Effects of forest fragmentation on avian breeding activity.

Ecosystem decay is responsible for biodiversity declines following forest fragmentation, as initially abundant species may become rare, or experience delayed local extinctions. However, the underlying mechanisms behind the delayed local extinction of certain species following fragmentation are unknown. Species declines may be attributed to an inadequate number of breeding adults required to replace the population or decreased juvenile survival rate due to reduced recruitment or increased nest predation pressures. This study uses 10 years of avian banding data, five years before and four years after fragment isolation, at the Biological Dynamics of Forest Fragments Project near Manaus, Brazil, to investigate the breeding activity hypothesis which predicts that there is less breeding activity and fewer young after relative to before fragment isolation. We found support for the breeding activity hypothesis in both insectivorous and frugivorous birds (effect sizes 0.45 and 0.53, respectively), and in birds with open cup, and enclosed nesting strategies (effect sizes 0.56 and 0.44, respectively) such that on average there were more breeding birds in fragments before isolation relative to after fragment isolation. In addition, a larger proportion of birds in the community were actively breeding before fragment isolation relative to after fragment isolation. Unexpectedly, there was no significant decrease in the number of young birds after fragment isolation, although sample sizes for young were very small, potentially from sustained immigration of young birds to fragments after isolation. Together, these results provide some of the strongest evidence to date that avian breeding activity decreases in response to fragment isolation, which could be a fundamental mechanism that leads to ecosystem decay. This article is protected by copyright. All rights reserved.