Food amount affects the vocalizations around and possibly recruitment to a food source by American crows

Abstract

While many non-human vertebrates share food, active recruitment to a food source is rare and limited to social species that benefit from having additional conspecifics at the food source. Here we demonstrate that wild American crows (Corvus brachyrhynchos) change the qualities of their calls around large food sources, but these changes did not appear to increase the number of crows present at the food bonanza. The crows near a large food windfall gave shorter calls compared to their vocalizations around a small amount of food (especially if they saw a human produce the food), and playback of those short calls did not prompt an aggressive response from listening crows. In contrast, the calls given before the appearance of food had a longer duration, and playback of those longer calls elicited behaviors from the listening crows associated with aggression and territory defense. These findings suggest that crows might be recruiting allies to food sources that are highly conspicuous, either from the large number of food items or from the visibility of the human source. Taken altogether, this study provides important insights into the importance that crows place on human behavior, possibly an adaptation from generations spent living in human-dominated landscapes.