Synchrony of woodland bird populations: the effect of landscape structure

Abstract

The influence of environmental stochasticity and dispersal in producing patterns in population synchrony was examined for 53 woods censused annually from 1990 to 1999 for nine resident bird species (wren Troglodytes troglodytes, dunnock Prunella modularis, robin Erithacus rubecula, blackbird Turdus merula, song thrush Turdus philomelos, long‐tailed tit Aegithalos caudatus, blue tit Parus caeruleus, great tit Parus major, and chaffinch Fringilla coelebs) and four migrant bird species (garden warbler Sylvia borin, blackcap Sylvia atricapilla, chiffchaff Phylloscopus collybita and willow warbler Phylloscopus trochilus). Twelve species showed global synchrony of population counts due to regional population trends and widespread annual population fluctuations. There was a clear link between population fluctuations and winter weather for wren, and three other species showed their largest population declines after the coldest winters. Eight species showed a decline in synchrony with distance between woods, and there was evidence for dispersal causing this pattern in three species. Landscape structure affected patterns of synchrony in several species, with lower synchrony in landscapes with less woodland. For three species, this difference in synchrony across a landscape gradient of decreasing woodland cover accounted for the decline in synchrony over distance. Three species showed greater synchrony between woods with similar amounts of hedgerow in the surrounding landscape, suggesting that the surroundings of a wood influence the population dynamics of some species breeding in the wood. Habitat fragmentation can alter the processes contributing to population synchrony. Loss of woodland reduces the relative abundance of woodland bird species. The remaining patches of habitat are smaller, more isolated and are set in a more hostile landscape, all of which may disrupt dispersal between patches and alter the population dynamics within woods.