Singing in the Brain

The ZENK gene soon led the researchers to discover another nucleus in the songbird vocal system, bringing the total to seven. With ZENK they were also able to define more clearly the roles of the anterior and posterior pathways. The anterior pathway (which, they knew, needed to be intact for learning to occur) showed signs of activity only when the birds heard songs by members of their own species. And after they had heard the song a number of times, the ZENK response began to fade. "With ZENK," says Jarvis "we now had a technique that essentially lit up the learning center."

Jarvis and Mello went on to look at budgerigars' brains. "The brains were much more similar to songbirds' brains than people thought," says Jarvis, "We found many of the same structures, and their placement in the brain was identical." One question remained: Did hummingbirds, too, have the brain structures and pathways necessary for learning?

To answer that question, Mello and his colleagues have made several trips to his native Brazil, to an area with one of the world's highest densities and species diversity of hummingbirds. The researchers set up a hummingbird feeder on the veranda of the Museu de Biologia Mello Leitao, a small museum and biological research station on the outskirts of the town of Santa Teresa, nestled high in the Atlantic tropical forest of Brazil's east coast. Part of the research involved learning to identify individual birds--no easy feat.

For the uninitiated, it is difficult to tell apart the thirty or so species of bejia-flores (Portuguese for "flower-kissers," the creatures we call hummingbirds) that live in this swath of forest, and it is mind-numbing to try following the activity of individual birds. They move so fast that keeping your eye on one is like trying to follow a single bee in a swarm. Banding--the field technique commonly used for telling birds apart--doesn't work: hummingbirds' legs are so tiny that there is little space for a band, and the birds weigh so little that attaching a band could significantly affect their ability to fly.

"After a couple of days, you start to see individual variation, a messy feather here, or a slightly darker color," says Linda Wilbrecht, a graduate student at Rockefeller. Working at Mello's field site in Brazil, Wilbrecht and her fellow graduate student Sidarta Ribeiro observed the behavior of individuals of two species, sombre hummingbirds (Aphantochroa cirrhochloris) and rufous-breasted hermits (Glaucis hirsuta). Wilbrecht and Ribeiro followed birds that were doing one of three things: singing in territorial defense, listening to recorded songs of conspecific birds, or perching quietly. These species were chosen, in part, because their songs are very different. G. hirsuta's is complex, while A. cirrhochloris's is fairly simple. A complex song is itself evidence that a bird learned its song: the innate vocalizations of birds (those produced by pigeons, for example) tend to be simple, with few syllables and a narrow range of notes. Because of the differences between the two species, Jarvis and Mello reasoned, one might be a learner and the other not--a possibility that would make their results quite intriguing.