Habitat use by three Acrocephalus warblers in an intensively used farmland area: the influence of breeding patch and its surroundings

Abstract

Habitat use by the sedge warbler Acrocepha- lus schoenobaenus, reed warbler A. scirpaceus and marsh warbler A. palustris was studied during 1998- 2000 in an intensively cultivated agricultural landscape in western Poland. The birds occupied mid-field marsh patches (0.05-9.84 ha) and drainage ditches. Using logistic regression models, habitat preferences for particular patch type, characteristics of breeding patch vegetation and surrounding crop type were investi- gated. All habitat measurements were done within 50- m radius circles around breeding territory centers. The most important factors that influenced species distri- butions were the proportions of particular habitats within patch area and the type of surrounding crops. Sedge and reed warblers preferred areas with a high proportion of reeds and meadows. Marsh warblers avoided emergents other than reeds, and favored herbaceous vegetation and bushes. Open water areas positively affected reed warbler distribution. Crop type had a significant influence on within-year territory distribution and changes in between-year occupation pattern. In general, birds preferred to settle near fields of oil seed rape, while root crops and spring cereals were avoided. Breeding patch type and structure of reedbeds had relatively little influence on the distri- bution of breeding territories. The results obtained show that the surrounding landscape may significantly influence habitat use of species breeding in habitat islands in farmland. Depending on their structure and food resources, crops might have different value to the birds.