High fluctuating asymmetry in birds in a large neotropical city

Urbanisation is a powerful environmental force, negatively impacting the few organisms that persist in urban areas. Fluctuating asymmetry (FA), a recognised bioindicator of ontogenetic and environmental stress, may reflect such impacts, though its role in assessing urban intensification remains unclear. We investigated the relationship between urbanisation intensity and FA in birds, analysing 10 locally abundant species in Brasília city, Brazil. Our hypothesis posited that birds in more urbanised areas would exhibit higher FA. We measured bird tarsus and wing to assess asymmetry and also examined whether FA differed between traits. Neither wing nor tarsus FA increased with urban intensity. However, tarsus FA was consistently higher than wing FA. Notably, our FA values for both traits are comparable to, or in the case of tarsus, exceed those reported for birds in fragmented forests. These findings suggest that urbanisation (even at lower intensities) may impose stronger genetic and/or environmental stress on developmental stability than previously recognised.