Weather effects on nestling survival of great tits vary according to the developmental stage

Abstract

Organisms change breeding investments as a function of the environment, thereby maximizing reproductive success. Climate change studies of avian life‐history have long focused on plasticity of laying dates and clutch sizes in response to weather conditions prior to clutch initiation. By contrast, effects of unpredictable weather events occurring after initial reproductive decisions are made have largely been ignored, despite becoming increasingly important with ongoing climate change. We studied the detrimental effects of fluctuations in temperature and precipitation during various nesting phases of great titsParus major, identifying the developmental age windows where weather fluctuations affected hatching, nestling mass and fledging success. We used a longitudinal (8‐year) dataset of great tits breeding in nest boxes in southern Germany and applied a recently introduced explorative approach that does not require a priori assumptions on the time windows (range of ages) over which weather may affect reproductive parameters. Lower temperatures and higher precipitation during the nestling phase negatively affected nestling mass and survival: nestlings between the ages 6 and 9 days were most susceptible to this form of variation in weather. Effects of weather did not differ between years, i.e. there was no evidence for ‘good' versus ‘bad' years. Future research should focus on the mechanisms underpinning effects of weather on nestling growth and survival in other populations and consider if age‐dependent weather consequences occur in a wide variety of taxa, as specific developmental stages may serve as weak spots in a scenario of increasing recurrence of weather extremes.