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1 May 2018 Comparisons of Foraging Behavior and Energetics by Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) Across Three Microhabitats
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Abstract
Long-legged wading birds (Family Ardeidae) feed in a variety of aquatic microhabitats, all of which have the potential to alter foraging behavior based upon different abiotic and biotic factors such as the energetic value of the prey present. Foraging behavior in three microhabitats was measured for Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) from May-August 2017. For both species, we completed six hours of observations in rivers, ponds, and weirs (small waterfalls). We recorded strike rates and capture rates per minute, and prey lengths relative to culmen length. Foraging efficiencies were then calculated, which we defined as successful strikes divided by total strikes. Lengths, weights, and energetic values were estimated for all captured prey. Snowy Egrets (55%) had higher overall foraging efficiencies than Great Egrets (48%). Foraging success for both species also differed by microhabitat. Snowy Egrets had significantly higher foraging efficiencies than Great Egrets in rivers and weirs, but not in ponds. There were also significant differences in strike rates, capture rates, and prey sizes both by microhabitat and between species. Both species had the highest foraging efficiency at weirs. Snowy Egrets had higher strike rates and capture rates than Great Egrets in all three microhabitats. However, Great Egrets caught fish in all three microhabitats that were higher energetic value than those caught by Snowy Egrets. Aggression rates at weirs were about three times higher than at both rivers and ponds.
Abigail C. Harper and Alan D. Maccarone "Comparisons of Foraging Behavior and Energetics by Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) Across Three Microhabitats," Transactions of the Kansas Academy of Science 121(1-2), (1 May 2018). https://doi.org/10.1660/062.121.0222
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