Abstract
The Least Tern (Sternula antillarum) is a colonially nesting shorebird that breeds across the United States. Because it traditionally nests on open beaches, it is susceptible to coastal development and other anthropogenic encroachments. As a result, the Least Tern has lost nesting habitat throughout most of its range, and in the absence of natural ground habitat, it now often nests on flat, gravel-covered rooftops. I studied reproductive success of Least Terns on beaches and roofs in southwest Florida and have (1) quantified differences in productivity between natural and manmade colony sites and (2) described physical and ecological characteristics at Least Tern colonies. Terns at beach colonies hatched a smaller percentage of eggs and produced fewer fledglings per pair than did terns at roof colonies. Differences between pooled beach and rooftop success rates were not statistically significant, but differences between individual colony sites were, indicating the changeable, stochastic nature of success and failure in Least Tern colonies. Specific factors affecting beach and roof success varied with site topography, local weather, predator species, and human disturbance regimes. Such variation among colony sites indicates that while roofs may be a viable habitat that increases the productivity of the Least Tern population in southwest Florida, for effective management colonies must be assessed for site-specific characteristics that can affect reproductive success. Although current construction practices are replacing gravel covered roofs, those that remain available to nesting Least Terns appear to be worth monitoring. If they are replaced in the future, it is important to know how their loss will affect the productivity of regional Least Terns; if the gravel is left, reproductive success might be enhanced with simple modifications to rooftops.
