The effects of ambient temperature and rainfall on the clutch initiation, egg mass and clutch size in the European starling ( Sturnus vulgaris)

Abstract

Climate change is an ongoing global phenomenon resulting in elevated temperatures and more intense rainfall events. These changes in temperature and rainfall have affected the breeding behaviour of many avian species. The purpose of this study is to examine the effects of ambient temperature and rainfall on clutch initiation date, egg mass, and clutch size in European starlings (Sturnus vulgaris). I predicted that starlings would initiate clutches earlier with increases in temperature and rainfall. I also predicted that increases in temperature and rainfall would result in higher egg mass and clutch sizes. A free-living colony was studied from 2007-2009 and 2011-2014 for clutch initiation date and clutch size (n = 191 clutches), while egg mass was determined in 2013 and 2014 (n = 76 clutches). There was no effect of mean ambient temperature or mean rainfall on clutch initiation in the European starling over the seven years of data. There was no significant difference between egg mass and mean ambient temperature or mean rainfall; however, first-laid eggs were significantly heavier than last-laid eggs. Contrary to my prediction, clutch size decreased with increases in temperature and showed no correlation with rainfall. The negative correlation between clutch size and ambient temperature is evidence of a seasonal decline, a common phenomenon in birds. This is likely due to a decrease in female condition over the breeding season. It is likely that the breeding behaviour of starlings is controlled by a variety of external and internal cues.