The higher-frequency bands are "even more intriguing," Vyssotski says, "because they may reflect some cognitive process." These frequencies were most active at the beginning of the trip, when the birds were orienting themselves. He says that the activity may correlate with the process of finding their way, but further study will be needed to bear that out.

The study is "a wholly novel approach," says Dora Biro, a scientist at University of Oxford who has previously used GPS to understand how homing pigeon use landmarks when flying over familiar places. She says the data confirm a growing body of evidence that pigeons rely on visual cues in the landscape to get around. The use of EEG signatures to pinpoint areas of interest to the birds, she says, "opens up an entirely new observational window onto how birds in flight perceive, memorize, interpret, and utilize their visual environment." One important question, she says, is the role of familiarity in their brain activity. In this study, the birds were not released far enough away from home for the researchers to see how their brains responded to completely unfamiliar features.

György Buzsáki, a neuroscientist and EEG expert at Rutgers University, says that the EEG data "are quite striking and surprising, especially the large changes between navigation over sea and land." He adds that very little is known about EEG patterns in birds, so there is still a lot of work to be done in interpreting the signals. Future devices that take higher-resolution measurements--perhaps even detecting changes in single neurons--could help clarify what is happening in the birds' brains.

The device these researchers used, which they term a "neurologger," has been used in one other published study, which analyzed sleep patterns in sloths and found that the animals don't sleep as much as their reputation suggests. Niels Rattenborg, a scientist at the Max Planck Institute for Ornithology who led the sloth study, is currently using the device to study sleep patterns of birds in the wild. "The vast majority of what we know about how the brain functions is derived from animals confined to the laboratory setting," Rattenborg explains. The neurologger, he says, makes it possible to bring the laboratory into the field, giving researchers a chance to investigate how animals use their brains on their own turf.