Distress Calls in the Acorn Woodpecker

Acorn Woodpeckers live in extremely stable kin groups. Nonetheless, only 59.9% of birds caught in roosting aggregations gave distress calls or fear screams. Distress calling was highly repeatable among individuals and apparently heritable. However, the incidence of distress calling did not vary seasonally or according to age, sex, or status. Also, with two marginally significant exceptions, distress calls did not vary consistently with group characteristics or with the composition of roosting aggregations. Screams did not attract conspecifics, but sometimes attracted large mammalian predators. These results fail to support Rohwer's (1975) "calling for help" hypothesis and instead are consistent with Högstedt's (1983) "predator attraction" hypothesis that distress calls function to attract secondary predators that will distract or dispute the original predator, thereby inadvertently allowing the caller to escape.