Multimodal signaling in fowl, Gallus gallus

Many social birds produce food-associated calls. In galliforms, these vocalizations are typically accompanied by a distinctive visual display, creating a multimodal signal known as tidbitting. This system is ideal for experimental analysis of the way in which signal components interact to determine overall efficacy. We used high-definition video playback to explore perception of male tidbitting by female fowl, Gallus gallus. Hens experienced four treatments consisting of multimodal tidbitting, visual tidbitting without sound, audible tidbitting without a male present, and a silent empty cage control. Hens took longer to begin food search when the display was silent, but the overall rate of this response did not differ among the multimodal, visual only or audio only playback treatments. These results suggest that the visual and vocal components of tidbitting are redundant, but they also highlight the importance of a temporal dimension for any categorization scheme. Visual displays also evoked inspection behavior, characterized by close binocular fixation on the head of the playback male, which is known to facilitate individual recognition. This may also allow hens to assess male quality. Such social responses reveal that tidbitting probably has multiple functions and provide a new insight into the selective factors responsible for the evolution of this complex multimodal signal.