Migrants in Neotropical bird communities: an assessment of the breeding currency hypothesis

1. Explanations for the integration of migratory and non-migratory (resident) birds in the Neotropics have been complicated by the paradox that arthropod abundances are low when bird abundances reach their annual peak. The breeding currency hypothesis offers an explanation for this paradox by postulating that resident birds are limited in the breeding season by the availability of large arthropods suitable for reproduction, whereas the carrying capacity of all birds in the non-breeding season is limited by the availability of arthropods suitable for self-maintenance of adults. 2. Field data from Jamaica supported this hypothesis. Among 19 sites, the ratio of migrant to resident bird abundance was correlated negatively with the ratio of large arthropod biomass in the breeding season to total arthropod biomass in the non-breeding season. 3. However, after controlling for effects of arthropod seasonality, migrant to resident bird abundance ratios were higher in human-disturbed than undisturbed sites. 4. Other factors may interact with the availability of food for nestlings to limit the populations of resident birds below carrying capacities set by non-breeding season arthropod abundance, thereby creating a set of resources available to non-breeding migrants.