April 30, 2014
Post by guest student blogger Maria Smith. Who knew that nuthatches could speak titmouse?! Thanks for a great post, Maria.
Small songbirds can exhibit quite complex vocal behavior, especially in the presence of predators. Researchers have found that some species modify their calls and their calling rates when facing danger. Julia Bartmess-LeVasseur and colleagues conducted an experiment on common feeder birds to determine how they respond to models of predators. The researchers put unique combinations of color bands on the legs of Carolina Chickadees and Tufted Titmice so that they could identify individuals and also observed some unbanded White-breasted Nuthatches during their study. In a series of trials, the researchers placed either a model Cooper’s Hawk, a predator of small birds, or a model Mourning Dove, which is harmless to the songbirds, near a bird feeder. They recorded vocalizations and noted how much each individual ate from the feeder during each trial.
Chickadees, titmice, and nuthatches responded to the Cooper’s Hawk model by visiting the feeder less and eating less than when the dove was present. They ate even fewer seeds when the hawk was placed closer to the feeder. The birds were threatened and wanted to avoid being vulnerable at the feeder in the open when the hawk was present. The three species differed in their alarm calling behavior, however. Both Carolina Chickadees and Tufted Titmice called more often and used calls that sounded different when they saw the hawk compared to the dove. White-breasted Nuthatches did not change their calls at all when they saw the threatening hawk.
These differing responses to a predator can be explained by the social structures of the three species. Carolina Chickadees and Tufted Titmice are nuclear species in mixed-species flocks, that is, they form the main social group around which satellite species, such as White-breasted Nuthatches and Downy Woodpeckers, forage. Chickadees and titmice might be at the centers of such flocks because of their very social nature—both species live in large, complex groups for most of the year. These social conditions might necessitate wide vocal repertoires because birds need to communicate with many individuals in many contexts. Therefore, chickadees and titmice would be expected to use specific, sophisticated alarm calls when spotting a predator.
White-breasted Nuthatches, however, usually live in pairs and often remain within sight of each other, so they rely less on vocal communication than chickadees and titmice do. Perhaps the less social White-breasted Nuthatch forages with chickadees and titmice because it relies on them to sound the alarm when a predator appears. Life is dangerous for little birds, so they use whatever strategies will work!
Bartmess-LeVasseur, J., Branch, C. L., Browning, S. A., Owens, J. L., & Freeberg, T. M. (2010). Predator stimuli and calling behavior of Carolina Chickadees (Poecile carolinensis), Tufted Titmice (Baeolophus bicolor), and White-breasted Nuthatches (Sitta carolinensis). Behavioral Ecology and Sociobiology 64:1187-1198.