The Role of Profitability in Snail Kite Foraging

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Abstract
(1) The foraging strategies of one pair of breeding and forty-five nonbreeding snail kites (Rostrhamus sociabilis Vieillot) were studied in relation to predictions of Royama''s (1970) model of niche hunting by profitability in Guyana, South America. (2) The study did not corroborate or refute the prediction that profitability is the major foraging mechanism. (3) Although the birds tended to spend most foraging time in the most profitable habitat, they had difficulty discriminating among slight differences in habitat profitability. (4) All kites apparently sampled habitats to monitor profitability trends which changed over time, with peaks at 06.00-08.00 and 18.00-20.00, and a low at 12.00-14.00. (5) No spatial choices were detected relative to habitat-profitability changes. The relatively large sizes of the habitats may have contributed to this lack of preference switching due to spatial changes in profitability. (6) However, kites did concentrate their hunting efforts in the habitat with the highest prey density. (7) Diet differences between adults and juveniles were associated with differences in handling times for the two age classes. Adults took significantly larger apple snails (Pomacea doliodes Reeve) than did juveniles and spent significantly less time handling these snails, but it is not known if these differences resulted from differences in handling time, as predicted by the model. (8) The breeding pair took significantly larger snails back to the nest than they consumed. This behaviour may be better explained by the size-distance relations of central place models than by Royama''s handling time to prey size relationships.