Bet-hedging and the orientation of juvenile passerines in fall migration
Article first published online: 30 JUN 2009
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
Journal of Animal Ecology
Volume 78, Issue 5, pages 990–1001, September 2009
How to Cite
Reilly, J. R. and Reilly, R. J. (2009), Bet-hedging and the orientation of juvenile passerines in fall migration. Journal of Animal Ecology, 78: 990–1001. doi: 10.1111/j.1365-2656.2009.01576.x
- Issue published online: 29 JUL 2009
- Article first published online: 30 JUN 2009
- Received 6 March 2009; accepted 15 May 2009 Handling Editor: Jane Reid
- coastal effect;
- Dendroica caerulescens;
- vector navigation;
- within-clutch variation
1. Bet-hedging of innate migratory orientation of juvenile passerines may be a fitness-enhancing strategy for fall migration. Experimental studies support the view that juvenile passerines on their first migration to unknown winter grounds orient on a predetermined vector programme and make little or no adjustment for wind displacement. This trait, coupled with the unpredictable profile of wind speed and direction that the juvenile will encounter during migration, suggests that the fitness of a parent’s juvenile offspring will be highly variable from year to year. Under these circumstances, within-clutch phenotypic variation in migratory orientation may be evolutionarily favoured.
2. To explore this hypothesis, a migration model is developed for a small passerine with breeding grounds in New England and winter grounds in the Caribbean. Parameterization is based on life history data of the neotropical migrant Dendroica caerulescens, the black-throated blue warbler. The model is simulated for the offspring of 20 000 adult females under each of a wide range of potential orientation programmes, incorporating stochastic wind profiles along potential migratory routes, based on 7 years of wind data for eastern North America.
3. Under these simulations, bet-hedging in the form of within-clutch variation of migratory orientation strongly dominates within-clutch homogeneity, yielding higher geometric mean fitness in all vector programmes considered.
4. The simulation results provide a potential explanation for the variation observed in the tracks of juvenile passerines. Bet-hedging also explains the extensively-documented ‘coastal effect’ in which fall banding stations along the Atlantic coast of the United States consistently capture a much higher percentage of juvenile birds than do more inland stations.
5. Bet-hedging is consistent with the published finding that slower flying birds exhibit greater variation in their migratory orientation than faster flying birds.
6. The bet-hedging model of migratory orientation presented in this paper provides a theoretical structure capable of organizing a diverse collection of field and laboratory observations as predictable consequences of an evolutionarily favoured strategy. This theory may constitute a major advance in our understanding of bird migration and thus justifies the design and execution of new laboratory and field experiments to assess its power and predictive reach.