EFFECTS OF INCREASED SOUND LEVEL OF ADVERTISEMENT CALLS ON CALLING MALE FROGS, ELEUTHERODACTYLUS-COQUI

If calling male Eleutherodactylus coqui are intolerant of other callin g males nearby, then the sound level of advertisement calls can functi on as a nocturnal spacing mechanism for calling frogs. To investigate this hypothesis, we played advertisement calls to 23 individual callin g 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 agg ressive calls increased and advertisement calls decreased as sound pre ssure level increased. The ratio of advertisement to aggressive calls at each level decreased as sound level increased. Both behavioral resp onses and call types varied among individuals. Most frogs became silen t or moved away as sound pressure level increased beyond 89-94 decibel s. Calling males apparently space themselves by mutual avoidance and f ight only in defense of retreats or nests. We propose that short multi note calls are the primary aggressive cells (encounter calls), and tha t the ''co'' call serves in establishing vocal interactions with neigh boring males, and possibly in signal interference.