Externally Attached Radio-Transmitters Have Limited Effects on the Antipredator Behavior and Vagility of Rana Pipiens and Rana Sylvatica

Abstract

Anurans display a variety of antipredator behaviors from flight and crypsis to defensive postures. External attachment of a radio-transmitter is a commonly used technique that could potentially interfere with the antipredator behavior of anurans. We investigated the effect of an externally attached radio-transmitter on the antipredator behavior and vagility of adult Northern Leopard Frogs (Rana pipiens) and adult Wood Frogs (Rana sylvatica). We simulated attacks by birds and snakes and used fluorescent powder to follow the path of individuals through natural habitats. Both species displayed a different frequency of behaviors in response to each predator, but the presence of a transmitter did not affect the frequency of antipredator behaviors. When carrying a transmitter, R. pipiens exhibited a different escape angle during attacks by simulated aerial predators and exhibited a change in the mean turn angle over 4-h movement paths. Rana sylvatica's escape behavior and vagility were unaffected by a transmitter during simulated attacks, although frogs with a transmitter did take more jumps per 4-h movement paths and followed straighter paths than did frogs without a transmitter. The body mass of the individual did not affect any of our behavior or movement metrics. Although most of our metrics did not change markedly in response to the presence of a transmitter, the subtle changes in vagility and escape behavior are analogous to the negative effects of externally attached transmitters seen in birds and mammals. These results suggest that transmitters may have consequences for the energetics, survival, and reproduction of anurans.