We examined breeding performance and the nest survival of Booted Warbler Iduna caligata on abandoned fields in Vologda region, Russia. We modelled daily survival rates (DSR) using data on 250 nests found in 2002-2011. We compared relative effects of year, nest age, date, weather conditions and nest placement characteristics. Clutch size did not vary over the study period and was on average 5.69 ± 0.04 eggs. Inter-seasonal variability was the most important component of DSR variation. The top model included a year effect, a quadratic nest age term and an interaction between year and quadratic age. Overall nest success varied greatly from 0.03 in 2008 to 0.7 in 2007. Nest height was an important nest placement covariate, nest remoteness from villages and roads were not influential. We detected the species composition of predators by watching nests of Booted Warblers and other grassland passerines as well as by observing the artificial nests. The main predators were carnivorous mammals, Common Viper Vipera berus, Harriers and corvids. Predator pressure was the main factor that determined nest success of Booted Warblers. Intra- and inter-annual fluctuations in the activity of predators may cause corresponding changes in nest success of Booted Warbler.
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