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Nutritional and physiological constraints on reproduction in the endangered swift parrot, Lathamus discolor


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Gartrell, Brett David 2001 , 'Nutritional and physiological constraints on reproduction in the endangered swift parrot, Lathamus discolor', PhD thesis, University of Tasmania.

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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.

Item Type: Thesis - PhD
Authors/Creators:Gartrell, Brett David
Keywords: Swift parrot, Swift parrot
Copyright Holders: The Author
Copyright Information:

Copyright 2001 the Author – The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2002. Includes bibliographical references

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