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Fussing over food: factors affecting the vocalizations American crows utter around food

Pendergraft, LomaJohn T., Marzluff, John M.
Animal behaviour 2019 v.150 pp. 39-57
Corvus brachyrhynchos, aggression, crows, predators, vocalization, windthrow
American crows, Corvus brachyrhynchos, often loudly vocalize when gathered around a food source. Because doing so would attract unwanted attention from predators and competitors, animals that have congregated around food are only expected to vocalize if the benefits (e.g. recruiting or announcing themselves to allies, deterring competitors, warning of danger, begging for a meal, appeasing a dominant) outweigh these costs. Here we demonstrate that wild crows change the quality of their calls depending on the amount of food present. The crows near a large food windfall gave shorter calls compared to their vocalizations in food's absence, and playback of these short calls only prompted a mild aggressive response from listening crows. In contrast, the calls given before the appearance of food were longer, and their playback elicited behaviours from the listening crows associated with aggression and territory defence. These findings suggest that crows avoid giving territorial calls near an exploitable food resource and vocalize for other reasons. Taken together, this study provides insights on how the caller's current context can shift the costs and benefits of vocalizing.