Long-term, not short-term, temperatures predict timing of egg laying in European Starling.

The article investigates how ambient temperature influences the timing of egg laying in European Starlings (Sturnus vulgaris), challenging the common assumption that short-term temperatures immediately before laying are the primary cues. Using 20 years of data and three analytical approaches—including an unconstrained sliding window analysis, a traditional sliding window method, and biologically informed temperature windows—the study finds that long-term temperature windows spanning January to early April, particularly mid-winter temperatures (January 8 to February 22), best predict laying dates. There was no evidence supporting the influence of short-term temperatures within one month before laying or temperatures from the previous August on laying timing. The findings suggest that European Starlings integrate long-term temperature information, possibly indirectly via temperature effects on the development of ectothermic insect prey, to time reproduction, highlighting a need to better understand the physiological and ecological mechanisms underlying this integration.