After a long winter of snow and stillness, the sounds of bird life are returning. From the honking of geese overhead to the "conk-la-ree" of the red-winged blackbird, in the coming months, the music of our avian neighbors will fill the air. Their calls are more than just a harbinger to the warm weather ahead, they are rich with information.
Walk through the woods with a birder, and the sounds of the forest take on new meaning. Trills and whistles now have a distinct source, even if the bird that made them remains hidden in the canopy. As bird songs become more familiar, you realize the world of these social creatures is bustling. In the spring, many birds have recently arrived after migrating from a warmer location. Now, finding a mate and building a nest are two of their most pressing tasks.
During the spring and summer, Dr. Ken Schmidt, an avian behavioral ecologist from Texas Tech University, investigates bird life on the Cary Institute's 2,000-acre campus. Through funding from the National Science Foundation, Schmidt and his research team are studying how ground-nesting songbirds choose their breeding territories and nest locations. They are specifically testing whether songbirds eavesdrop on their forest neighbors when making these crucial decisions.
The study's focal birds are the veery, a forest thrush that has a beautiful and complex song, which sounds like a marble whirling down a metal tube; the ovenbird, famously known for its "Dutch oven" like nest (because of its side opening as opposed to the more traditional cup-shaped nests) and the worm-eating warbler, whose tiny nests are often hidden on steep forest floor slopes.
A nest's location is significant because it is the bird's first defense against nest-robbing predators. A safe location helps ensure the survival of offspring. To reveal the factors influencing nest choice, Schmidt alters the soundscape of the forest.
A soundscape is an auditory version of a landscape, defined by sound rather than habitat, slope, and terrain. Step outside your front door. You are bombarded with the sounds of the door shutting, an engine engaging down the street, a dog barking. These sounds inform you about your neighborhood — Mr. Smith is off to work; Spot, the neighbor's terrier, is out in the yard.
In the forest, songbirds also rely on the informative sounds of their neighbors. And from these sounds, they can determine threats in the environment.
Schmidt's study is testing two specific sounds, the "peter-peter-peter" of the tufted titmouse and the chips and chucks of the eastern chipmunk. The tufted titmouse represents positive information — it is notorious for vocalizing when a predator is near. Nesting near a titmouse is akin to having a predator alarm system.
Chipmunks, on the other hand, represent negative information. They are voracious consumers of bird eggs and nestlings.
By broadcasting these sounds in different areas of the forest, Schmidt is testing if birds will nest near the positive sounds of a good neighbor and away from the negative sounds of predators — implying that they use and benefit from eavesdropping behavior.
Calls will be played this spring; by mid-May, Schmidt's field crew will be busy searching the forests for the location and status of bird nests. Nests reveal the end product of a complicated decision the bird has made. Changes in nest location would be a strong indicator that birds are listening to their neighbors and changing their behavior as a consequence.
Hannah Liddy spent the summer of 2010 working with Ken Schmidt's research team. Ken Schmidt is a Visiting Scientist at the Cary Institute.