Talking about food: Form and function of food-associated calls of the American crow (Corvus brachyrhynchos)

摘要

Cooperatively breeding American Crows (Corvus brachyrhynchos ) ("crows") give food-associated calls in two contexts: when food is discovered on territory; and by females beginning incubation when family will feed them on the nest. Both calls reveal the caller's location to both conspecifics and predators. An assessment of the information in these calls is essential to understanding the benefits to the caller and family members. In a well-studied, suburban population of American crows in Ithaca, NY, I assessed the acoustic characteristics, individual distinctiveness, context and function(s) of nest calls. I also characterized the food-associated "chevron"-shaped caw, comparing it acoustically to the similar inflected alarm caw.;Breeding female crows give loud, begging-like "nest calls" from their nests during egg laying and early incubation. These may elicit feeding by their family group, but could advertise the callers' fertility. I found that a female's nest calls were acoustically individually distinctive. Distinctiveness did not vary with distance between nesting females overall, but nearer females were more similar in the one year following West Nile Virus and potentially shorter dispersal distances for young females. Female crows began to give nest calls within a few days of the start of incubation, when they were still fertile. Thus, nest calls do identify non-mate fertile females. The few observed extra-pair copulation attempts were strongly resisted by females, leaving it unclear if advertising location and fertility is costly to callers. Females gave nest calls at a higher rate in the mornings after days with below freezing minimum temperatures, evidence that the calls signals real nutritional need.;American crows are among those social species that produce food-associated calls when encountering food. Calling individuals may bring competitors, but eat more safely and share cooperatively with group members. The food-associated calls of American crows had not been characterized as a distinct call. In comparing the crows' similar inflected alarm caw to the food-associated caw, I demonstrated that, like the alarm caw, food calls differed among individuals. Unlike alarm calls, they did not differ with sex of caller. I found that the food-associated "chevron"-shaped caw may not be food-specific and may indicate general alarm.