Year

2011

Degree Name

Doctor of Philosophy

Department

Department of Biological Sciences, Faculty of Science

Abstract

Despite the fact that Australia’s savanna is still a highly connected landscape dominated by native vegetation, over a quarter of Australia’s granivorous birds have declined in abundance or experienced range contractions over the last fifty years. It is widely assumed that cattle grazing and changed fire regimes have lowered the quality of savanna habitats for grass-seed eating species by lowering the productivity of important grasses. However, the relative impacts of changed land use on granivores such as finches remains poorly defined because of difficulties in monitoring the abundance of these semi-nomadic birds in remote areas. Consequently, my study compares the health measures of finch populations to determine if the timing and severity of changes in health indicators coincide with differing land management. The relative number of unhealthy animals can indicate a population’s probability of decline, as sick or chronically stressed individuals are less likely to survive and breed. I monitored a variety of finch species in order to describe relative granivore responses to land management. Declining species are characterized by specialized diets, prolonged breeding seasons and strictly timed moulting periods, while non-declining species have opportunistic feeding, breeding and moult strategies which could aid them in responding to the seasonal savanna environment and recent habitat changes in Northern Australia. This led me to hypothesize that health patterns would differ between these species seasonally. Therefore I monitored finches during the peak breeding season, when food resources are plentiful just after the wet growing season, and again in the non-breeding season, when grass seeds become scarce, and most finches are moulting. Based on the theory that grazing and burning lowers the quality of finch habitat, I also hypothesized that finches would show differences in health between populations living in areas of differing land management. Finches were monitored for two years in three study areas in the Northern Territory and three in Queensland; one site per state was conservation managed (without grazing and fire), one was pastoral (grazed but without fire), and one was aboriginal (with frequent burning, but without high grazing). The health of declining Gouldian finches and non-declining Long-tailed and Masked finches were monitored in the Northern Territory while declining Star and Black-throated finches were monitored in Queensland. Health indices included body condition measures (body mass, fat stores and muscle contour), haematocrit and stress response to capture using plasma corticosterone (CORT) and binding globulin levels. Finch habitat was surveyed in the Northern Territory in order to describe any differences in the grass layer in response to grazing or fire and among land tenures. Health monitoring results suggest that all finch species have better body condition during breeding seasons and declining species have a possible pattern of chronic stress during non-breeding seasons. All finch species had higher body mass and muscle scores and lower fat stores during breeding compared to non-breeding. Measures of CORT showed that Gouldian, Star, and Black-throated finches have stress response patterns opposite to that seen in most passerine studies; low stress responses during breeding and high stress during non-breeding. This pattern suggests that declining species are experiencing chronic stress during non-breeding, possibly due to low food resource availability during this time of year. Non-declining Long-tailed and Masked finches had a normal stress response pattern, opposite to declining species. High stress, low body condition and unusually high haematocrit were found in Gouldian finches monitored on pastoral land during a non-breeding season. Gouldian finches surveyed on aboriginal land during this season also had lowered body condition and unusually high haematocrit compared to birds sampled on conservation land. Habitat surveys showed that annual grass cover was low on pastoral land and perennial grass cover and productivity was low on aboriginal land compared to conservation managed land. These low grass measures coincided with the poor health of Gouldian finches on pastoral and aboriginal land, suggesting lowered grass abundance as a likely cause of poor finch health. Though Black-throated finch body condition and haematocrit were similar between land tenures, stress responses were higher on pastoral land compared to conservation managed land during the non-breeding season in 2007. This suggests that Black-throated finches may be sensitive to grazing effects during some years. Star Finches monitored in open grasslands tended to have higher haematocrit levels, suggesting a lifestyle with higher energy demands. No consistent significant differences were found between the health measures of Long-tailed or Masked finches sampled on different land tenures. ix The results of this study suggest that tropical finch species have seasonal health variation which implies poorer condition during non-breeding compared to breeding seasons and a possible pattern of chronic stress in three declining species. This supports my hypothesis that declining species are more sensitive to seasonal changes. Coinciding differences in finch health, land tenure and grass cover estimates suggest that non-conservation management adversely affects finch health and grasses important to finches. This was particularly evident for the declining Gouldian finch and indicates a probability of future finch population declines on non-conservation managed land. Thus this research provides evidence of the threat of intensification of pastoral practices and continued frequent burning to declining savanna species. This study also reveals the utility of using health indices to determine the sensitivity of birds to environmental perturbations.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.