MAGPIE PICA-PICA AND SONGBIRD POPULATIONS - RETROSPECTIVE INVESTIGATION OF TRENDS IN POPULATION-DENSITY AND BREEDING SUCCESS

(1) British Trust for Ornithology Common Bird Census and Nest Record Scheme data were analysed for magpies and fifteen species of songbird: blackbird Turdus merula L., song thrush Turdus philomelos C. L. Brehm, mistle thrush Turdus viscivorous L., dunnock Punella modularis L., robin Erithacus rubecula L., chaffinch Fringilla coelebs L., greenfinch Carduelis chloris L., goldfinch Carduelis carduelis L., skylark Alauda arvensis L., wren Troglodytes troglodytes L., yellowhammer Emberiza citrinella L., blue tit Parus caeruleus L., great tit Parus major L., nuthatch Sitta europaea L. and starling Sturnus vulgaris L.. (2) Magpie numbers increased in Britain at an average rate of 4-5% year-1 from 1966 to 1986. Rates of increase of magpie numbers were highest in south-west England and in suburban and scrub habitats. (3) Songbird nest success did not decline between 1966 and 1986 in any of fifteen songbird species examined. Nest success increased in four species: song thrush, greenfinch, starling and yellowhammer. (4) Songbird nest success was not related to magpie density on farmland and woodland for comparisons either between regions or subdivisions of both habitat types. (5) In woodland, songbird numbers increased most when magpie numbers were high. (6) In woodland, songbird numbers increased most when magpie numbers increased most. (7) There was no evidence that increases in magpie numbers had any deleterious effects on songbird populations or breeding success. However, there may be effects which would not have been detected in this study.