cuckoo species), plus its distinctive presentation in southern boobook owls (Ninox boobook), is documented. Trichomoniasis should be a differential diagnosis for birds presenting with regurgitation or upper gastrointestinal abscesses, even if motile trichomonads are not found in wet preparations from crop washes or lesions.

A survey of large forest owls in State Forests of south-western New South Wales, Australia

A survey of large forest owls was conducted at 261 survey points within State forests of south-western New South Wales, and an additional 10 sites within the Wagga Wagga Local Government Area in May-June 2004. A combination of listening, playback of recorded calls and spotlighting was used. Barking Owls Ninox connivens were recorded primarily from River Red Gum Eucalyptus camaldulensis vegetation associations (n = 8) and once from mixed Western Grey Box Eucalyptus microcarpa / River Red Gum association. No records of the Powerful Owl N. strenua or the Masked Owl Tyto novaehollandiae were obtained. Four other nocturnal bird species were recorded during the surveys: Southern Boobook N. novaeseelandiae (n = 74), Barn Owl T. alba (n = 61), Australian Owlet-nightjar Aegotheles cristatus (n = 46) and Tawny Frogmouth Podargus strigoides (n = 8). In light of the low frequency of Barking Owls recorded in this and other recent surveys, consideration needs to be given to upgrading the classification of the Barking O...

The diet of a Southern BoobookNinox novaeseelandiaein Box-Ironbark country, central Victoria

The diet of a Southern Boobook Ninox novaeseelandiae in a Box-Ironbark woodland remnant in central Victoria was studied. An analysis of 42.5 pellets found invertebrates to represent 82% of the total prey items, but vertebrates, in the form of the House Mouse Mus domesticus, to represent 88% of the biomass. The proportion of spiders as prey items in the diet in this instance (43%) was significantly higher than in other studies on mainland Australia.

Description of Synhimantus (Dispharynx) Mawsonae N. SP. and ARedescription of Procyrnea Dollfusi (Mawson, 1968) (Nematoda:Spirurida) From the Southern Boobook Owl, Ninox Boobook (Latham,1802) (Aves: Strigidae)

SummarySynhimantus (Dispharynx) mawsonae n. sp. is described from the boobook owl, Ninox boobook (Latham, 1802) (Aves: Strigidae), from New South Wales, Australia. The new species differs from congeners in the number and arrangement of pedunculate caudal papillae, length and shape of spicules, in having straight, only slightly sinuous cordons and in having tricuspid cervical papillae. Procyrnea dollfusi (Mawson, 1968) is redescribed from the type host, N. boobook; new features described are the imbricated cervical cuticle and the ornamentation of the tail of the male. Synhimantus (Synhimantus) laticeps (Rudolphi, 1819) is also reported from N. boobook, confirming original records and extending its geographical range within Australia.

Error rate of axons at the owl's optic chiasm

Background: In owls, the visual pathways from the retina are totally crossed. Attempts to find ganglion cells with uncrossed axons have failed consistently, when retrogade labeling with HRP is used for their identification. In the present investigation we have used retrograde fluorescent tracers of complementary colour in each optic tectum to demonstrate a tiny population of ipsilaterally‐projecting retinal ganglion cells in the owl. Methods: We studied two species, one from each of the two important owl families: the Southern boobook owl, Ninox boobook: (Family Strigidae); and the Barn Owl, Tyto alba: (Family Tytonidae). Results: The small numbers, random distribution and heterogeneity of the mis‐projecting ganglion cells, taken together, argue against a functional role for them. Instead, they appear to be the result of developmental errors in the specification of laterality. At a number of different eccentricities and ganglion cell densities, the error rate was roughly a constant fraction of the neurons involved, at around 10‐4 for the tytonid owl (lacking a fovea) and around 10‐5 for the strigid owl (which has a fovea and a higher overall density of ganglion cells). Conclusions: These values are close to the error rates of replicating enzymes, such as nucleic acid polymerases. The evolution of a higher retinal ganglion cell density and a fovea in the Strigidae appears to be accompanied by an improvement in the error rate.

