Strawberry poison-dart frogs respond stronger to small rivals

A ‘blue-jean frog’ interacts with a model ‘rival’ made by the group. The plastic bag contains a speaker that played a male call.

Study by Nate Bennett, Glennon Langan, and Elizabeth Luotto.

In species with low predation rates, intraspecific competition is often more important to reproductive success and can lead to strong territorial behavior. This behavior is observed in male Oophaga Pumilio, commonly known as the Strawberry Poison Dart Frog, which occupy 2-3 m² breeding areas with high female density. Males can be identified by the chirping they use to defend their territory, an honest signal of their fighting ability. We looked at how the perceived strength, defined as size of the frog and its chirping volume, of a competitor influences the motivation of a defending male to protect their territory. We placed a clay frog model and Bluetooth speaker within another male’s territory and mimicked the call of the frogs. Then, we measured the latency, duration, and number of calls from the defending frog.  We found that 88% of defending frogs approached our model and that 93% vocally responded. A two-way ANOVA showed a significant interactive effect of size of the model frog and call volume on the number of call responses.  Other two-way ANOVAs showed a significant relationship between model size for both latency and call duration. These results suggest that defending male frogs respond more quickly and often to smaller competitors and that size may be a greater motivator than volume. We hypothesize that because vocal calls are an honest signal of fighting ability, they may be sufficient to defend territory when the intruder is small and quiet and suggest this as a future area of research.

Nate Bennett and Elizabeth Luotto (Glennon Langan not pictured) observe interactions between frogs and models (shown on right).