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The breeding biology of the flesh-footed shearwater Puffinus carneipes

Powell, Christopher D.L. (2004) The breeding biology of the flesh-footed shearwater Puffinus carneipes. PhD thesis, Murdoch University.

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The Flesh-footed Shearwater Puffinus carneipes, a 625g ([plus-minus] 3) shearwater, was studied on Woody Island, off the southern coast of Western Australia, from 2000 to 2003, mainly during the chick-rearing phase. Flesh-footed Shearwaters arrive back at their breeding colony at the end of September/early October, dig burrows and court in October, before an unsynchronised pre-laying exodus through November. Eggs are laid in the last week of November, incubated in December and January, and then hatch mid- to late-January. The fledglings depart in late-April/early-May.

Most nesting burrows were located in areas where soil depth was greater than 350mm ([plus-minus] 14), and were angled into a slope so that the average length was about 1050mm ([plus-minus] 16) long. Burrow activity, monitored with knock-down barricades, peaked around 83-86% of burrows visited nightly in late-October/early-November. Nightly visitation of burrows fell to 8-10% in the third week of November (the pre-laying exodus), and then rose rapidly to around 70% through late-November/early-December as laying commenced. Body mass was high 632g ([plus-minus] 5) during courtship, fell just before the exodus 606g ([plus-minus] 6), then rose again 620g ([plus-minus] 11) upon return.

Parents incubate their egg alternately, each undertaking a shift of one to eight days. A few days after hatching, the nestling is left unattended by day in the burrow, where it receives a meal weighing 13-18% adult body mass every 1.4 nights, on average, during the 101 days ([plus-minus] 1) it spends there. Flesh-footed Shearwaters are strictly nocturnal visitors to their colony, although nightly proportions of nests entered were not adversely influenced by bright moonlight, climatic or oceanographic conditions. Initially, nestlings received small overnight feeds, but these increased in size and were delivered more frequently as nestlings grew. In consequence, although mean peak body masses attained by nestlings differed significantly between years, after an average period of 66 days ([plus-minus] 2) in the nest young attained masses equivalent to 135-160% mean adult mass. This coincided with deposits of body fat, but carcass analyses of nestlings revealed that a substantial proportion of mass accumulation was attributable to water, particularly as a component of body fat.

Subsequently, nestlings lost 30-40% of their mass as the time of fledging approached, even though masses of food were generally no smaller, nor delivered any less frequently during this period. Mass recession occurred primarily as a result of water loss, mainly from the integument, but also, substantially from body fat. This is consistent with the view that mass accumulation is related to feather growth. Although the final body masses recorded differed between years, nestlings fledged at around 92-98% mean adult mass, even though they retained a store of body fat. Nestlings continued to be fed to within one to two days prior to departure. The exception was if the peak mass attained was only 800g or less. Individuals in this low peak mass category lost a proportion of body mass similar to heavier chicks and therefore fledged correspondingly lighter than other fledglings.

It is suggested that parent shearwaters 'over-feed' their nestling so that the peak in body mass coincides with the period of maximum feather growth, and nestling obesity stems from both lipid and water accumulation. The Flesh-footed Shearwater nestling attains a high level of obesity, even though it is fed large meals almost nightly throughout its life ashore, even in poor years. This lends little support to those explanations for nestling obesity in shearwaters that are based upon buffering the young against erratic feeding schedules and long intervals between meals.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Wooller, Ron
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