Vegetation and Soils of Burrowing Owl Nest Sites in Conata Basin, South Dakota

Burrowing Owls (Athene cuniculuriu) in southwestern South Dakota frequently use the burrows of black-tailed prairie dogs (Cynomys ludovicianus) for nesting and escape cover.Coulombe (1971) emphasized the importance of understanding the role of burrow selection in relation to owl behavior, physiology, and overall ecology.He also suggested that availability of burrow sites may be the critical factor in Burrowing Owl population dynamics.ports indicate that from 8% to 60% of burrows previously occupied are re-used by Burrowing Owls (Wedgewood 1976, Gleason 1978).Rich (1984) reported that re-use of Re-use of nest burrows by owls has been reported in the literature, but data are limited (Rich 1984).Previous re-Our study was conducted from April through October 198 1.During April and May, we located Burrowing Owl nest sites by observing owls as they defended territories, gathered nesting material, and showed other breeding behavior (Thomsen 197 l), and eventually by seeing young.Prey remains, regurgitated pellets, and nesting material also helped in identifying burrows used as nest sites.We searched the entire area for nesting owls.We estimated canopy cover and height of surrounding vegetation, soil texture, distance to water, burrow diameter, topography, and aspect at confirmed nest sites and at adjacent unoccupied burrows.A "non-nest burrow" was defined as the closest burrow to a nest burrow that was not occupied by prairie dogs, and that could be used by owls.We believed this procedure would provide more accurate information than a random selection of vacant burrows over the entire study area.Owls presumably need search only a relatively small area before finding a suitable burrow.were estimated in a 2-by 5-dm plot spaced at l-meter intervals along each transect line (Daubenmire 1959).The height of the tallest plant in each plot was measured to We estimated plant canopy cover at each nest and adjacent non-nest burrow along four 20-m line transects originating from the center of each burrow.One transect line was oriented toward each of the four cardinal directions.Cover class of each plant species, bare ground, and litter nest sites by Burrowing Owls in sot¢ral Idaho ranges the nearest centimeter.Vegetation was sampled during the from 23% to 49%.Rich noted that owls often abandon last week in May and the first week in June.seemingly suitable nest sites for no apparent reason.Prairie dog activities often result in a complete absence of vegetation around their burrows and short vegetation in the prairie dog colony (Bonham and Lerwick 1976, Hansen and Gold 1977).Vacant burrows in Conata Basin quickly revegetate with annual forbs and eventually perennial grasses completely covering the burrows (pers.observ.).Changes in vegetation on abandoned prairie dog burrows could influence Burrowing Owl use.Furthermore, Coulombe (1971) suggested that the owls modify rodent burrows as nest sites.This suggests that soil characteristics may also be important in owl nesting ecology.