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Determinants of partial bird migration in the Amazon Basin
Article first published online: 10 JUN 2010
DOI: 10.1111/j.1365-2656.2010.01713.x
© 2010 The Authors. Journal compilation © 2010 British Ecological Society
Additional Information
How to Cite
Jahn, A. E., Levey, D. J., Hostetler, J. A. and Mamani, A. M. (2010), Determinants of partial bird migration in the Amazon Basin. Journal of Animal Ecology, 79: 983–992. doi: 10.1111/j.1365-2656.2010.01713.x
Publication History
- Issue published online: 5 AUG 2010
- Article first published online: 10 JUN 2010
- Received 6 November 2009; accepted 11 May 2010 Handling Editor: Mike Boots
- Abstract
- Article
- References
- Cited By
Keywords:
- Bolivia;
- cerrado;
- flycatcher;
- seasonality;
- Tyrannidae
Summary
1. Little is known about mechanisms that drive migration of birds at tropical latitudes. Because most migratory bird species in South America have populations that are present year-round, partial migration (in which only some individuals of a given population migrate at the end of the breeding season) is likely to be common, providing an opportunity to assess proximate mechanisms of migration.
2. Two non-mutually exclusive hypotheses explaining intraspecific variation in migratory behaviour were tested in a Tropical Kingbird Tyrannus melancholicus population in the southern Amazon Basin, where a dramatic dry season decrease in the abundance of insect food for kingbirds may promote migration of some individuals.
3. The Dominance hypothesis predicts sub-dominant individuals migrate at the end of the breeding season and dominant individuals do not, whereas the Body Size hypothesis predicts smaller individuals migrate and larger individuals do not.
4. Based on 4 years of data on individually-marked birds, strong support was found for occurrence of partial migration in the study population.
5. In the best model, the largest males (which are typically older and dominant to younger individuals) had the highest probability of migrating. Younger females (which are the smallest individuals in the population) were also more likely to migrate than other kingbirds, except the largest males. Thus, an individual’s probability of migrating was associated with a more complex interaction of size, age and sex than predicted by current hypotheses.
6. These results suggest that determinants of migratory behaviour differ between North temperate and tropical latitudes. Most tests of partial migration theory have been conducted on granivores (e.g. emberizids) or omnivores (e.g. turdids and icterids) at North temperate latitudes, where seasonality is primarily defined by temperature cycles. In tropical South America, however, the most common long-distance migrants are primarily insectivorous (i.e. tyrannids), and seasonality is largely defined by rainfall cycles.
7. We propose a hypothesis based on seasonal food limitation to explain partial migration of primarily insectivorous species in seasonal tropical habitats.