Effects of Increased Sound Level of Advertisement Calls on Calling Male Frogs, Eleutherodactylus coqui

Abstract

If calling male Eleutherodactylus coqui are intolerant of other calling males nearby, then the sound level of advertisement calls can function as a nocturnal spacing mechanism for calling frogs. To investigate this hypothesis, we played advertisement calls to 23 individual calling males in the forest at El Verde, Puerto Rico. We played calls at six sound pressure levels from 75 to 102 decibels. The mean number of aggressive calls increased and advertisement calls decreased as sound pressure level increased. The ratio of advertisement to aggressive calls at each level decreased as sound level increased. Both behavioral responses and call types varied among individuals. Most frogs became silent or moved away as sound pressure level increased beyond 89-94 decibels. Calling males apparently space themselves by mutual avoidance and fight only in defense of retreats or nests. We propose that short multinote calls are the primary aggressive cells (encounter calls), and that the co call serves in establishing vocal interactions with neighboring males, and possibly in signal interference.