THE DISTRIBUTION OF PASSERINE BIRDS IN HEDGEROWS DURING THE BREEDING-SEASON IN RELATION TO CHARACTERISTICS OF THE HEDGEROW AND ADJACENT FARMLAND

1. Passerine birds were surveyed during the breeding season in hedgero ws on 46 farms in lowland England. The incidence of each species was r ecorded in 50-m lengths of hedgerow and various attributes of these he dgerow sections were also recorded. 2. Logistic regression models were fitted to the data to describe the effects on the incidence of 18 bir d species of the number of trees, hedge height and width, dominant pla nt species in the woody hedge, under the hedge and adjacent to the hed ge in the uncultivated strip, the number of woody species in a standar d length and other hedgerow characteristics. The effects of adjacent l and use and cropping, reduced use of pesticides on cereal field edges and the geographical location of the study farms were also included in the models. 3. Most bird species preferred tall hedges with many tree s, but there were some (dunnock, willow warbler and lesser whitethroat ) which preferred tall hedges with few trees and others (whitethroat, linnet, yellowhammer) which preferred short hedges with few trees. 4. The differences among bird species in response to a sevenfold reductio n in the height of hedges estimated from the models showed good agreem ent with the variation among species in the effects of severe hedge cu tting on bird populations at one farm observed in an independent study . 5. The incidence of six bird species was positively influenced by th e number of woody species in a standard length of hedgerow. 6. The inc idence of two bird species was significantly affected by the identity of the dominant woody plant species in the hedge and one species by th e identity of the dominant plant species at the base of the hedge. 7. Land use adjacent to the hedgerow, categorized as grass, tillage and r oadside, had a significant influence on the incidence of five species. However, there was no evidence of consistency among species in the di rection of effects. 8. The crops grown on tilled land adjacent to the hedgerow had a significant influence on the incidence of the blackbird . There was a significant degree of consistency among bird species in the ranking of crops, with oil-seed rape the most preferred and spring -sown cereal the least preferred. 9. The incidence of greenfinch, robi n and song thrush was significantly lower in hedgerows adjacent to aut umn-sown cereals which had received reduced levels of spraying of pest icides than in those adjacent to autumn-sown cereals which were fully sprayed. Most of the other species showed non-significant differences in the same direction. Most of the species studied also showed a non-s ignificant tendency towards higher incidence in hedgerows adjacent to spring-sown cereals with reduced spraying than in those adjacent to fu lly sprayed spring-sown cereals.