FACTORS INFLUENCING BURROWING OWL REPRODUCTIVE ;PERFORMANCE IN CONTIGUOUS SHORTGRASS PRAIRIE

Abstract

We analyzed Burrowing Owl (Athene cunicularia) reproductive performance (i.e., clutch size, brood size, and number of young fledged) in relation to nest and colony factors in Buffalo Gap National Grassland, South Dakota. We monitored 129 pairs of Burrowing Owls in 43 prairie dog (Cynomys ludovicianus) colonies in 1999 and 143 pairs in 45 colonies in 2000. Mean clutch size was 7.2 and ranged from 3–10 eggs. Pairs averaged 2.6 fledglings per nesting attempt and 76% of the nesting pairs were successful in fledging at least one young. Abandonment appeared to be the primary cause of nest failures. Variables measured at the colony level explained more (34–70%) of the variability in reproductive performance than did variables measured at the nest level (7–33%). In general, Burrowing Owls that arrived early, initiated clutches sooner, and either nested at greater distances from nearest neighbors or had fewer owl nests within 250 m of the nest burrow, had larger clutches, larger broods, and more fledglings. Seventy percent of prairie dog colonies were occupied by owls; most (85%) unoccupied colonies were <10 ha in size. Larger prairie dog colonies supported greater numbers of owl nests and consequently produced more total fledglings than did smaller colonies (P < 0.001).