Effects of nest dimensions on use of artificial burrow systems by burrowing owls

Although wildlife managers and researchers frequently use a variety of arti ficial burrow systems (ABS) to attract or supplement habitat for western bu rrowing owls (Athene cunicularia hypugaea), no previous studies have examin ed effects of ABS configuration on owl use, We examined choice of ABS confi gurations by nesting western burrowing owls in southwestern Idaho during 19 97-98. To assess potential selection for chamber size, we placed clusters o f 3 ABS around natural nest sites used 1995-97. Each cluster contained 3 bu rrows, each with a standard tunnel diameter but 3 different chamber sizes ( 707 cm(2) [small], 900 cm(2) [medium], and 1,750 cm(2) [large] of floor spa ce). To assess potential choice for tunnel diameter, we placed clusters of 2 ABS in suitable burrowing owl habitat. These clusters offered 2 tunnel di ameters (10 and 15 cm), each with a small chamber. Annual and combined dist ribution of use indicated that burrowing owls used ABS with large nest cham bers and 10-cm-diameter tunnels. We deterred no differences in clutch size or number of fledglings among chamber sizes, between tunnel diameters, or b etween cluster types (i.e., 2 or 3 ABS), although differences in number of fledglings between years existed for both types of clusters. Burrowing owls may use ABS with large chambers and small tunnel diameters to reduce negat ive effects of overcrowding, to gain the most favorable microclimate for de veloping juveniles, or to help deter larger ground-dwelling predators. Our results indicate that researchers and resource managers interested in manag ing burrowing owl habitat should consider ABS composed of (1) chambers with >900 cm(2) of floor space, and (2) 10-cm-diameter tunnels.