Estratégias de forrageamento e seleção de presas pelo gavião-caramujeiro (Rostrhamus sociabilis)

Abstract

Among the factors that contribute to the structure, balance and resilience of the ecological systems, one can list the specie‟s resource exploitation strategies such as foraging and the intricate ecological predator-prey relationships. The Snail kite (Rostrhamus sociabilis) is the only bird of prey specialized in ingesting snails of the Pomaceae genus, the Apple snail. This study aimed at deepening our understanding on the complex ecological system involving the Snail kite, and its main prey, assessing the environmental and behavioral factors that may act on its foraging, investigating the selection of prey size by the Snail kite and comparing it to another syntopic molluscivore bird, the Limpkin Aramus guarauna. We run 60 hours of behavioral observations from December 2019 to September 2020 at the Botanical Garden of the Universidade Federal de Juiz de Fora. Our data revealed that the Snail kite‟s success at capturing its preys increased during cloudy days, when the bird performed the still-hunting foraging strategy, and when the local population of the species was larger. Moreover, through comparing the size of snails preyed by Snail kite and those living in the lake showed that the bird selected for the larger prey. Finally, the R. sociabilis and A. guarauna preyed on similar-sized snails. The Apple snail depends on detecting sudden light intensity variation to respond to an oncoming predator. Thus, the increased foraging success of the Snail kite in cloudy periods (i.e., diffuse light), is reasonably related to the limited sensorial and escaping ability of the Apple snail in such light condition. On its turn, the success of the still-hunting strategy suggests both the influence of environment structure (e.g. perch availability) and prey distribution. Additionally, by selecting larger prey, the Snail kite secures higher caloric intake while reduce energy expenditures, as suggested by the optimal foraging theory. Finally, the similar size of the Snail kite and the Limpkin preys suggest that the local snail population supports the nutritional needs of both predators, thus suggesting the species share instead of competing for this food source. In contributing to the natural history of the Snail kite, this study highlights new in-depth research aiming at better understandings of the role of the species on the population control of the Apple snail, its migratory behavior, and the ecological factor acting on the behavior and ecology of a predator that, for having a specialized diet, is more prone to suffer consequences of natural or human-caused/induced environmental changes.