Breeding success and survival in the common swift Apus apus: A long-term study on the effects of weather

In an analysis of data collected between 1954 and 1993, the breeding success of swifts Apus apus was found to have been positively related to temperatures in June, especially in recent years. Adult survival until the next breeding season, by contrast, was found to have been more vulnerable to low temperatures in July, at the end of the breeding season. In addition to the effects of changes in June and July temperatures, both breeding success and survival have shown further long-term trends, increasing and then decreasing through the study period. A simulation integrating all these effects suggests that lifetime reproductive success (LRS) is influenced more by changes in lifespan than annual breeding success, and so fluctuations in July temperatures, but not June temperatures, would have important effects.