Factors influencing failure strikes to terrestrial and aquatic prey animals in Gloydius spp. in the field
Department of Zoology
Graduate School of Science
Sakyo, Kyoto, Japan
Water and air have different physical properties. Accordingly, behaviors of animals within each medium largely differ. Therefore, researchers have attempted to clarify how different the feeding behavior and performance of species feeding in both media are. However, no study has examined differences of factors influencing the outcome of snake-prey interactions under natural conditions in different media or at the boundary between them. Recent field studies on rattlesnake-mammalian prey interactions have demonstrated that predation success is determined not only by performance of strikes (acceleration or velocity) but also by strike accuracy (whether strike reaches the place where the prey is positioned) and reactions of prey (latency to start to dodging). In this study, we focused on predatory strikes of two species of Gloydius in Japan, G. blomhoffii and G. tsushimaensis, feeding on various vertebrates from fish to mammals. Our goal is to clarify any difference of strike kinematics, strike success rate, and factors influencing the outcome between terrestrial strikes to frogs and mammals (TS) and aquatic strikes to fish (AS) under natural conditions. We used combined methods of radiotelemetry and fixed-videography to record predatory strikes. TS and AS were kinematically different from each other. Some of AS were lateral strikes and included successive strikes, whereas all TS were performed as a single frontal strike. Strike success rate was lower in AS than in TS. In failure strikes, the rate of accurate strikes was lower in AS than in TS. In these accurate strikes, reaction time of prey was shorter in AS than in TS. These findings indicate that the factors influencing strike outcome are different between TS and AS. Pitvipers may have difficulties especially in recognizing aquatic prey animals accurately and thus adopt different striking tactics in aquatic strikes. We discuss implications of the differences between TS and AS.