Abstract
We investigated the use of various types of bridge as day roosts by several species of bats in Obihiro, Hokkaido. Eleven species belonging to six genera were found in the study area. Six species belonging to two genera used bridges as day roosts. The bridges were categorized into three types according to their structural characteristics. Bridges with flat undersurfaces were classed as flat-bottomed bridges; those with intersecting beams that formed deep cavities or cells on the undersurface were classed as cell bridges; and those with narrow parallel cavities on the undersurface were classed as stria bridges. Only cell and stria bridges were used as day roosts. Cell bridges were used more frequently than stria bridges. Bats created colonies in cell bridges, whereas almost all of the stria bridges were used as solitary roosts, particularly by juveniles. More species used stria bridges than used cell bridges. These results suggest that the type of bridge used by bats as day roosts depends on the bats' breeding stage. An increase in the use combined floorboard bridges, a new type of structure, may reduce the number of bridges potentially used by bats as day roosts.
