Jerry Olsen

Breeding of the Peregrine Falcon Falco peregrinus. III. Weather, Nest Quality and Breeding Success

Olsen, P.D. & Olsen, J. (1989). Breeding of the Peregrine Falcon Falco peregrinus: III. Weather, nest quality and breeding success. Emu 89, 6–14.Peregine Falcons laid clutches at 75% of territories...

A new Ninox owl from Sumba, Indonesia

Abstract Since the late 1980s ornithologists have reported an unknown Otus owl from the island of Sumba, Indonesia. From a specimen of this unknown owl we analysed the mitochondrial cytochrome b gene in feathers and compared its sequence with those in our data library, which includes most owl genera. A phylogenetic analysis unequivocally places the unknown owl into the Ninox clade. It differs from N. novaeseelandiae and N. scutulata by 8.2 and 9.1% nucleotide substitutions, but our Ninox data set contains few representatives so we cannot define to which other Ninox species it is most closely related. There was no overlap in measurements of body length or mass for this specimen and those of other Ninox known from this region. The call of this new owl was a monosyllabic hoot repeated about every three seconds and quite unlike the repeated ‘cluck-cluck-cluck’ made by the endemic N. rudolfi or the disyllabic notes made by most Ninox, including others in the region. For this new species we assign the common name Little Sumba Hawk-Owl. The conservation status of this owl has yet to be determined, but the species might be threatened and we propose it as Data Deficient.

Trophic relationships between neighbouring White-bellied Sea-Eagles (Haliaeetus leucogaster) and Wedge-tailed Eagles (Aquila audax) breeding on rivers and dams near Canberra

Abstract The diet of the White-bellied Sea-Eagle (Haliaeetus leucogaster) in Australia is poorly known, especially inland. The diet of the Wedge-tailed Eagle (Aquila audax) is better known, but the overlap in prey used by the two eagles has not been studied. In four inland territories of White-bellied Sea-Eagles, and five territories of Wedge-tailed Eagles nesting close to them (range 1.6-5.1 km apart) between July 2002 and December 2004, we identified 116 and 118 prey items from nests of White-bellied Sea-Eagles and Wedge-tailed Eagles respectively. There was little overlap between the diets, and that of Wedge-tailed Eagles was similar to that reported elsewhere. In addition to fish, White- bellied Sea-Eagles specialised in aquatic birds, such as cormorants, grebes or ducks, and aquatic reptiles, such as turtles or water dragons, but tended to avoid terrestrial birds and reptiles, such as ravens and skinks, or mammals such as European Rabbits (Oryctolagus cuniculus) and macropods that were the main prey of nearby Wedge-tailed Eagles. Though food niche breadth was almost identical for the two eagles, Wedge-tailed Eagles captured significantly larger prey, as indicated by the geometric mean prey weight. Our results indicate that closely located breeding pairs of riparian Wedge-tailed Eagles and White-bellied Sea-Eagles were not competing for food, owing to the differences in foraging preferences, at least during the breeding season. We found no evidence to support the claim that the spread of rabbits assisted the increase of breeding numbers of White-bellied Sea-Eagles.

Growth and Development of Nestling Brown Goshawks Accipiter Fasciatus, with Details of Breeding Biology

The nesting chronology of one captive (5 nestings) and two wild pairs of Brown Goshawk Accipiter fasciatus, and the growth and development of twelve captive-bred and five wild-bred nestlings are described. Nest building commenced three to four weeks before egg-laying and involved both partners. Moult in the female started, at the innermost primary, about five days before the first egg was laid. Clutch size was two to four (median 3) and eggs were laid at two to four day intervals (median 2) with incubation usually commencing with the second egg. Incubation, by both sexes, lasted thirty days (range 29-31). amongst the shortest recorded for accipiters. Nestlings hatched in a coat of sparse white down which was gradually replaced by a thicker, browner, down by twelve days of age. At six days wing pins had emerged and at eight days tail pins. Fledging occurred at thirty to thirty-one days (range 28-37). Males usually reached various developmental and plumage stages a day or so before females. Wing length increased linearly between the emergence of the wing pins and thirty-five days of age and gave the best estimate of age. Weight increase was more or less sigmoid; adult weight was reached by fledging in males and slightly after fledging in females. Females were not consistently separable from males by weight until about three weeks of age, and their wing and tail length were similar to those of males until about seven weeks of age. Some methods for the estimation of age and sex are given. Growth rates were rapid in relation to body size.

