Factors affecting breeding performance in merlins (Falco columbarius) : tactics, roles and responses of two sexes
Espie, Richard Henry Maclaren
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Among females, age related improvements in breeding performance were due to the selection of superior breeders. For males, improvements occurred mostly within individuals early in life suggesting that they gained in experience. Past midlife, both sexes with reduced brood size survived better whereas just the opposite was true before midlife. For yearling females, bigger birds were better performers and survived to breed again. Among yearling males, smaller birds had larger broods, but, larger males survived. In adults, body size had little influence on breeding performance in either sex; however, the trends between body size and brood size in the sexes were different. Mate choice of male body size by females was repeatable. However, choice of male size was not related to female size. There was no repeatability of choice for body condition in Merlins. Body size showed high heritability between parents and male offspring, whereas, body condition exhibited low heritability. Territory quality did not affect breeding performance in females. Females in poorer body condition had earlier chick hatch dates and higher LRS than ones in better condition. Hatch date was repeatable for the same females occupying different nest places, but, not so for the same nest places occupied by different females. Among males, surviving birds occupied higher quality territories. LRS was positively correlated with territory quality in males, but, this was due to the influence of the poorest quality territories. When males switched territories they also moved to ones of higher quality. Male body condition was not related to breeding performance nor survival. Hatch date was not repeatable for the same males occupying different nest places. In conclusion, considerable differences exist between the sexes in terms of how the factors studied impact breeding performance. This study illustrates that despite heavy contributions by both sexes to the breeding attempt, their different responsibilities during breeding strongly influences the effect of the factors studied.