The diet of Southern Boobooks in South Australia

Gizzard contents from 117 Southern Boobooks, Ninox novaeseelandiae, collected throughout South Australia were analysed for sexual and seasonal differences in diet. Overall, invertebrates made up 95.9% of the diet by numbers. Coleoptera, Orthoptera and Lepidoptera were the most important prey groups ingested. Seasonal differences in the consumption of some prey groups were found, apparently correlated with seasonal variation in the abundance of those groups. Overall, males took more prey than females, and there were significant differences between the sexes with respect to the animals captured.

Impacts of timber harvesting on mammals, reptiles and nocturnal birds in native hardwood forests of East Gippsland, Victoria: a retrospective approach

Summary The occurrence of mammals, reptiles and nocturnal birds was assessed in a series of successional forest sites in East Gippsland, Victoria, Australia. A total of 63 sites, representing three major forest types (Wet, Damp and Lowland) and six different forest age classes (2, 5, 10, 18, 25 y after logging and unharvested), was sampled using a range of census techniques, with each combination of forest type and age class replicated. Totals of five nocturnal bird, twenty mammal and seven reptile species were recorded during this study. Key species were selected for subsequent analysis, representing three major faunal assemblages (arboreal mammals and nocturnal birds, ground-dwelling mammals, and heliothermic reptiles). Generalised linear modelling was used to investigate the relationship between the occurrence and diversity of species within each faunal assemblage with respect to the design variables (forest type and age class). To help explain any observed intra-age-class variation in animal occurrence or diversity, structural attributes were also analysed. The study highlights the importance of retained habitat attributes (old-growth legacies) within logged forest if wildlife conservation is to be a priority. The presence and abundance of large trees were the most important habitat variables for hollow-dependent fauna such as the southern boobook and yellow-bellied glider. The southern boobook and native rodents (Rattus spp.) were most likely to be found in unharvested forest, implying a negative impact of timber harvesting. The black wallaby was the only species to show a preference for younger age classes, an expected response from a species known to browse on regrowth seedlings. The mountain brushtail possum was more likely to be found on smaller coupes. Lowland forest supported the greatest species diversity of ground-dwelling mammals when only the design variables were considered. When effects of tree height and aspect were considered separately in the model, the trend was for greater species diversity in Damp forest. It is recommended that any increase in logging intensity in either Damp or Lowland forest should be balanced with suitable measures to protect sites of high conservation value. In the short term, no single species of heliothermic reptile appeared to be disadvantaged by logging operations. Spencer's skink may benefit from an increase in regrowth forest, provided large retained trees can be used as basking sites above the regrowth canopy. Species diversity of reptiles was affected adversely by harvesting in the Lowland forests and positively in the Wet forests. The protection of microhabitat attributes during timber harvesting operations may be one management strategy that would favour the long-term survival of forest reptiles in a logged area.

The use by wildlife of paddock trees in farmland

Morning and dusk watches at live and dead trees were used to systematically investigate which species of vertebrates use paddock trees within farmland proposed for the establishment of Eucalyptus plantations in northern New South Wales. Tree-watches at 108 trees were stratified on farmland as isolated, in small patches, remnant vegetation and riparian strips plus in adjacent forest. Arboreal marsupials and bats emerged from hollows in 11% and 8% of trees, respectively. Only one colonial bat roost was observed, although the marsupials Trichosurus vulpecula and Petaurus breviceps were widespread in the landscape. Two threatened species of marsupials (Petaurus norfolcensis and Phascogale tapoatafa) were observed using paddock trees on flats or slopes outside of riparian strips. Among owls, only the Southern Boobook Ninox novaeseelandiae and Barn Owl Tyto alba were observed using tree hollows on farmland. For all hollow-dependent nocturnal fauna (marsupials, bats and owls), very large tree diameter best predicted occupation of a tree-hollow (especially if <800 m from the nearest forest). In addition to providing hollows, paddock trees were used for foraging. Morning surveys revealed 35 diurnal bird species on isolated trees, although most were generalists (e.g., Eastern Rosella Platycercus eximius, Noisy Miner Manorina melanocephala) that were also regular visitors to non-isolated trees in remnant vegetation. More forest-dependent and forest-associated bird species were recorded in forests and riparian strips than other tree categories, reinforcing the high conservation value of riparian strips in farmland. After dark, ultrasonic detectors recorded 21 species of bat (seven threatened species) flying in close proximity to paddock trees. Relatively high levels of activity were recorded at one study location for species rarely recorded in forests (e.g., Scoteanax rueppellii). Remnant Eucalyptus tereticornis and E. amplifolia were a significant source of blossom for nectarivores and they were also associated with high bat activity, possibly because they grow on fertile soil. Recommendations on tree retention guidelines are discussed.

