Penelope Olsen

A statistical methodology for tracking long-term change in reporting rates of birds from volunteer-collected presence–absence data

The ability to track change in biodiversity is essential to guide sustainable management and meet biodiversity monitoring, evaluation and reporting requirements, yet long-term data are usually scarce. Birds Australia has developed a simple survey methodology for use by their nationwide network of volunteers; it involves the collection of data on the presence–absence of species at repeatedly visited sites. Here we present a statistical methodology for use with these binary data to examine long-term change, using as an example records from a major bioregion of eastern Australia, 1999–2007. Regression splines were employed to model trend as a smooth nonlinear function of time within a generalised linear modelling framework. Confidence intervals based on bootstrap resampling provided a basis for assessing the significance of change, and a method was incorporated for identifying important change points in the trajectory from second derivatives of the curve. The methodology proved sensitive to change and the impact of extended dry periods was evident. The populations of several woodland species were found to be in significant decline. Two composite indices to track change common to a group of birds were developed and/or adapted from the existing literature. The results confirm the usefulness of repeated 2-ha presence–absence survey data to provide insight into patterns of long-term trends in bird populations. The statistical methodology described offers a means of tracking trends and identifying important time points and is particularly useful in situations where surveys of presence–absence of species are the most efficient way to gather long-term data.

Parental investment in male and female offspring by the Peregrine Falcon, Falco peregrinus

Abstract There is general theoretical agreement that parents should alter offspring sex ratios in response to the relative costs of producing and raising sexually dimorphic male and female offspring. Among raptors females are often much larger than males, yet there is little skew in nestling sex ratios at the population level. The food intake of male and female Peregrine Falcon, Falco peregrinus, nestlings was compared in order to investigate parental resource allocation to their highly size-dimorphic offspring. Intake of seven broods was measured by (i) counting the mouthfuls nestlings received during a feeding bout, and (ii) by monitoring their turnover of tritiated water, which was combined with the results of an earlier study of four broods. Despite significant differences in size, there was no significant difference in the daily food intake of male and female nestlings for about the first 21 days of the nestling period, after which time growth of males slowed. Females continued to grow and by the end of the nestling period their total weight and food intake exceeded those of males by 45% and 25%, respectively. We argue that many apparent discrepancies between studies on gender differences in food intake can be explained in part by the section of the nestling period that was monitored: any differences may not be apparent until the latter part of the nestling period. The crude growth efficiency of females was greater than that of males. It is concluded that female nestlings require a greater amount of food than do males, but because of greater growth efficiency, they need less than expected on the basis of body mass. A similar pattern was apparent in an interspecific comparison—the difference in food intake between the sexes of the more dimorphic species was less than expected on the basis of direct proportionality. In Peregrine Falcons, there was gender overlap in total food intake over the nestling period. Other studies show that individual nestlings in large broods consume less food than those in smaller broods. Together, these results indicate a wide range of variation in intake for successful growth. Lastly, resource allocation patterns in Peregrine Falcon nests seemed largely determined by sibling interactions. The closest nestling to the adult female during a feeding bout received the most food and no individual monopolised this position, regardless of gender or relative size or age. We propose that a regular supply of large prey to Peregrine Falcon nestlings makes dominance hierarchies unnecessary.

Niche Partitioning by Two Sympatric Goshawks in the Australian Wet Tropics: Ranging Behaviour

Summary Two medium-sized woodland hawks, the Grey Goshawk Accipiter novaehollandiae and the Brown Goshawk Accipiter fasciatus, are sympatric in the Australian wet tropics. Because females are considerably larger than males, the two species and sexes form a four-member guild. Typically, when similar raptor species occur together they partition resources. Radio-tracking was used to study habitat use and composition, and interactions between the Australian goshawks. Sample sizes were small and there was considerable individual variation. Nevertheless, there was evidence of niche partitioning according to home range size and overlap, habitat composition and habitat use. In general, both species frequented forests or woodlands and adjacent open country. Consistent with morphological, dietary and hunting differences, Grey Goshawks, especially the males, frequented closed forest types and Brown Goshawks more open habitats of woodlands, crops and edges. In the non-breeding season, females ranged widely and their ranges overlapped both inter- and intra-specifically, whereas those of males of each species tended not to overlap with males and females of either species. In the breeding season, home range overlap declined markedly between neighbouring pairs of the two species, and there was no overlap between the females. The two species have relatively small home ranges, attributable to their rich habitat. In turn, this may facilitate co-existence of two such similar-sized accipiters. Nevertheless, there was evidence of competition between the two most similar-sized members of the guild, the male Grey Goshawk and the female Brown Goshawk.

Did hybridization save the Norfolk Island boobook owl Ninox novaeseelandiae undulata

The population of the Norfolk Island boobook owl Ninox novaeseelandiae undulata, a nocturnal bird restricted to the Australian territory of Norfolk Island, was reduced to a single female in 1986. Deliberate introduction of two males of its nearest relative, the New Zealand boobook N. n. novaeseelandiae, as a conservation intervention has allowed the taxon to persist on Norfolk Island, albeit in hybrid form. Although declared Extinct in 2000, a re-examination of this unique situation has concluded there is a strong argument that the taxon should be categorized as Critically Endangered because, on average, approximately half the nuclear genome of the original taxon and all the mitochondrial DNA is conserved in all living owls on the island. This thus represents a special case in which the taxon can be considered to be extant, in hybrid form, even though no pure-bred individuals survive. More generally, we suggest that, in exceptional cases, hybridization may not be a threat to highly threatened species and that guidelines are needed to determine when to consider hybrid populations as extant forms of the original taxon, and when to declare extinction through hybridization.

Management of exotic pine plantations in northeast Queensland for goshawks

Summary As a compromise between forestry and wildlife needs, it has been recommended that a mix of native forest and plantation in various stages of succession be integrated to form a mosaic of different forest types. However, lack of detailed biological data on species dependent upon native forest has hampered the development of such an approach. Between 1987 and 1990, we monitored breeding and foraging activity of the Grey Goshawk Accipiter novaehollandiae and Brown Goshawk A. fasciatus in a North Queensland State Forest converted to exotic softwood Pinus caribaea production. Fifty per cent of the area was planted with pine aged between 1 and 9 years old, intermixed with native forest and woodland. The area supported several pairs of goshawks that bred only in large mature trees within native forest or woodland, but often used plantations for hunting where these formed ecotones with other habitats. Based on the results of this study we make the following preliminary recommendations for the conservation of goshawks in areas of managed plantation: (1) forest maintenance should be avoided, particularly around active goshawk nests, during the breeding season, from August to December; (2) an area of 20 ha of native forest should be retained as a buffer zone around any active goshawk nest; (3) woodland and forest along watercourses is particularly important goshawk habitat and a minimum width for riparian buffer zones is considered to be 200 m from the watercourse to the edge of P. caribaea plantations; (4) the ecotone between tall open forest and tall woodland that occurs adjacent to riparian closed forest is an important habitat for breeding goshawks and should be conserved wherever possible; and (5) the 50–50 mix of native woodland/forest and plantation, as at Abergowrie, appears able to sustain viable populations of goshawks, at least in the short-term.