Impact of weather on partial loss of nestlings in the Red-backed Shrike Lanius collurio in eastern Poland

Abstract

The influence of ambient temperature and rainfall on the size of partial losses in broods of the Red-backed Shrike was studied in the extensive agricultural landscape of eastern Poland in 1999-2003. Nestlings were divided into two age classes: up to the 5th day after hatching and the 6-10th day of life. The entire period of the nestlings' stay in the nest (1-10th day of life) was also considered. The ambient temperature did not influence the size of losses at either stage of the nestling life. Rainfall affected the size of nestling losses in the periods when they were 6-10 and 1-10 days old. The influence of rainfall explained only 11% of nestling losses. Thus, one should expect some factors other than weather conditions to cause partial losses in Red-backed Shrike broods in the study area, at least in seasons with an average pattern of air temperature and rainfall. Among such factors, the structure of territories variation in food abundance should undoubtedly be considered.