Selective mortality of waders during severe weather

Capsule The birds that died were generally smaller. Aims To look for selective mortality of waders in severe weather. Methods Biometric measurements of birds found dead in a local severe weather event in February 1991 on The Wash Estuary, UK, were compared with measurements of the same species caught alive in February in previous and following years. Results Eight of 13 intraspecific biometric comparisons between birds found dead and those captured in February in previous years were significantly different. Of these comparisons seven showed that the birds that died were smaller. Three of nine intraspecific biometric comparisons between birds dying during the severe weather and those caught in subsequent years were significant; of these comparisons the dead birds were smaller in two cases. Of eight comparisons between the biometrics of live birds before and after the severe weather event, only one was significant: the bill lengths of Eurasian Oystercatchers Hoematopus ostralegus were longer after the event. Conclusions The birds that died due to the severe weather incident do not appear to be a random sample of the populations present. Smaller birds died disproportionately. However, in comparisons of birds captured before and after the severe weather event only Oystercatcher's bill lengths increased significantly and it is unlikely that this was related to the severe weather. Thus, the size-biased mortality did not result in long-term changes in the size distributions of the species affected.