Survival of suburban blackbirds Turdus merula varies seasonally but not by sex

Survival is a key demographic parameter in bird populations yet remarkably little is known about the seasonal pattern of survival. Mortality may increase as a result of breeding behaviour, harsh environmental conditions, resource limitation or any combination of these; knowing which is important for understanding the ecology of population change. We analyse an intensive ten-year colour marking programme of European blackbirds Turdus merula to estimate seasonal and sex-specific survival rates. The annual survival rate (0.67) was similar to that produced from analyses of dead recoveries across Britain, but within year variation was significant. Survival rates were lowest during the early part of the breeding period and highest in the autumn, but there was little difference between the sexes. Understanding this pattern of variation is important in interpreting both life-history variation and the mechanisms of population change.