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Flooded rice fields, which occupy half of the total agricultural land in Japan, are known to be foraging habitats for waterbirds. We investigated the use of various fallow fields by birds in midsummer, when rice fields are generally full of grown rice plants and are of little use for foraging waterbirds. We distinguished four types of fallow fields based on the ground cover and vegetation: (i) tall‐grass fields; (ii) wet short‐grass fields; (iii) dry fields; and (iv) flooded open fields. In August 1998 we counted birds four times in 19 survey plots of fallow fields and in seven plots of rice fields in Ibaraki Prefecture, Japan, where 82% of the farmlands are devoted to rice production. We observed 590 individual birds of 22 species, of which 15 species were waterbirds, mostly herons and shorebirds. Flooded open fields supported the largest number of species and the highest bird density, while rice fields supported the fewest. Within flooded open fields, herons preferred open‐water areas, while shorebirds used bare ground most often. Wet short‐grass fields looked similar to flooded open fields, except for the amount of short grass, but supported far fewer birds than flooded open fields. The number of birds in dry fields was comparable to that in flooded open fields, but most of the birds were ground‐foraging passerines. Our limited dataset suggests that fallow fields can serve as valuable supplemental habitats for waterbirds during summer, if they are appropriately managed to preserve flooded open fields and smaller areas of other habitats.

Abstract. Two segments of rice fields (0.4 ha each) in the coastal rice-producing region of Lake Kasumigaura, central Japan, were experimentally flooded from December to February (non-cultivation season), and bird abundance and macroinvertebrate availability in the fields were compared with those in unflooded rice fields and continuously flooded lotus fields. No waterbirds were recorded in the unflooded fields, but the experimentally flooded fields attracted Northern Lapwing Vanellus vanellus and snipe Gallinago spp., probably due to higher numbers of Tubificidae, Insecta (except Chironomidae) and Hirudinoidea in the soil and the water on the fields. Snipe were more abundant in unplowed flooded fields than plowed ones, indicating the importance of leaving rice stubble and post-harvest shoots as shelter for these secretive foragers. The flooded rice fields did not attract fish-eating waterbirds such as egrets Egretta spp., herons Ardea spp. or kingfishers Alcedo atthis, which occasionally appeared in the lotus fields. This was, probably because water pumped on to the experimentally flooded fields provided few fish or tadpoles. Landbird abundance also differed significantly among the field types. Unflooded fields supported more Skylarks Alauda arvensis and Siberian Meadow Buntings Emberiza cioides than others, whereas flooded fields were preferred by Water Pipits Anthus spinoletta. Lotus fields attracted Dusky Thrushes Turdus naumanni, White Wagtails Motacilla alba and Japanese Wagtails M. grandis. The results indicate that flooding fields in a dry riceproducing region in winter provides many water-and landbird species with suitable habitats, and contributes to increasing the diversity of the wintering bird community.

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