When food is not limiting, competition for high quality nesting sites can limit the density of breeding birds. Quality nesting sites must provide structural support for nests as well as to offer effective protection against predators and unfavorable weather. Anthropogenic influences can alter the structure and composition of vegetation available for nest sites, thereby providing birds with novel habitat. We examined the effects of colony structure and nest position on the reproductive success of wading birds nesting at Lake Okeechobee to determine if colonies in anthropogenic habitat (spoil islands) had lower reproductive rates than colonies in natural habitat (willow islands). During the 2015 breeding season, we measured reproductive success and nest site characteristics at each colony. We used logistic-exposure modeling in an information-theoretic framework to determine the most important factors affecting daily survival rate (DSR) of nests.
Results/Conclusions
Nest survival rates did not differ significantly between the two colony types. The best model predicting DSR included nest height, distance to canopy, and type of substrate species (invasive or noninvasive). Nest survival rates were higher for nests placed farther from the canopy edge, higher from the ground, and in noninvasive substrate. Results indicate that spoil islands are capable of providing nesting habitat comparable to natural islands in some years. However, factors that led to a lower DSR, (e.g., invasive plants and short vegetation), also tend to be more prevalent on spoil islands, so over a longer time we would expect to see differences in DSR emerge.