Nesting substrate and water-level fluctuations influence wading bird nesting patterns in a large shallow eutrophic lake
Water-level fluctuations determine the ecological function of shallow lakes and wetlands. 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 that were most important for predicting the number of wading bird nests at Lake Okeechobee, a highly managed reservoir in Florida. The three top models accounted for 71% of the Akaike weight. Model variables included area of willow (Salix spp.) for nesting substrate, maximum depth of the lake on January 1, and foraging habitat availability over the nesting season. Collectively, the results suggest that the number of nests was greatest when area of nesting substrate was high and water levels were moderate (3.9–4.4 m). Nesting substrate was greatest when water levels fell below 3.9 m at least once every three years. Nest numbers dropped when either nesting substrate or foraging habitat was limited. This study identifies key hydrological parameters that support large populations of breeding wading birds and thus promote healthy, functioning wetland ecosystems.
KeywordsForaging ecology Habitat availability Hydrology Reservoir management Salix
We thank our field research crews and fellow researchers who assisted in collection of field data: G. Akerman, R. Botta, J. Bredlau, E. Dancer, M. Dillon, B. Farmer, A. Galle, R. Hartman, P. Heidemann, F. Marenghi, D. Marx, J. Michaud, K. Norris, and E. Plazarte. We benefited from discussions with B. Botson, C. Callaghan, P. Gray, C. Hanlon, G. Herring, J. Klassen, and B. Sharfstein. SFWMD staff generously provided data on the locations and characteristics of wading bird foraging flocks. Funding for this research was provided by the U.S. Army Engineer Research and Development Center (Grant No. W912HZ-09-2-0022), the National Park Service (Grant No. J5297 05 0083), and Florida Atlantic University. Research techniques were approved by the Florida Atlantic University Institutional Animal Care and Use Committee (Protocol A10-30) and conducted under U.S. Fish and Wildlife Service Research Permit 23354.
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