Factors affecting fledglings survival in urban population of European blackbirds in Szczecin (NW Poland).

The first-year survival alters population growth rates and viability in birds, however this period remains the least-studied of the avian life stages. Here we present results of the 19 years of study of fledglings apparent survival of urban population of European blackbird Turdus merula in Szczecin (NW Poland). We checked for possible influence on survival of several factors, including parental traits, such as parental age, their previous breeding experience, natal brood size, presence of another brood in a given breeding season and the time gap between clutches of a particular pair. Moreover, we incorporate into our analysis fledging's hierarchy in the brood, its fledging time in the breeding season, temperature and precipitation during the first months of life. We also investigated changes in the apparent survival over 19 years. We found that the individual's hierarchy in the nest, and the day of fledging had the strongest influence on the apparent survival, with heavier birds fledged earlier in the season surviving better. Increase in parental age and previous breeding experience of the pair could result in enhanced survival. Surprisingly increased precipitation lowered fledglings' survival. During the 19 years of the study fledglings' apparent survival dropped about 10%.