Animal acoustic signals play seminal roles in mate attraction and regulation of male spacing, maintenance of pairbonds, localization of hosts by parasites, and feeding behavior. Among vertebrate signals, it is becoming clear that no single stereotyped signal feature reliably elicits species-specific behavior, but rather, that a suite of characters is involved. Within the largely nocturnal clade of anuran amphibians, the dart-poison frog, Epipedobates femoralis, is a diurnal species that physically and vigorously defends its calling territory against conspecific intruders. Here we report that physical attacks by a territorial male are provoked only in response to dynamic bimodal stimuli in which the acoustic playback of vocalizations is coupled with vocal sac pulsations, but not by either unimodal cues presented in isolation or static bimodal stimuli. These results suggest that integration of dynamic bimodal cues is necessary to elicit aggression in this species.animal communication ͉ territorial defense ͉ anuran ͉ amphibian ͉ Dendrobatidae

The mechanisms by which the brain binds together inputs from separate sensory modalities to effect a unified percept of events are poorly understood. This phenomenon was studied in males of the dart-poison frog Epipedobates femoralis. These animals physically and vigorously defend their territories against conspecific calling intruders. In prior field studies with an electromechanical model frog, we were able to experimentally evoke this aggressive behavior only when an auditory cue (advertisement call) was presented simultaneously with a visual cue (vocal-sac pulsations). In the present field experiments, we used a modified version of the electromechanical model frog to present territorial males with visual and auditory cues separated by experimentally introduced temporal delays or spatial disparities to probe temporal and spatial integration in this animal. In temporal integration experiments, bimodal stimuli with temporal overlap during calling bouts consistently evoked aggressive behavior; stimuli lacking bimodal temporal overlap were relatively ineffective at the same task. In spatial integration studies, despite presenting the components of the bimodal stimulus with an initial spatial disparity of up to 12 cm, fighting behavior persisted. These results demonstrate that temporal and spatial integration may be reliably estimated in a freely behaving animal in its natural habitat and that we can use aggressive behavior in this species as an index of cross-modal integration in the field.animal communication ͉ territorial defense ͉ anuran ͉ amphibian ͉ Dendrobatidae

As a neuroethologist, Bob Capranica strongly encouraged his students to study animals in their natural habitat in order to truly understand the behavioral rules underlying acoustic communication. This study was one of many inspired by those lessons. Male anuran vocalizations serve to attract conspecific females and to regulate male spacing through territorial interactions. In response to playback of a conspecific call, some male frogs have been reported to alternate their call with the perceived stimulus or shift their call-dominant frequency to avoid acoustic interference, or add call notes to signal an increased state of aggression. In some species, males orient toward the sound source followed by physically approaching the loudspeaker. Although natural fighting behavior between conspecific males has been observed in the field, it has not heretofore been possible to elicit with loudspeakers broadcasting sounds. In this playback study of the Brilliant-thighed dart-poison frog (Epipedobates femoralis) in French Guiana, we used an electromechanical model to provide realistic bimodal cues (acoustic and visual) to calling males. Our data suggest that agonistic behavior could be evoked in territorial males only when both acoustic and visual cues were presented simultaneously. [Work supported by grants from NIH (PMN) and Austrian Science Foundation (WH).]