Effects of forest fragmentation on the weight of understory birds at the Biological Dynamics of Forest Fragments Project in Amazonia

Deforestation and habitat fragmentation are known as the chief drivers of biodiversity loss. Less is known about the condition of species and individuals that remain in disturbed habitats. Theory predicts that resources are more limited after compared with before fragment isolation. Thus, we assessed how body condition of individual birds' changes in response to forest fragment isolation. We compared weights of the same individually banded birds caught in mist nets within 5 years before and after fragment isolation and assessed the population-level changes of three species at the Biological Dynamics of Forest Fragments Project in the Brazilian Amazon. We predicted that fragment isolation would result in reduced weight for all bird species. Out of the 3466 bird mist net captures before and after isolation in the 1980s and the 2150 birds captured before and after re-isolation of fragments in the 2010s, only 73 adult individuals from 36 different species were recaptured, suggesting that few individuals stay in fragments. Contrary to predictions, insectivorous species that remained in fragments gained weight (3.43%) after fragment isolation while frugivorous birds maintained a stable weight. While recent studies report long-term declines in body mass of birds in tropical unfragmented tropical forests, our results provide a novel analysis into how avian body mass responds to habitat fragmentation. Further studies on the body condition of individuals that remain in fragments and the ultimate consequences of fluctuations in body condition are needed to better understand why some individuals and species are more susceptible to forest fragmentation than others. Abstract in Portuguese is available with online material