The effect of weather conditions on the breeding biology of the Eurasian Bittern Botaurus stellaris in eastern Poland

Abstract

Numerous studies carried out on different bird species have shown that weather conditions can modify their breeding biology at various stages in their reproduction. Directly or indirectly, meteorological factors can affect breeding success by modifying brood survival and the availability of food resources. The present study examined the relationships between weather conditions and selected breeding parameters in the Eurasian Bittern. It was carried out in 2003–2009 on extensively farmed carp ponds located in eastern Poland. With the aid of multiple regression models, we analysed the effect of the mean ambient temperature, mean daily temperature range, mean daily minimum temperature, total precipitation and mean wind speed on the number of eggs in a clutch, egg size, and partial losses of eggs and chicks. A significant adverse relationship between the sum of rainfall in the laying period and the mean egg volume in a clutch was found. Greater mortality among young Eurasian Bitterns was also correlated with strong rains and winds during the chick-rearing period. There were two critical periods in the population we studied – before the first egg was laid, and the chick-rearing period – which were particularly sensitive to changes in the weather.