Density and Reproduction of Burrowing Owls Along an Urban Development Gradient

Millsap, Brian; Bear, Cindy

We studied population density and reproductive success of a Florida burrowing owl (Athene cunicularia floridana) population on a 35.9-km^2 study area that spanned a residential development gradient ranging from 80% of lots with houses in Lee County, Florida, 1987-90. We observed 785 breeding attempts at 264 unique nest sites in an increasing population of owls. Linear regression indicated that nest site density (6.9 pairs/ km2 in 1990) increased until 45-60% of lots were developed before decreasing. Overall nest success (69.6 +- 4.2%; x +- SE) did not vary along the development gradient, however the proportion of nests that failed from human-related causes increased with increasing development. The number of young fledged per nest site increased until development exceeded 45-60%, then stabilized. The number of young fledged per successful nest decreased as development increased above 60%. Burrowing owls that nested on lots where home construction was occurring fledged more young if a >10-m buffer from disturbance was provided around the nest burrow. Burrowing owls nesting in sodded yards of homes fledged fewer young than nests in vacant lots. Our results, combined with those of previous researchers, suggest that burrowing owls on our study area benefited from high prey densities around homes, but that increased human-cause nest failures and declines in the number of young fledged at successful nests in heavily developed areas offset the advantages of abundant prey.

Density and Reproduction of Burrowing Owls Along an Urban Development Gradient

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