Extensive pastoral farming and marginal land are important for many bird species of conservation concern. This study identified the bird species associated with a range of marginal upland habitats in the Llyn peninsula in Wales and discusses the impact on these species of further land-use change. Bird and habitat surveys of 45 sites were conducted between May and July 2000. The bird species observed at each site were recorded along with the densities of eight species characteristic of marginal farmland. Sites were assigned to land management categories representing different management intensity and land-use options. A binary similarity index was used to quantify species associations with each of these categories and canonical correspondence analysis (CCA) was used to identify associations with individual habitat characteristics. Habitat differences were largely attributable to differences in management. Very few species were recorded on intensively managed sites, although house martin Delichon urbica and swallow Hirundo rustica were significantly associated with improved grassland with scrub or bracken. Sites that were abandoned or under-managed had a high tree density, high cover of bracken Pteridium aquilinium and supported many common scrub or woodland species. Extensively managed sites with unimproved grassland, shrub heath, bracken and scrub (ffridd) were found to be important for several species, including chough Pyrrhocorax pyrrhocorax, wheatear Oenanthe oenanthe, mistle thrush Turdus viscivorus, stonechat Saxicola toquata and meadow pipit Anthus pratensis. High densities of yellowhammer Emberiza citrinella and linnet Carduelis cannabina occurred on sites with improved grassland and gorse Ulex europaeus. This study highlights the need for a diversity of habitats on marginal farmland, which is most likely to be achieved through the distribution of funds to marginal areas through agri-environment and rural development measures.