Cultural Breakdown of Learned Avian Alarm Calls: Implications to Management and Conservation

Abstract

Mobbing is a common response of prey birds to aggressively displace potential predatory birds. This behavior transcends lineages and empirical evidence indicates that auditory cues from one species elicit mobbing responses in the same and/or different species. The black-capped chickadee (Pocile atricapillus) varies the number and length of D notes in the chick-a-dee mobbing call to denote information about the threat level a potential predator poses, with more numerous, shorter D notes designating a high threat. However, their limited natal dispersal may result in restricted transmission of culturally important vocalizations, which are known to quickly diminish in songbird populations that become isolated or are small in size, potentially exacerbating their decline. Whereas the black-capped chickadee and associated mixed flock members are common, we use this system as a model to study the cultural transmission of information important to prey survivorship and as a model of cultural breakdown in bird populations that are threatened by isolation. This project was replicated in areas containing persistent populations of Eastern screech owls (Megascops asio) and in those historically lacking them to assess whether black-capped chickadee alarm calls have a site-specific learned cultural component. Regional dialects are not hard-wired but learned in many songbirds, and locale-specific calls may uniquely convey information to members of the same mixed flock. Our data show that chick-a-dee warning calls differ in response to eastern screech owl presence. Where black-capped chickadees co-occurred with eastern screech owls, the average number of D notes was 5.25 but in areas lacking them, the average number of D notes was 2.25. Moreover, the length of the first D note was 40% shorter in areas with a persistent screech owl population. This indicates a breakdown in their vocal culture and suggests management that increases the connectivity of otherwise isolated populations can be of strong conservation value to many son