TERRITORY DISTRIBUTION AND BREEDING SUCCESS OF SKYLARKS ALAUDA-ARVENSIS ON ORGANIC AND INTENSIVE FARMLAND IN SOUTHERN ENGLAND

1, Skylark numbers declined by 51% between 1968 and 1995 on UK lowland farmland; a loss of approximately 3 million breeding birds. This stud y examined whether distribution and breeding success of skylarks varie d with the cropping of organically and intensively managed fields in s outhern England in accordance with the hypothesis that changes in agri cultural land-use and intensity of management have contributed to this decline. 2, Density was lowest on fields surrounded by tall boundary structures or unsuitable habitat, and those with tall, dense vegetatio n cover. After controlling for these effects, set-aside and organicall y-cropped fields supported significantly higher skylark densities thro ughout the breeding season than intensively cropped fields or grazed p asture. Nests were usually built in crops between 20 and 50 cm tall. I n fast-growing broadleaved crops (e.g. oilseed rape, legumes), skylark s held territories, but no nesting activity was observed. Rapid crop g rowth probably allows too little time for nesting to begin. 3. Breedin g success was higher on set-aside than on intensively managed cereals. Predation caused most nest failures, but did not vary in frequency wi th crop type. Silage cutting and trampling caused many failures on gra ss fields, and all cases of apparent brood starvation occurred in cere al fields. These breeding success data, together with published estima tes of survival rates, suggest that skylark pairs must make 2-3 nestin g attempts per season in order for populations to be self-sustaining. A single crop type rarely provides a suitable vegetation structure for nesting throughout the breeding season. Skylarks therefore require st ructurally diverse crop mosaics in order to make multiple nesting atte mpts without territory enlargement or abandonment. Mixed farms are mor e likely to fulfil these requirements than those dominated by winter c ereals and broad-leaved crops. 4, These results are consistent with th e hypothesis that loss of mixed farming and rotational cropping, and c oncomitant increases in autumn sowing of crops, agrochemical inputs, m ultiple silage cuts and grazing intensities since the 1950s have reduc ed the breeding productivity and population density of skylarks on low land farmland in southern England. 5, The following recommendations ar e made for changes in farming systems that would assist the conservati on of breeding skylark populations on lowland farmland. Organic farmin g systems, set-aside and habitat management for gamebirds are all like ly to improve nesting and feeding conditions for skylarks, More genera lly, breeding skylark populations are only likely to increase on farms that reduce agrochemical inputs, reduce grazing intensity and frequen cy of silage cutting, and increase the structural diversity of field v egetation by adopting mixed rotations of winter and spring cereals, ro ot crops and grass. Traditional mixed farming systems of this kind are now rarely economically desirable. Only agricultural policy reforms m otivated in part by environmental concerns rather than solely by produ ction control are likely to direct subsidy support to reduced-intensit y, mixed farming enterprises of this kind, and thus help to restore po pulations of breeding skylarks on lowland farmland.