The demography of blackbirds Turdus merula in rural habitats: is farmland a sub-optimal habitat?
Abstract
A population of 54-76 pairs of Turdus merula was studied on 350 ha of lowland farmland (arable, grazed and leys), 90 ha of broadleaved woodland (dominated by Quercus robur and Acer pseudoplatanus, with sparse understorey and patches of bramble (Rubus fruticosus) and thorn (Prunus spinosa)), and in woodland/farmland boundaries at Wytham, Oxfordshire, England. Woodland was occupied by the birds at a higher density than farmland, but within the woodland there were patches of low and high density occupation, and non-occupation. Habitat and territory type did not affect survival, breeding or clutch size, although farmland females laid smaller eggs. There were more young males in farmland than woodland, and in sparsely occupied territories, but no differences in female populations across habitats. Reproductive success was low across all habitats, but tended to be more successful in densely occupied habitats. The results indicate that farmland blackbirds show some of the characteristics of populations in sub-optimal habitats.