Effects of a drought episode on the reproductive success of European free-tailed bats (Tadarida teniotis)

Increases in the frequency and severity of droughts are expected in the Mediterranean region under ongoing climatic change, but their potential effects on bat populations still remain largely unstudied. Here we address this issue, by using data from a monitoring program of Tadarida teniotis to assess the reproductive consequences of a severe drought event. Unusually dry conditions occurred in the first of the 2 years under study (2012–2013), when the annual precipitation was the lowest on record during three decades, and the normalized difference vegetation index (NDVI) was well below the long term median, particularly during the pre-breeding season. A total of 1304 individuals were captured between May–October 2012 and 2013, and their body condition index (BCI), gender, age, and reproductive status were assessed. In both years, the BCI of adults increased throughout the year, reaching its maximum in October. BCI in May was significantly lower in 2012 than 2013, but converged thereafter to similar values. The sex-ratio varied throughout the year, but the proportion of females was consistently higher in both years. The number of pregnant or lactating females and the proportion of juveniles were significantly lower in 2012 than in 2013. Overall, our results suggest that the drought event largely impaired the reproduction of T. teniotis, though it only affected body condition early in the pre-breeding season. Possibly, dry conditions in 2012 resulted in reduced food resources during pre-breeding, limiting individuals’ ability to restore their body condition after the winter and before breeding season. As a consequence, most individuals did not produce offspring, probably using the food resources available during the dry breeding season to restore body condition before winter. This is in line with the view that long-lived species reduce investment in reproduction to maximize adult survival during stressful periods, and suggest that multiyear droughts may result in population declines due to recurrent reproductive failure.