Escape responses of cryptic frogs (Anura : Brachycephalidae : Craugastor) to simulated terrestrial and aerial predators

Cryptic prey may increase likelihood of being detected if they move. When approached by predators, they must assess probabilities of survival if they remain immobile or attempt escape. Probability of survival is the joint probability of being detected, attacked if detected, and captured if attacked. We studied escape responses of several species of cryptic Craugastor (= Eleutherodactylus) frogs to simulated ground and aerial predators by varying elevation angle of attack. Frogs were predicted to escape more frequently when attacked from higher angles because a predator attacking from above on a trajectory leading directly to the prey is more likely to have detected and be attacking than a predator approaching directly, but horizontally. Frogs approached horizontally rarely jumped. The proportion of frogs that jumped increased as attack angle increased, and the proportion that turned or twitched was greatest for 45 degrees approaches. Distance jumped did not vary among attack angles. Escape was directed away from the object approaching at 45 degrees, but was random with respect to the frog's orientation during vertical approaches. Variation in escape tendency may occur because risk increases as attack angle increases, possibly because risk of being detected from above is greater and/or aerial predators are more efficient.