DEVELOPMENTAL STABILITY AND IDEAL DESPOTIC DISTRIBUTION OF BLACKBIRDSIN A PATCHY ENVIRONMENT

Previous studies of the distribution of breeding blackbirds Turdus mer ula in a patchy environment of tree lots in a matrix of farmland have shown that nestling mortality due to nest predation and starvation dec reased with increasing habitat patch size. The net annual reproductive success increased with increasing patch size and accordingly a larger fraction of yearling blackbirds appeared to be forced to settle in sm all habitat patches. In this study I independently assess habitat qual ity as perceived by the blackbirds using a measure of developmental st ability as a criterion. Fluctuating asymmetry in wing length and tail length of blackbird nestlings and fledglings decreased with increasing patch size. Nestlings with high levels of asymmetry also had high lev els of asymmetry as independent fledglings, and local post-fledging su rvival probability was inversely related to the level of fluctuating a symmetry. Adult blackbirds breeding in small habitat patches did not h ave higher asymmetry than those breeding in large patches, and this ob servation suggests that natural selection had reduced the level of asy mmetry among adults. Developmental stability is concluded to be a pote ntially useful independent measure of performance in studies of conser vation biology and landscape ecology.