Long-term decline in Common Swift Apus apus annual breeding success may be related to weather conditions

Abstract

We analyzed the effect of average monthly temperatures and precipitations (May-July) and of the North Atlantic Oscillation (NAO) on the breeding success of the Common Swift (Apus apus) in Třeboň (South Bohemia) from 1980-1997. Breeding success consistently declined during the observation period. We found that precipitations in May and temperatures in June were positively, and the previous year's May NAO was negatively associated with the percentage of nests that failed to produce any offspring. We found opposite associations between these climatic factors and the average production in nests that did produce offspring. Our results thus suggest that climate (change) may have negatively affected the output of the breeding population. Some of our associations between breeding performance and climate contradict previous observations. Hence, the association between climatic conditions and breeding success in Swift remains not fully explored, and additional long-term studies are needed to clarify the effects of abiotic factors on swift reproduction.