Acoustic profiling in a complexly social species, the American crow: caws encode information on caller sex, identity, and behavioural context

Vocal complexity in a socially complex corvid: gradation, diversity and lack of common call repertoire in male rooks

Vocal communication is widespread in animals, with vocal repertoires of varying complexity. The social complexity hypothesis predicts that species may need high vocal complexity to deal with complex social organization (e.g. have a variety of different interindividual relations). We quantified the vocal complexity of two geographically distant captive colonies of rooks, a corvid species with complex social organization and cognitive performances, but understudied vocal abilities. We quantified the diversity and gradation of their repertoire, as well as the inter-individual similarity at the vocal unit level. We found that males produced call units with lower diversity and gradation than females, while song units did not differ between sexes. Surprisingly, while females produced highly similar call repertoires, even between colonies, each individual male produced almost completely different call repertoires from any other individual. These findings question the way male rooks communicate with their social partners. We suggest that each male may actively seek to remain vocally distinct, which could be an asset in their frequently changing social environment. We conclude that inter-individual similarity, an understudied aspect of vocal repertoires, should also be considered as a measure of vocal complexity.

American Crow Brain Activity in Response to Conspecific Vocalizations Changes When Food Is Present

Social interaction among animals can occur under many contexts, such as during foraging. Our knowledge of the regions within an avian brain associated with social interaction is limited to the regions activated by a single context or sensory modality. We used 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) to examine American crow (Corvus brachyrhynchos) brain activity in response to conditions associated with communal feeding. Using a paired approach, we exposed crows to either a visual stimulus (the sight of food), an audio stimulus (the sound of conspecifics vocalizing while foraging) or both audio/visual stimuli presented simultaneously and compared to their brain activity in response to a control stimulus (an empty stage). We found two regions, the nucleus taenia of the amygdala (TnA) and a medial portion of the caudal nidopallium, that showed increased activity in response to the multimodal combination of stimuli but not in response to either stimulus when presented unimodally. We also found significantly increased activity in the lateral septum and medially within the nidopallium in response to both the audio-only and the combined audio/visual stimuli. We did not find any differences in activation in response to the visual stimulus by itself. We discuss how these regions may be involved in the processing of multimodal stimuli in the context of social interaction.

Acoustic localization of crows in pre-roost aggregations

Crows are highly intelligent and social creatures. Each night during the non-breeding period, they gather on large pre-roost aggregations as they move towards their communal roost where they sleep. Crows make numerous and varied vocalizations on these pre-roost aggregations, but the purpose of these calls, and vocal communication in general, in these pre-roost aggregations is not fully understood. In this paper, an array of four microphones is used as a non-intrusive means to observe crow vocal behavior in pre-roost aggregations in the absence of human observers. By passively localizing animal vocalizations, the location of individuals can be monitored while simultaneously recording the acoustic structure and organization of their calls. Simulations and experiment are undertaken to study the performance of two time difference of arrival-based methods (hyperbolic location estimator and maximum likelihood estimator) for call localization. The effect of signal-to-noise ratio and uncertainty in measurement on the localization error is presented. By describing, modeling, and testing these techniques in this innovative context, the authors hope that researchers will employ the authors' approaches in future empirical studies to more fully understand crow vocal behavior.

Volitional control of vocalizations in corvid songbirds

Songbirds are renowned for their acoustically elaborate songs. However, it is unclear whether songbirds can cognitively control their vocal output. Here, we show that crows, songbirds of the corvid family, can be trained to exert control over their vocalizations. In a detection task, three male carrion crows rapidly learned to emit vocalizations in response to a visual cue with no inherent meaning (go trials) and to withhold vocalizations in response to another cue (catch trials). Two of these crows were then trained on a go/nogo task, with the cue colors reversed, in addition to being rewarded for withholding vocalizations to yet another cue (nogo trials). Vocalizations in response to the detection of the go cue were temporally precise and highly reliable in all three crows. Crows also quickly learned to withhold vocal output in nogo trials, showing that vocalizations were not produced by an anticipation of a food reward in correct trials. The results demonstrate that corvids can volitionally control the release and onset of their vocalizations, suggesting that songbird vocalizations are under cognitive control and can be decoupled from affective states.

Songbirds are renowned for their acoustically elaborate songs, but it is unclear whether they have cognitive control over their vocal output. Using operant conditioning, this study shows that carrion crows, songbirds of the corvid family, can exert control over their vocalizations.