Nutritional and physiological constraints on reproduction in the endangered swift parrot, Lathamus discolor
Creators: name: Gartrell, Brett David
Publisher: name: University Of Tasmania
Year: 2023

description: This thesis documents my investigations into the factors that constrain reproduction in the endangered swift parrot, Lathamus discolor. First, I have described the annual cycle of reproduction in the swift parrot, by examining changes in the gonads and reproductive hormones (oestradiol and testosterone) of both captive and wild birds. Reproductive development in wild swift parrots initiated after the birds migrated to their breeding grounds in Tasmania from the mainland of Australia. Male swift parrots commenced testes development and increased the plasma concentration of testosterone in all years of the study regardless of the foraging resources available. Reproductive activity in male birds peaked in October and November and gonadal regression occurred in late December and January associated with the development of moult. However, in this period very few female swift parrots were reproductively active. The female swift parrots' initiation of breeding appears to be the major factor limiting reproduction in wild swift parrots. Further, the female birds appear to be limited in numbers as well as opportunities to breed. There is a male sex bias (1.9:1) to the wild swift parrot population based on the examination of birds killed in window strikes and birds trapped by mist-netting. The origins of the sex bias were not determined. In captive swift parrots, I examined the period of reproduction that- encompasses egg laying, egg incubation and chick-rearing. The male swift parrot is solely responsible for the provision of resources to the female during incubation and, in the first two weeks after hatching, to the female and the chicks. This period appears to be a bottle-neck for food resources in the swift parrots' life history. To Maintain the high demand for food resources, nesting must occur in close proximity to good foraging resources. Next, I investigated links between reproduction and nutrition in swift parrots. I examined the morphological adaptations to nectarivory that have evolved in the birds, the food resources used in the breeding season and their ability to extract protein from ingested pollen; all provide evidence for the importance of the flowering of the Tasmanian blue gum, Eucalyptus globulus, to supporting the nutritional requirements of reproduction in swift parrots. I commenced feeding trials in captive birds to examine links between reproduction and dietary energy and protein. However, these trials were disrupted by deaths due to renal disease, which was worsened by high protein diets. Assessment of plasma concentrations of uric acid suggests that swift parrots may have lower protein requirements than granivorous parrots. Finally, I assessed the constraints that migration may impose on reproduction, and the causes of mortality in swift parrots during the breeding season. No physiological preparations for migration were identified in swift parrots. However, behavioural changes associated with migration were identified suggesting that migration limits the time available for reproduction and its timing within the year. Mortality related to collisions with artificial structures, such as windows, fences and automobiles was identified as a threatening process of increasing importance to the swift parrot population. This study has major implications for the conservation of the endangered swift parrot and suggests promising avenues for future research. Further, it highlights the paucity of knowledge of the Australian avifauna and the need for scientific involvement in the management of endangered species.