Aspects of the biology of the Australasian harrier (Circus aeruginosus approximans Peale 1848) : a thesis presented for the degree of Master of Science by thesis only in Zoology at Massey University

The study is based on 18 months intensive field-work during which 212 Australasian harriers were trapped, retrapped, measured, sexed, aged, individually marked and observed. Fortnightly observations of the individually marked population were made over a further seven months. The Australasian harrier and European marsh harrier are considered to be conspecific. Evidence is presented showing that there is no valid reason for considering Circus aeruginosus of the Pacific Islands to be a different subspecies from C. aeruginosus of Australia and New Zealand. During the breeding season ten territories in the 12 km 2 study area averaged 31 ha, nest sites averaged 910 m apart, pairs' overlapping home ranges averaged 9 km. 2 and favourite hunting areas 3 km, 2. A high population density of one bird per 50 ha was calculated. A low fledging success rate of 1.8 young per successful pair and 1.1 young per nest site, and two cases of polygyny were recorded during two breeding seasons. Territorial and courtship behaviour, nest parameters and the parental division of labour is described. Seasonal movements and the dispersion of all age and sex classes from the study area at the end of the breeding season are described. Most (66.7%) individually marked adults returned after the autumn dispersal phase and established winter home ranges averaging 9 km. 2 . The home range of an adult female in open farmland was calculated to be 14 km 2 using radio-telemetry techniques. A non-breeding season population density of one bird per 80 ha was calculated. Communal roosting, which occurred throughout the year, is discussed. Four hundred and seventy food items were identified in the diet from pellets, prey remains, stomach contents and field observations. In descending order of numerical importance in the diet were mammals (46.4%), introduced passerines (29.0%), insects (7.6%), game birds (6.7%), birds' eggs (4.8%) and aquatic prey (4.6%). Australasian harriers ate significantly greater numbers of live prey than carrion annually. Adults took significantly greater numbers of agile food items than juveniles. Females ate significantly more large (>200 g) and fewer agile food items than did males. Seven search techniques and five attack techniques, including some buteonine techniques, are identified and described in the Australasian harriers' wide range of hunting techniques. Ninety five attacks on prey are recorded and 15.8% of these were successful. Adults were significantly more successful hunters than juveniles. Co-operative hunting, hunting in the daily cycle, feeding behaviour at carrion, interspecific competition for carrion, interspecific disruption of hunting and prey escape tactics are described. From a computer analysis of hunting behaviour data it is concluded that adult males are more manoeuverable and less conspicuous than adult females and juveniles because they flew significantly lower and faster. Adult males also hunted, to a significantly greater degree, those habitats where there were greater numbers of agile prey. The hunting inexperience of juveniles was quantified. The Australasian harrier is moderately sexually dimorphic. Current hypotheses proposed to explain the degree of sexual dimorphism in raptors and why the females of most raptor species are larger than males are critically reviewed

Livestock production land and conservation areas play a complementary role in the conservation of a critically endangered grassland bird

Abstract In many parts of the world, livestock production and biodiversity conservation are important land uses of native grasslands in agricultural landscapes. Approaches to managing grasslands typically differ between production farms and conservation areas as they have different goals. Such differences may have consequent effects on the spatial and temporal habitat suitability for grassland fauna. In semi‐arid grasslands of south‐eastern Australia, the critically endangered Plains‐wanderer (Pedionomus torquatus) is a grassland habitat‐specialist bird that can occur on land managed for livestock production and conservation, but it is unclear if, and when, habitat suitability is affected in each land‐use type. Here, we investigate how land‐use type (livestock production, conservation) and rainfall (preceding accumulated rainfall) affect habitat suitability for the Plains‐wanderer using 11 years of bird occurrence and remotely sensed habitat structure data. We found habitat suitability for the Plains‐wanderer was driven by an interaction between land use and rainfall, with conservation areas supporting larger areas of preferred habitat structure during dry periods but less during wet periods. By contrast, Plains‐wanderers were more likely to occur on livestock production farms during wet periods. We speculate this is because higher grazing pressure on livestock production farms was able to limit biomass accumulation and, hence, maintain more areas of preferred habitat structure. Our findings show that land used for livestock production can complement conservation areas by providing preferred habitat for the Plains‐wanderer during climatic periods that promote grass growth. Furthermore, we highlight that land use and climate are important temporal drivers of grassland dynamics, and approaches to biodiversity conservation should consider how patterns of habitat suitability may shift across landscapes over time. Strategic, landscape‐scale planning and effective agri‐environmental initiatives will be critical to the future of grassland birds such as the Plains‐wanderer

A Framework to Predict the Effects of Livestock Grazing and Grazing Exclusion on Conservation Values in Natural Ecosystems in Australia

Grazing by domestic livestock has greatly degraded many Australian ecosystems and its legacy will be long-lasting in many areas. Although livestock are usually removed from conservation reserves because they are perceived to be incompatible with the conservation of natural ecosystems, they have been retained in several reserves in south-eastern Australia as a management tool to achieve conservation outcomes. These cases highlight the fact that no framework currently exists to address the question, under what circumstances (and in what ecosystems) is livestock grazing - or the removal of grazing - likely to have positive, negative, neutral or uncertain impacts on the diversity and composition of native plants? This paper provides a conceptual framework to predict the effects of livestock grazing and grazing exclusion on the conservation values of native vegetation across natural ecosystems in Australia. It should prove equally relevant to other ecosystems around the world which have evolved without heavy grazing by large herbivores. The framework is based on disturbance- and grazing-ecology literature from Australia and elsewhere, and incorporates the following six main factors: (1) impacts of livestock grazing on soil and ecosystem processes, (2) historical exposure to grazing, (3) site productivity, (4) relative palatability of dominant species, (5) species-specific factors influencing plant recruitment and (6) spatial scale and landscape context. These factors are integrated into a decision tree to describe the potential impacts of livestock on native vegetation in a particular area. Livestock grazing is likely to have detrimental impacts on conservation values in many ecological contexts, especially in relatively intact, uninvaded ecosystems on unproductive soils. By contrast, it may be a useful management tool to achieve conservation objectives where it either (1) controls the biomass of existing potentially dominant, grazing-sensitive plants (native or exotic), (2) prevents encroachment by undesirable, grazing-sensitive, potential dominants, (3) provides disturbance niches required by rare or significant plant species, (4) maintains fauna habitat structure or (5) enhances the diversity of species and vegetation structures across the landscape, especially when most of the landscape is ungrazed. In many cases, other disturbance regimes (especially burning) may achieve similar outcomes; however, other disturbances will not necessarily be more effective than grazing per se, especially in degraded or invaded areas. The framework provides a coarse-level filter to inform management decisions and to allow the findings from individual studies to be placed in a larger ecological context. Although the framework is intended to improve decisions about conservation management, it is clear that much more research is needed to assess the role of grazing exclusion in previously grazed ecosystems, and that modifications to current grazing regimes require testing, perhaps by using adaptive management principles, to ensure optimal outcomes for biodiversity conservation