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1 November 2012 The Effects of Prey Density on Capture Times and Foraging Success of Course-Hunting Adult Snail Kites
Philip C. Darby, Ikuko Fujisaki, David J. Mellow
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Foraging-patch selection may be influenced by prey density, prey availability, and the energetic costs associated with searching for and capturing prey. Although prey density influences profitability, prey availability may be influenced by habitat and environmental characteristics. We made in situ observations of Snail Kites (Rostrhamus sociabilis) foraging on their exclusive prey, apple snails (Pomacea paludosa), in selected habitats and environmental conditions. We measured the time to capture a snail at 10 sites on Florida lakes (two sites sampled twice over different years for 12 data points total) and five sites in wetlands of the Everglades. Capture times had an inverse asymptotic relationship to snail density. As snail density increased from ∼0.1 to 0.2m-2, capture times declined from ∼600 to 200 sec; capture times leveled off to ∼75 sec between 0.4 and 1.4 snails m-2. Densities of emergent plant stems and water depths, which may influence capture times, were controlled for by site selection; analyses verified these factors had no effects. Snail Kites were significantly more likely to abandon a foraging bout if snail density was <0.2m-2. We interpret the results in the context of foraging for inconspicuous prey. Our data and other reports indicate ∼0.1–0.2 snails m-2 as an approximate threshold below which flight costs increase dramatically and fewer kites tend to forage. Our observations contribute to the limited information available on what constitutes prey density sufficient for the Snail Kite, and we discuss associated conservation implications for this endangered dietary specialist.

© 2012 by The Cooper Ornithological Society. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Philip C. Darby, Ikuko Fujisaki, and David J. Mellow "The Effects of Prey Density on Capture Times and Foraging Success of Course-Hunting Adult Snail Kites," The Condor 114(4), 755-763, (1 November 2012).
Received: 11 April 2011; Accepted: 27 April 2012; Published: 1 November 2012

capture times
Rostrhamus sociabilis
Snail Kite
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