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Many bird and primate species produce specific vocalizations associated with encountering a food source. When the receiver of the call can predict events in the environment based on the call without external indicators the call is said to be functionally referential (Clay et. a1. 2012). For a call to be considered referential it must fit into two categories, production and perception (Macedonia & Evans 1993). To fit the production category the call needs to be specific for a certain stimulus or stimuli that all have a common feature, and the perception category requires that the receiver of the call responds according to the call's reference without any other indicators to the appropriate reaction (Macedonia & Evans 1993). The production category is studied using observations and the perception requirement is tested by playing back recorded calls and comparing the receiver's reaction to the original response.
Referential signals have features they share with human language, and this is a source of controversy (Evans 1997). Some researchers think there is no reason to compare the calls to language without evidence of a conscious decision on the animal's part (Evans & Evans 2007). The call may simply induce a motor reaction in the receiver and it only superficially resembles how human language works (Evans & Evans 2007). But if the call stimulates a mental depiction in the receiver 's mind of the event that caused the call, like a word it would represent something.
The avian family Paridae is a good group to examine functional reference because they have complex vocalizations and there is evidence for both referential alarm calls and referential food calls (Mahurin & Freeberg 2009, Sturdy et. a1. 2000, Templeton et. a1. 2005). The call focused on most in the literature is the complex chickadee call which has been found to have many different meanings depending on the variation and context of the call; the chick-a-dee call can be used as an alarm call that indicates predator size, a location call to indicate flying or perching, or a food call to recruit flock members to a new food source (Templeton et. al. 2005, Freeburg & Mahurin 2013, Ficken et. al. 1978).
In this paper, I will first review the literature concerning referential food calls, the calls in parids, the possible meanings for the chick-a-dee calls in chickadee species, and the application of optimal foraging theory to the wintering flocks in these species. Then, I will present the results of my study on the production of calls regarding food quality in wintering Black-capped Chickadees, Poecile atricapilla. I tested the hypotheses that Black-capped Chickadees (I) produce chick-a-dee calls when encountering a known food source and (2) vary the chick-adee call when recruiting f10ckmates to a food source to reflect differences in food quality. Finally, I will focus on how to modify future studies to answer questions posed by both the literature review and the preliminary experiment described here.
Gingerich, Josephine, "Food-associated calls in wintering Black-Capped Chickadees (Poecile atricapilla) and their possible meanings." (2014). Honors Theses. 2428.