Studies must be performed throughout the year to determine how the seasonal energy requirements of Snowy Egrets (Egretta thula) and Great Egrets (Ardea alba) change. Foraging behavior was quantified during the breeding season in Kansas and during the non-breeding season in Florida using energetic algorithms and scan sampling. Fifty-eight percent (n = 287) of breeding Snowy Egrets were observed ambulating while 51% (n = 271) of non-breeding Snowy Egrets were observed loafing. Standing foraging was the most commonly observed behavior among Great Egrets in both the breeding (54%, n = 91) and non-breeding (38%, n = 164) seasons. Behavior was dependent on season for both Snowy Egrets (χ2 = 200.1, P < 0.001) and Great Egrets (χ2 = 187.4, P < 0.001). During the breeding season, Snowy Egrets expended 0.13 ± 0.06 W (Watts) in rivers and 0.08 0.02 W at weirs. During the non-breeding season Snowy Egrets expended 0.06 ± 0.01 W. During the breeding season Great Egrets expended 0.11 0.02 W at both weirs and in rivers, and 0.09 ± 0.02 W during the non-breeding season (F2,46 = 7.86, P < 0.0012). Snowy and Great egrets appear to vary their caloric demand on aquatic systems over the annual cycle. However, the quantity of energy derived from an ecosystem should not be the only factor taken into consideration in determining the value of that ecosystem.
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Vol. 36 • No. 1