Abstract
Forest fragmentation may negatively affect populations typically found within continuous forest tracts. Some effects, such as absence from small fragments, are obvious, but other effects may be subtle and easily overlooked. We evaluated the hypothesis that forest birds dwelling in fragments, where microclimatic conditions have been shown to be hotter and drier than in continuous forest, may be in poorer physiological condition than those in the forest interior. We studied two bird species, the Wedge‐billed Woodcreeper ( Glyphorynchus spirurus ) and the White‐crowned Manakin ( Pipra pipra ), common to the fragmented landscape north of Manaus, Brazil. We analyzed feather growth rates in Pipra and Glyphorynchus captured in 1‐, 10‐, and 100‐ha forest fragments and continuous forest. Mean daily feather growth rates of the outer right rectrix of birds captured in fragments were significantly slower than feather growth rates of birds captured in continuous forest. Based on recapture data, Wedge‐billed Woodcreepers probably grew their feathers in sites where they were first captured. White‐crowned Manakins, however, were highly mobile and were recaptured rarely. Although we cannot conclusively show that fragmentation caused birds to be in poorer physiological condition, the data indicate that birds in poorer physiological condition were more likely to be captured in fragments than in continuous forest. Thus, our data suggest that forest fragmentation may have subtle but important effects on species that are relatively common after landscape alteration.