How, when, and where to perform visual displays:: The case of the Amazonian frog Hyla parviceps

We performed intrusion experiments and observed the course of 13 male-male agonistic interactions to gather information on the communicative role of visual signaling in the Amazonian tree frog Hyla parviceps. To obtain information on the ecological context potentially associated with visual signaling, we performed nightly censuses of calling activity and tested whether males differentially used microhabitats in relation to properties that affect both acoustic and visual communication. Among seven behaviors performed by males, two were visual displays. Foot-flagging displays and advertisement calls were used at a similar rate and at similar distances between interactants. Arm-waving displays were less common and used at a closer range than foot-flagging displays. The analysis of a dyadic transition matrix revealed that foot flagging significantly elicited foot-flagging displays by the opponent frog. Furthermore, resident males produced more arm wavings and calls than intruders, although the latter difference was not significant. We conclude that male H. parviceps respond to intruders by combining advertisement calls and visual displays, and that visual signals may serve functionally as a spacing mechanism. Comparing the properties of perches used by calling males with a random sample of available perches indicates that males prefer perches surrounded by denser and higher vegetation. Furthermore, calling activity occurred during or shortly after heavy rains and coincided with calling activity of several co-occurring species of hylid frogs, which probably decreases the locatabilitv of calling males. We suggest that, under these conditions, the simultaneous production of auditory and visual signals may momentarily increase a sender's locatability when a conspecific receiver is detected.