Natural selection on tail and bill morphology in Barn Swallows Hirundo rustica during severe weather

Authors:
Publisher website
Google Scholar
Abstract
An unusual six‐day period of cold, rainy weather caused mortality among Barn SwallowsHirundo rusticain southwestern Nebraska, USA, in May 1996. We compared birds that died during the cold to those still alive when the severe weather ended. Among males, survivors had significantly longer culmens and significantly less variance in outer‐tail asymmetry than non‐survivors. Among females, survivors had significantly longer outer tails and significantly less variance in outer‐tail length, overall body size and outer‐tail asymmetry than non‐survivors. Larger birds in general and those with less asymmetry in wing and outer tail tended to be favoured during this weather event. Long tails may reflect condition in females and, along with high levels of symmetry in wing and outer tail, improve foraging efficiency during extreme conditions. Males with long tails did not appear to suffer survival costs. Larger size probably allows more fat to be stored and may confer thermal benefits to swallows during late spring cold snaps. Similar mortality events have apparently occurred in the study area on only one other occasion since 1875.

This publication has 44 references indexed in Scilit: