Multimodal communication and spatial binding in pied currawongs (Strepera graculina)

To make accurate assessments about their environment, animals must integrate a variety of sensory cues into a single unified percept. The effects of redundant multimodal signaling may be equivalent to the responses elicited by each individual cue, or enhanced when cues are combined. Binding of two seemingly coupled cues can persist despite small spatial and temporal discrepancies in signal presentation, a phenomenon termed the ventriloquist effect. Our study had two aims: first, to test the cognitive ability of a territorial, forest-dwelling bird to bind two spatially disparate cues; and second, to define the processing of the acoustic and visual cues as having either equivalent or enhanced effects when presented together. We broadcasted pied currawong (Strepera graculina) vocalizations alone or in the presence of a model currawong situated either adjacent to, or far away from a speaker, to free-living currawongs. The number of locomotive events and the average standard deviation in the distance from the speaker maintained by the focal currawong were greater in response to "far" than "close" treatments. Additionally, the average standard deviation of the distance to speaker for the uni-modal, speaker only treatment was similar to "far" responses. These findings support our hypothesis that currawongs cognitively bind two stimuli in close spatial proximity. In nature, this would result in an enhanced level of response toward territorial intruders. Our study was novel in its attempt to assess cognitive processes involved in the integration of spatially disparate bimodal signaling events in free-living birds.