Nest predation rates and nest detectability in different stages of breeding in Blackbirds Turdus merula

Nest predation in relation to nestling noise and nest conspicuousness was investigated in Blackbirds. In one year there was no temporal variation in nest predation or significant variation in nest predation rates due to nest conspicuousness. In a second year nest predation rates were significantly higher in the early stages of breeding (laying and the first half of incubation), and nests that were less conspicuous were more likely to survive longer or succeed. In both years there was no significant difference in nest predation rate between the second half of incubation and the first half of the chick stage, but there was a significant decrease in nest predation rate between the first and second half of the chick stage. The results suggest that increased noise from nests during the chick stage did not increase the probability of nest predation, and that if nest predation is important in determining clutch size in Blackbirds, selection may occur early on in breeding.