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If backyard birds were actors on a movie set, tufted titmice would be extras. The cardinal and blue jay in their showy plumage would surely play the leads, unless upstaged by the starling and house sparrow, masters of in-your-face attitude. Those birds seize our attention while the small, gray, fast-moving titmouse seems always to be lost in the background.
But when it comes speaking up, Baeolophus bicolor is not shy. The tufted titmouse has a voice that demands to be heard, especially when a predator or other danger appears. Then titmice are quick to use their high-pitched vocalizations to scold and hector with fury.
Recently, researchers at the University of Tennessee at Knoxville studied the alarm calls made by Baeolophus bicolor to determine their function. Titmice tend to spend winter in mixed species flocks. Are the sharp rebukes meant to warn only fellow titmice that a predator is near? Or are the calls also a warning to other species in the group? Are the titmice prompting their flock companions to mob the predator? Are they hoping the distress call will attract a larger predator who preys on the smaller one? Or are the titmice using a protean defense system, that is, sending a variety of signals, or mixed messages, meant to confuse the predator and allow for escape?
Standing in for predators. the researchers trapped a number of titmice, approached the trap, picked up the birds in their hands -- a disagreeable sensation from the avian perspective -- and recorded the vocalizations. An analysis of the distress calls showed that titmice were probably using a protean defense (jamming the signals, as we humans do to enemy radar) and at the same time, calling for a mob of fellow titmice to come to their aid.
There is one sense, however, in which titmice might be sending warning calls meant specifically for us. Titmice do not migrate and for the past fifty years they have been moving north. There are a number of reasons for the northward shift, among them climate change. Considering that last year was the hottest recorded in U.S. history, shouldn't we be paying attention to Baeolophus bicolor?
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