A brood-size manipulation experiment with Peregrine Falcons, Falco peregrinus, near Canberra

Abstract Brood sizes of Peregrine Falcons in south-eastern Australia were manipulated to examine the effects on parental foraging effort and offspring growth rate. In broods enlarged by one, nestling growth rates were not affected but parents responded by bringing larger prey species and more biomass than did parents of control or reduced broods. Prey size and biomass decreased for the reduced brood. We conclude that parents appeared to increase hunting efforts to meet greater demands for food, and decrease hunting efforts for the reduced brood, but that direct observation of hunting behaviour by colour-marked and radio-tagged Peregrine Falcons with enlarged, reduced, and natural broods is necessary to determine how parents respond.

DIetary Shifts Based Upon Prey Availability in Peregrine Falcons and Australian Hobbies Breeding Near Canberra, Australia

ABSTRACT We collected prey remains and pellets at 16 Peregrine Falcon (Falco peregrinus) nest territories (975 prey items from 152 collections) and one Australian Hobby (F. longipennis) territory (181 prey items from 39 collections) during four breeding seasons in two time periods: 1991–1992 and 2002–2003, a total of 60 peregrine nest-years and three hobby nest-years. By number, European Starlings (Sturnus vulgaris) were the main prey taken by both falcons in 1991–1992 and 2002–2003, but starlings made up a smaller percentage of the diet by number in the latter period, apparently because their numbers had declined in the wild. Although the geometric mean of prey weights and geometric mean species weights were similar in the two time periods, both falcons compensated for the decline in European Starlings in the latter period by taking a greater variety of bird species, particularly small numbers of mostly native birds, rather than taking more of one or two other major prey species. Peregrines took 37 bird species in the latter period not found among their prey remains in the earlier period, and more individuals of some large species such as Gang-gang Cockatoos (Callocephalon fimbriatum), Galahs (Cacatua roseicapilla), and Rock Pigeons (Columba livia). Prolonged drought and competition from increasing numbers of Common Mynas (Acridotheres tristis) may have caused European Starlings to decline, but neither falcon species compensated by catching Common Mynas, even though they are of optimal prey size. Though both falcons, especially peregrines, took the more common bird species found in surveys in the Australian Capital Territory, both tended to avoid large or dangerous species, or agile species that foraged close to cover, such as Common Mynas.

Observations on the Diet of the Australian Kestrel Falco Cenchroides

The diet of the Australian Kestrel Falco cenchroides was studied from castings and remains of food collected during nesting, from contents of digestive tracts and from castings collected during a plague of mice. Spiders, centipedes and, in particular, insects were taken in large numbers and composed most of the diet by number. Grasshoppers and crickets, followed by beetles and moths in various developmental stages, were the most common and regular insects. Small reptiles, small birds and mice made up the vertebrate component of the diet. Mice became the major prey during a plague.

Is wedge-tailed eagle, Aquila audax, survival and breeding success closely linked to the abundance of European rabbits, Oryctolagus cuniculus?

Abstract 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.

A new subspecies of Short-toed Snake-eagle from Wallacea determined from morphological and DNA comparison

The taxonomic status of the geographically isolated population of Short-toed Snake-eagle Circaetus gallicus on the Lesser Sundas (=Nusa Tenggara) has been controversial. In the past they have been regarded as either a migrant population or a recently arrived resident population. Here we obtained DNA sequences from the mitochondrial cytochrome-b gene and combined genetic data with assessments of published and novel morphological data to clarify the taxonomic status of the Lesser Sundas population of C. gallicus. The cytochrome-b distance between the Lesser Sundas and Palearctic populations of C. gallicus is consistent with subspecific differentiation, indicating a possible divergence during one of the most recent Pleistocene glaciations. Although some of the morphological distinctions show overlap, the new subspecies can generally be diagnosed from nominate C. gallicus gallicus by being smaller and paler, and exhibiting less spotting and barring. Unlike nominate populations from mainland Eurasia, the new subspecies seems to lack pronounced sexual dimorphism. We here describe this new subspecies to science and discuss its biology and conservation status.