Segregation in sizes of snails depredated by Snail Kites Rostrhamus sociabilis and Limpkins Aramus guarauna in southwestern Colombia

Abstract

The Snail Kite (Rostrhamus sociabilis) and the Limpkin (Aramus guarauna) feed almost exclusively on freshwater snails of the genus Pomacea. In order to evaluate the likelihood of competition between two populations of these species, we measured snails eaten by each and compared these measurements with those of live snails captured in the foraging habitats of the birds. The Snail Kite fed upon snails found floating in the open water of the wetland while the Limpkin captured those snails found in the floating mats of Water Hyacinth (Eichornia crassipes). Snails found on these plants were larger than those found in open waters, and the snails eaten by the Limpkin were also larger than those captured by the Snail Kite. We did not find evidence of prey selection by these species, judging from the proportion of prey sizes available in their respective habitats. Evidence indicates that each bird captures the snails as they occur in their habitats, which rules out interspecific competition for prey size. The snails constitute a very abundant resource in the wetlands occupied by these birds in southwestern Colombia, and this has allowed the increase of their populations over the past 40 years in the Cauca River valley.