Frog or Fruit? The Importance of Color and Shape to Bird Predators in Clay Model Experiments

Clay model experiments are commonly used to measure natural rates of predation and have become an important method in studying predator avoidance of aposematic frogs. Previous clay model experiments have demonstrated that conspicuous coloration in dendrobatid frogs is an effective deterrent to avian predators. It is generally assumed that predators recognize clay models as frogs, but few studies have examined this hypothesis. Certain aposematic frogs are similar in color to fruits on the forest floor, and it is possible that frugivorous or omnivorous birds perceive clay models as fruit. In the present study, we further investigate aposematism in Oophaga pumilio and specifically examine the importance of model shape and color. We assessed natural avian predation rates using clay models, which were either red or brown in color, and frog or ball (fruit) shaped. Overall, avian predation was significantly higher on red ball-shaped models when compared to red frog-shaped models. Brown frogs were also more likely to be preyed upon than red frogs. The omnivorous Great Tinamou (Tinamus major), however, exhibited no preference for frog color. Feeding naturally on fruits and seeds, tinamous in our study preferred and attacked red ball models more frequently, suggesting that they recognized these models as fruits. Collectively, our results provide evidence that birds distinguish between shapes and colors when making decisions about predation and that these attacks are dependent on the dietary preference of the predator. Clay model studies should take into account both color and shape of models, and consider that predation rates are likely dependent on the species assemblages present at a location and their specific dietary preferences.