The importance of arable habitat for farmland birds in grassland landscapes

1. Over the last 25 years, populations of seed-eating birds have declined s everely over most of western Europe. Local extinctions have occurred in gra ssland-dominated areas in western Britain, which may be influenced by loss in habitat diversity and a decline in the amount of arable cultivation. 2. We used the large-scale British Breeding Bird Survey of 1998 to investig ate the importance of arable habitat within grassland landscapes for 11 com mon seed-eating birds and four similar sized insectivores. Generalized line ar models were used to model the number of birds recorded in agricultural h abitat within survey squares as a function of the amount of arable habitat present. 3. Numbers of grey partridge Perdix perdix, skylark Alauda arvensis, tree s parrow Passer montanus', corn Miliaria calandra and reed buntings Emberiza schoeniclus, yellowhammer Emberiza citrinella and whitethroat Sylvia commun is increased with the amount of arable habitat present in a survey square; the numbers of house sparrow Passer domesticus, four finch species., dunnoc k Prunella modularis, robin Erithacus rubecula and blackcap Sylvia atricapi lla did not. 4. The positive association between numbers of some species and arable habi tat within 1-km squares was strongest where arable habitat was rare in the surrounding area, and weakest or even reversed when arable habitat was comm on. These results demonstrate the scale-dependence of bird-habitat associat ions in agricultural landscapes, only demonstrable where data are available at fine grain over large geographical areas. 5. These results support the hypothesis that range contractions (i.e. local extinctions) of some granivorous species have occurred because of contract ion in arable cultivation. The loss of arable habitat where it is scarce ma y be causing declines in some areas, even though intensification of arable management is thought to be the main cause of declines elsewhere. Agri-envi ronment schemes may need to vary between regions, for example to encourage arable cultivation in pastoral areas.