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Why do female migratory birds arrive later than males?
Article first published online: 5 SEP 2006
DOI: 10.1111/j.1365-2656.2006.01151.x
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How to Cite
KOKKO, H., GUNNARSSON, T. G., MORRELL, L. J. and GILL, J. A. (2006), Why do female migratory birds arrive later than males?. Journal of Animal Ecology, 75: 1293–1303. doi: 10.1111/j.1365-2656.2006.01151.x
Publication History
- Issue published online: 26 SEP 2006
- Article first published online: 5 SEP 2006
- Received 8 March 2006; accepted 6 July 2006
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Keywords:
- arrival timing;
- extra-pair fertilization;
- population sex ratio;
- sex-role reversal;
- territoriality
Summary
- 1In migratory birds males tend to arrive first on breeding grounds, except in sex-role reversed species. The two most common explanations are the rank advantage hypothesis, in which male–male competition for breeding sites drives stronger selection for early arrival in males than females, and the mate opportunity hypothesis, which relies on sexual selection, as early arrival improves prospects of mate acquisition more for males than for females.
- 2To date, theoretical work has focused on selection for early arrival within a single sex, usually male. However, if fitness depends on territory quality, selection for early arrival should operate on both sexes. Here we use two independent modelling approaches to explore the evolution of protandry (male-first arrival) and protogyny (female-first arrival) under the rank advantage and mate opportunity hypotheses.
- 3The rank advantage hypothesis, when operating alone, fails to produce consistent patterns of protandry, despite our assumption that males must occupy territories before females. This is because an individual of either sex benefits if it out-competes same-sex competitors. Rather than promoting protandry, the rank advantage mechanism can sometimes result in protogyny. Female–female competition is stronger than male–male competition early in the season, if females compete for a resource (territories occupied by males) that is initially less common than the resource of interest to males (unoccupied territories).
- 4Our results support the mate opportunity hypothesis as an explanation of why protandry is the norm in migratory systems. Male-biased adult sex ratios and high levels of sperm competition (modelled as extra-pair young: EPY) both produce protandry as a result of sexual selection. Protogyny is only observed in our models with female-biased sex ratios and low EPY production.
- 5We also show that the effects of sex ratio biases are much stronger than those of EPY production, explore the evidence for sex ratio biases and extra-pair paternity in migratory species and suggest future research directions.