Research

Here are three of the main programs of research being carried out in our lab:

The Social Complexity Hypothesis for Communication

Many animal species are social. Species, and populations within species, vary in the complexity of their social groups. For example, some groups are larger than others, and some exhibit fission-fusion dynamics whereas others are stable in composition over time. Might the complexity of social groups influence the complexity of their communicative signals? This argument is called the ‘social complexity hypothesis for communication’, and is described in a recent publication: Freeberg, Dunbar, & Ord (2012). We received funding from the National Science Foundation to carry out field and captive studies to test this question – collaborators on the project include Drs. Katie Sieving from the University of Florida and Jeff Lucas from Purdue University, and their students.

Our lab has tested the social complexity hypothesis for communication experimentally, using Carolina chickadees, a common songbird species in the southeastern United States. We found that larger flocks of Carolina chickadees in the field used chick-a-dee calls with greater complexity (higher uncertainty) than smaller flocks of chickadees. Furthermore, chickadees experimentally placed into larger aviary flocks used chick-a-dee calls that were more structurally complex than did chickadees placed into smaller aviary flocks.

Functions of Variation in the Chick-a-dee Call

A key signal used by individuals of parid species (the titmice, tits, and chickadees) is the chick-a-dee call. In most species, the call is used by both sexes throughout the season, and functions in social cohesion. The call is structurally complex, being made up of distinct note types that follow note ordering rules for call construction. We have described some of the structural complexity of the call in different publications (see Publications link). How does that structural complexity relate to function? In other words, is variation in how the calls are produced associated with variation in signaler context and in receiver behavior?

Our lab has been assessing the function of variation in the chick-a-dee call using naturalistic observation and experimental manipulation studies of Carolina chickadees and tufted titmice. As observed in studies from other labs, many conducted with other species, we know that birds produce more calls and more ‘D’ (sometimes referred to as ‘dee’) notes in their calls the greater the risk. For example, birds produce more calls and tend to produce more D notes when they detect a dangerous predator that is closer to them compared to farther away from them (Bartmess-LeVasseur et al. 2010 Behav Ecol Sociobiol). Chickadees also produce more D notes in their calls when they first detect a new food source, and such calls may function in recruiting flock mates to the location of the signaler (Mahurin & Freeberg 2009 Behav Ecol). Chickadees produce more ‘A’ notes in their calls when they detect a potential flying threat near them, such as a predatory hawk (Zachau & Freeberg 2012 Behav Ecol Sociobiol). Finally, chickadees produce more ‘C’ notes in their calls when they are in the context of flight compared to when they are perched (Freeberg & Mahurin 2012 Ethology). Variation in note composition and how that variation relates to possible functions is illustrated by the following figure, taken from the review article in American Scientist by Freeberg et al. (2012).

Chickadee and Titmouse Sensitivity to Predator Head Orientation

We have long known that individuals of prey species are sensitive to the presence of predators in the environment. In chickadees, tits, and titmice, for example, foraging and calling behavior change dramatically when a predator is detected. But not all detected predators are actively hunting or an immediate threat, so individuals of prey species might be sensitive to predator behavior and predator cues associated with risk. Some key cues we have studied are a predator’s body orientation (where the predator might be moving) and a predator’s head orientation (where a predator might be looking).

In our earliest studies of predator-risk-sensitive behavior to predator head and body orientation, we found that chickadees and titmice avoided feeders more and called more when a potential predator was oriented toward the feeder, compared to when a potential predator was oriented away from the feeder. Potential predators in these studies included a mask-wearing human observer (Freeberg et al. 2014 Animal Cognition) and models of domestic cats (Book & Freeberg 2015 Animal Cognition and Freeberg et al. 2016 Ethology). In another study we independently manipulated head orientation and body orientation of perched avian predator models (hawks and owls), and found that chickadees and titmice avoided feeders more when the head, rather than the body, of the predator model was oriented toward the feeder (Kyle & Freeberg 2016 Journal of Comparative Psychology). A more recent field experiment indicates these small songbirds are especially sensitive to the presence of eyes in avian predators (Kyle 2020 Animal Cognition). Ongoing studies with a greater variety of predator models and with robotics are aimed to determine the particular predator cues that are especially salient to these small songbirds.