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The Influence of Age and Pair-Bond on the Breeding Biology of the Red-Billed Gull Larus novaehollandiae scopulinus

J. A. Mills
Journal of Animal Ecology
Vol. 42, No. 1 (Feb., 1973), pp. 147-162
DOI: 10.2307/3409
Stable URL: http://www.jstor.org/stable/3409
Page Count: 16
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Influence of Age and Pair-Bond on the Breeding Biology of the Red-Billed Gull Larus novaehollandiae scopulinus
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Abstract

(1) The effects of age and mate changes on the breeding biology of the red-billed gull Larus novaehollandiae scopulinus have been studied for five seasons at the Kaikoura Peninsula, New Zealand. (2) An average of 42% of the birds return to breed at the natal colony, the effect being more pronounced in males than females. (3) The age of first breeding is variable; they are capable of breeding at 2 years but the majority do not do so until they are either 3, 4 or 5 years of age. Males tend to breed when younger than females. (4) There was a marked tendency for gulls, particularly the older ones, to retain the pair-bond of the previous season. Approximately 4% were known to have changed mates because the mate of the previous season had died, but 27% of the gulls changed when their former mate was present on the colony. Those which changed mates had had a significantly lower hatching and fledging success the previous season than did those which retained mates. (5) Gulls breeding for the first time acquired mates of similar age, but females changing mates, frequently paired with younger males. (6) The maturation of the testis and ovary occurred significantly earlier with increasing age of the bird. (7) The age of the female influenced the date of laying, clutch size and post-fledging survival of chicks. The hatching and fledging success of different-aged birds differed significantly, but neither improved with increasing age of females. (8) Females which retained the pair-bond of the previous season bred earlier in the season and laid more eggs than females which changed mates, but did not have increased breeding success. The age of the male also influenced the laying date and clutch size of the female. (9) It is considered, although there are obvious disadvantages in changing mates, in some cases it is an advantage for incompatible pairs to split up. The delayed breeding and smaller clutch sizes resulting after the change of mates are believed to result from the long period of adjustment needed before the pair can function efficiently.

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