Water-level fluctuations determine the ecological function of shallow lakes and wetlands. In the Anthropocene, modifications to freshwater systems are extensive and likely to become more pervasive on a global scale. As top predators in wetland ecosystems, wading birds (Pelecaniformes and Ciconiiformes) are reliable indicators of the biotic conditions at multiple trophic levels, thereby reflecting an ecosystem response to water-level changes. We used a historic nesting record dating back to 1977 and an information-theoretic approach to identify environmental factors most important for predicting numbers of nesting pairs at Lake Okeechobee, a highly managed reservoir in Florida.
The top three models accounted for 71% of the Akaike weight. Model variables included area of willow (Salix spp.) for nesting substrate, January 1 lake stage as a measure of maximum lake surface area, and foraging habitat availability over the nesting season. Collectively, the results suggest the number of nesting pairs was greatest when area of nesting substrate was high and water levels were moderate. Nest numbers dropped when either nesting substrate or foraging habitat was limited. This information has important implications for lake management because water managers aim to set hydrologic regimes that meet the water needs of the natural ecosystem while also providing water supply and flood protection for people.