Fluctuating asymmetry increases with habitat disturbance in seven bird species of a fragmented afrotropical forest

Abstract

We studied fluctuating asymmetry (FA) in the tarsus length of seven forest-restricted bird species, two of which are globally critically endangered, in three indigenous forest remnants of a recently fragmented, afrotropical biodiversity hot spot. Based on mixed regression analysis and an extension of Levene's test, individuals from the most degraded fragment showed four- to sevenfold higher asymmetry levels compared to those from the least degraded one, with intermediate levels in the moderately disturbed fragment. When comparing contemporary FA levels with measurements of museum specimens collected 50 years ago, we found highly significant increases in asymmetry in the most degraded fragment but no differences in the least degraded one. These strikingly parallel spatial and temporal patterns across species confirm that repeated measurements of FA can provide a sensitive early warning system for monitoring stress effects in highly threatened ecosystems.