Influence of temperatures during the nestling period on post‐fledging survival of great tit Parus major in a Mediterranean habitat

Survival during the first year is one of the most important factors determining fitness in birds. Birds have poor thermoregulatory abilities during the nestling period when the plumage is not fully developed, thus temperature during the nestling period is a serious candidate to affect post‐fledging survival, although it has been usually ignored in previous studies. We analysed the relationship between temperatures and post‐fledging survival in a great tit Parus major population in Sagunto (Spain) using capture‐recapture data from 12 years. Hatching dates, mass at fledging and temperatures during the nestling period (maximum, minimum and mean ambient temperatures as an estimation of the mean and extreme weather conditions that chicks encountered at the nest) were used as individual covariates. Mean post‐fledging survival was 0.13±0.01. Adult survival probability was 0.64±0.02. Multi‐model inference suggested that post‐fledging survival increased with fledging mass, and decreased as temperatures increased. Furthermore, the effect of mass on survival was less important as temperature was higher. We consider that high temperatures affect nestlings’ health due to low thermoregulatory abilities of nestlings. Model selection did not support a relationship between hatching dates and survival once mass and temperatures were taken into account. The results suggest the possibility that the effect of date on post‐fledging survival found in previous studies was, at least in part, a consequence of the seasonal pattern of temperature variation.