Differential Snail-Size Predation by Snail Kites and Limpkins

Snail kites (Rostrhamus sociabilis) and limpkins (Aramus guarauna) fed exclusively on apple snails (Pomacea dolioides) in three meadows on coastal Guyana, South America. These meadows were not exploited by other conspicuous snail eating predators. Thus, I analyzed the relationships among the sizes of shells remaining after predation by snail kites and limpkins, and the sizes of live snails in the meadows. Snail kites ate snails that were larger than those eaten by limpkins from two meadows, but the sizes did not differ in a third meadow. Although variability in the average sizes of snails available to the predators occurred among meadows, kites consistently captured snails that on average were larger than were those available for predation, except for the aforementioned third meadow. Limpkins, however, consistently took snails that were smaller than what was available in the meadows, although the difference was significant only once. Differences in the sizes of snails eaten may be due to the influence of snail respiratory behavior, snail parasite loads, and substrate conditions on snail antipredator behavior, and also to differences in foraging behavior of snail kites and limpkins. Significant linear relationships between snail parasite load and time they spent on the surface, and burrowing rate respectively explained much of the differential snail size predation by kites and limpkins in two of the three meadows. Additionally, limpkins could impact the future opportunities of snail kites to obtain large-sized snails, because limpkins captured smaller snails, thereby denying snails the opportunity to grow to the sizes kites ate. Future studies of the potential role of resource partitioning by sympatric species pairs would yield more insights if the studies were longterm and focus on the mechanisms that cause dietary shifts.