However, there's still no such thing as free energy, and the real challenge will be to ensure the device serves its purpose without creating an unacceptable burden for the bird. Lots of similar efforts have failed for that very reason.
The Department of Defense, for instance, had hoped to create small piezoelectric devices that could convert a soldier's boots to electric generators to power all the gizmos that modern soldiers carry. It worked, but unfortunately, those boots had to keep on walking.
The Pentagon decided the soldiers spent more energy moving their feet than they got back from the device, and the program was abandoned.
The sensors used to monitor birds are very energy efficient, partly because of their simplicity. It's possible to determine a bird's latitude simply by knowing the length of the day, sunrise to sunset. The big energy drain is transmission of the data back to the scientists, but there are ways to limit that as well.
In less than a second a microcontroller can transmit an enormous amount of data, so it doesn't have to be on very often, Shafer said.
Farnsworth, the ornithologist, remains confident that these devices will soon be common, and very useful, especially when climate change could pose major problems for migrating birds.
Of course, birds plan their lives around seasonal climate change, moving from one area to another to take advantage of different resources. That's why many of them migrate.
But one huge question remains, according to Farnsworth. How quickly can they adapt to change on a global scale, and what can be done to help them? Maybe the answer lies in a backpack.