© 1997 Walt Dineen Society

Walt Dineen Society Annual Conference '97

Session V: Bird Studies Abstract #: 97505

Johanna Salatas and Peter Frederick
University of Florida, Department of Wildlife Ecology&Conservation Gainesville, FL 32611-0430


Due to extensive modifications of Everglades hydrology, the number of nesting attempts of all species of wading birds has declined by over 90%. Food availability may be the single most important factor that limits the distribution and nesting success of wading birds. Modeling projects designed to guide efforts to restore productive wading bird populations in the Everglades require accurate estimations of nestling food requirements. To date, the energetics of nestling wading birds remains poorly documented, simply because the logistics of measuring food intake have been difficult to obtain in the field. We have employed the labeled water technique in order to determine food intake in free-ranging Snowy Egret (Egretta thula) nestlings. After injecting nestlings with tritiated water and extracting blood samples in 5-d intervals, the labeled water technique, which is efficient and 95% accurate, allows us to calculate the water turnover rate. Because the water content of wading bird prey items in the Everglades is well known, the water turnover rate can be used to estimate prey consumption in nestlings. During the 1996 breeding season, we collected data from three sites in Water Conservation Areas 3A and 3B. Our results show that food intake can be measured in Snowy Egret chicks and the data imply that geographic differences do not seem to account for differences in the food amount delivered to chicks. Food amount strongly influences chick mass, independent of chick age and hatch order. Our results indicate that food amount is critical to the residual mass and possibly the fledgling condition of ciconiiform chicks which could influence post-fledging survival. We anticipate that these relationships will become better developed and more robustly tested during the 1997 breeding season.


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