It is relatively common in the animal kingdom that species will communicate with one another through more than one sensory modality; that is, they can combine auditory, visual, olfactory (smell), and other signal forms in their interactions with other individuals, just as how we may wave and shout someone’s name at the same time to better get their attention. There are many reasons why an animal may communicate in this way known as “multimodal signaling”– they may be able to transmit more information or use multiple signal forms to get across the same message to a receiver, among other theories. However, we know much less about the receiver side of communication, in particular whether receiving a signal in one form may influence the ability to receive the signal in another form.
Researchers Kelly Ronald and colleagues addressed this by performing a study on brown-headed cowbirds (Molothrus ater). When trying to attract females, male cowbirds perform an elaborate visual display of wing-spreading and puffing combined with a song, meaning that their courting signal is multimodal in nature. The female uses this display as an indicator of male quality and it influences her eventual mating decision. The researchers in this study were trying to provide some preliminary evidence for whether the receiver’s signal processing capabilities are influenced by one signal modality over the other. Essentially, they studied whether female cowbirds are sensory ‘specialists,’ meaning processing of one modality affects the processing of the other, or ‘generalists,’ where information can be processed well between both modalities and thus the ability may vary within a population.
The researchers tested female cowbird auditory and temporal resolution, or environmentally, the ability to detect changes in wing movement and song, to determine whether there is a positive correlation between the two. A positive correlation would mean that the signals increase each other’s filtering capacities and thus the female makes a decision about the male best when receiving a multimodal signal. Using electrodes that can measure brain response to sound, the researchers were able to equate how well the female cowbirds can resolve sound. They then determined auditory resolution by measuring eye responses to light pulses. The two resolutions were statistically compared to determine the correlation.
The results of the experiment did in fact reveal a positive correlation between the female cowbird’s ability to resolve auditory and visual information, and this study provides some of the first evidence of their association. Female cowbirds are thus sensory ‘generalists,’ so those that can resolve the male’s visual display well also resolve the auditory mode of it well. This aids them in both discriminating among males and determining which ones are of the best quality for mating. This holds implications not only for how multimodal signals interact on the receiver’s end, but also for the evolution of male signals that are preferential to females. If females prefer males with multimodal signals, then this may have driven the evolution of those signals. Who is to say that this couldn’t exist among other animals?
Ronald, K.L., Sesterhenn, T.M., Fernandex-Juricic, E., & Lucas, J.R. (2017). The sensory substrate of multimodal communication in brown‐headed cowbirds: are females sensory ‘specialists’ or ‘generalists’? Journal of Comparative Physiology A 203: 935-943.