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The Biological Significance of Age-Specific Return Schedules in Breeding Purple Martins
Eugene S. Morton and Kim C. Derrickson
Vol. 92, No. 4 (Nov., 1990), pp. 1040-1050
Published by: Cooper Ornithological Society
Stable URL: http://www.jstor.org/stable/1368740
Page Count: 11
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We describe age-related differences in return dates in the colonial Purple Martin (Progne subis). Adults ≥4 years of age returned earlier than Age 3 adults which returned earlier than first-time breeders. Males tended to return slightly earlier than females in birds Age 3 and older. The arrival schedule results from competitive asymmetries over secondary cavity nest sites and predation pressure but not from the timing of reproduction. Older and earlier returning birds select higher nests. Nests located in higher levels suffer significantly less predation from climbing predators. The return dates of mates are not correlated but mated pairs do tend to be similar in age. Egg-laying date is not related to arrival date. Greatly reduced certainty of paternity is correlated with a reduction in reproductive effort in first-time breeding males. The variable subadult plumage in Age 2 males provides for individual recognition, which benefits them in within age-class nest-site competition.
The Condor © 1990 Cooper Ornithological Society