Southern Boobooks Report

Southern Boobooks Report

Southern Boobooks or Problems with Identification?

Southern Boobooks or Problems with Identification?

Vocalisations of the Christmas Island Hawk-Owl Ninox natalis: Individual Variation in Advertisement Calls

SummarySix different calls of the Christmas Island Hawk-Owl Ninox natalis were recorded during a two-year study of its biology. These vocalisations showed many structural and functional similarities with those described for the Southern Boobook N. novaeseelandiae. Of 195 advertisement calls by 11 owls, 91.3% were correctly attributed to an individual using a multiple discriminant analysis model comprising five measurements of call frequency and duration. We provide some evidence for the calls of individuals being constant over time. Individual variation in advertising calls may have some use in estimating owl densities, especially in areas where the terrain makes traditional techniques such as radio-tracking impractical.

Southern Boobooks

Southern Boobooks

Re-establishment of an endangered subspecies: the Norfolk Island Boobook Owl Ninox novaeseelandiae undulata

SummaryThe Norfolk Island Boobook Ninox novaeseelandiae undulata is confined to the small, isolated Norfolk Island group, an Australian territory. On morphological and biogeographical grounds, it is here classified as a large, distinctive subspecies of the New Zealand Morepork N. novaeseelandiae. In 1986 only one specimen, a female, survived. A shortage of large trees with suitable nesting holes appeared to be the immediate problem. The Australian Nature Conservation Agency, islanders and New Zealand wildlife authorities have cooperated 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 were introduced. The female paired with one male and produced four hybrid F offspring (in 1989 and 1990). Two of these paired in mid-1991 and have since produced five F offspring (two in 1993 and three in 1994). The original female remains paired but now appears to be reproductively senile. At present there seems to be a shortage of mature males, since two female offspring are paired and both lay eggs and attempt to incubate them in the same nest; and a lone female has established a territory. In early 1995 all eleven owls appeared to be alive in the wild. The effort is low-cost, requires relatively little manpower, is carried out with minimal disturbance to the owls, and goes hand in hand with other conservation programmes.

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.

Pesticide-related Eggshell Thinning in Australian Raptors

Eggshell thickness of 32 species of Australian raptors, relative to DDT use, was investigated. Nine species showed a significant reduction in shell thickness since DDT was introduced to agriculture in 1946: Whistling Kite Haliasfur sphenurus; Brahminy Kite Haliastur indus; White-bellied Sea-Eagle Haliaeetus leucogaster; Marsh Harrier Circus aerugrnosus; Collared Sparrowhawk Accipiter cirrhocephalus; Peregrine Falcon Falco peregrlnus; Grey Falcon Falco hypoleucos: Australian Hobby Falco longipennis; and Southern Boobook Ninox novaeseelandiae. Average reductions in thickness ranged from 2% (Collared Sparrowhawk and Australian Hobby) to 10% (Peregrine Falcon). These levels are unlikely to be causing widespread population declines. However, several clutches from these species were so thin (maximum thinning ranged from 15% for the Grey Falcon to 45% for the Whistling Kite) that they were likely to break during incubation. Thus, localised breakage of eggs and reproductive failure has probably occurred. In general, bird-eating raptors and those living in areas of intensive agriculture were worst affected. Ostensibly, DDT consumption declined from a peak in 1973 to none in 1989. Reduction in shell-thickness occurred as early as 1947 and was greatest throughout the 1970s and 1980s. The uncontaminated eggs of owls were thinner than those of other raptors, perhaps partly reflecting the owls' lower absorption of dietary calcium (bone).