No evidence of weather effect found on the clutch size, eggs sizes and their hatchability in the red-backed shrike Lanius collurio in eastern Poland

摘要

Weather conditions can influence birds' breeding performance through changes in metabolism of a female and can also directly affect eggs and chicks. I studied the influence of ambient temperature, variation in ambient temperature and rainfall on the breeding performance of the red-backed shrike Lanius collurio in 1999-2003 in the extensively agricultural landscape of eastern Poland. I did not find any influence of the analysed weather conditions on clutch size, mean egg volume in a clutch, variation of egg volume in a clutch and losses between the numbers of laid and hatched eggs. A probable explanation is that weather and food conditions are usually favourable for red-backed shrikes during egg laying and incubation, and males provide frequent supplemental feeding to the females at these stages of breeding. Probably, the extensively farmed agricultural area provides an abundant food base for the study population living there, which allows the red-backed shrike to quickly compensate its energy expenditures.