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The comparative breeding biology of sympatric crested terns Sterna bergii (Lichtenstein), and Silver Gulls Larus novaehollandiae (Stephens) in south-western Australia

Dunlop, James Nicholas (1986) The comparative breeding biology of sympatric crested terns Sterna bergii (Lichtenstein), and Silver Gulls Larus novaehollandiae (Stephens) in south-western Australia. PhD thesis, Murdoch University.

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This thesis reports an investigation of the double-nesting phenomenon, a unique pattern of anomalous, protracted breeding, reported in seabirds from mid-western and south-western Australia. In particular, it deals with the Crested Tern Sterna bergii Lichtenstein and the Silver Gull Larus novaehollandiae Stephens, two related lariform seabirds which nest in sympatry, and possibly associatively, in the Fremantle area of south-western Australia. Both species have protracted breeding seasons in the study area, superficially similar in timing and duration, and therefore provided useful subjects for a comparative study of their breeding biology.

From 1979 to 1984, the reproductive cycles of the two species were examined in detail. Emphasis was placed on determining the timing and periodicity of breeding, both at the population and at the individual level, and on determining those factors involved in the ’proximate' control of the reproductive cycle. The results showed that, despite superficial similarities in breeding seasons, there were fundamental differences in biology between the two species, particularly with respect to the influence of environmental ‘proximate’ factors.

These contrasts are interpreted primarily in terms of the different evolutionary origins of the two species, although the various constraints on the reproductive cycle, which are imposed by their differing nesting adaptations and feeding behaviour, are also discussed. Models of the reproductive cycle at the individual level, and of the breeding season(s) at the population level, are developed for both species. Using data for some other seabird species breeding in south-western Australia, the Crested Tern and Silver Gull models are incorporated in a general explanation of ‘double-nesting’. The views presented not only provide some insight into a unique, localised phenomenon but should also lead to a re-examination of conventional ideas about seabird breeding seasons generally.

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