Bird use of rice field strips of varying width in the Kanto Plain of central Japan

Bird communities in flooded rice strips of different widths were surveyed in 71 fields around Lake Kasumigaura, on the Kanto Plain (central Japan). Strips categorized into four width classes (<50, 50–100, 100–300 and >300 m) and two locations (core >100 and <100 m from edges) were censused from May to July 1998, and mean species number and density of birds were compared. Both density and mean species differed significantly between classes, strips >300 m wide favoring bird diversity and number of marsh and grassland species. Breeding skylarks and fan-tailed warblers hardly occurred in fields adjacent to edges. Strips <50 m wide were not suitable feeding site of egret species (Ardeidae), but supported diurnal activity of black-crowned night herons and species requiring both rice fields and adjacent environment. As a consequence, bird conservation in rice field strips needs to consider both their width and location within the environment.