Mm. Stewart et Pj. Bishop, EFFECTS OF INCREASED SOUND LEVEL OF ADVERTISEMENT CALLS ON CALLING MALE FROGS, ELEUTHERODACTYLUS-COQUI, Journal of herpetology, 28(1), 1994, pp. 46-53
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.