Effects Of Temperature Variability On Egg Mass And Clutch Size In Great Tits

Models of climate change generally predict rising mean global temperatures combined with greater variability in some regions. While relationships between mean temperature and several reproductive parameters are well documented, the effect of day-to-day variation in ambient temperature has received little attention. In our study, temperature variation had no significant effects on clutch size in a wild population of Great Tits (Parus major). In contrast, egg mass tended to be smaller when ambient temperatures during the week prior to laying were more variable. We suggest that variable temperatures may be disadvantageous to an egg-laying bird. Thermal variability should therefore be considered as a discrete factor, distinct from mean temperature, when assessing the consequences of climate changes for breeding birds.