RF transmitters can be good for small animals, particularly those that remain in small areas, and can work in areas of thick forest canopy or deep canyons that can block GPS signals. However, GPS is ideal for animals that range over large areas, and particularly those that migrate.
"With our satellite transmitters, you can track a bird or other animal anywhere in the world,” said Blake Henke, managing partner of North Star Science and Technology, a GPS tracking device company in Virginia.
Currently, GPS devices are not small or light enough to be placed on small birds, Henke said. The rule of thumb is that a transmitter, with its standard four-point "backpack” harness, should be no more than 3 percent to 5 percent of a bird’s weight. Currently, the lightest satellite transmitters weigh about 9 grams, so the smallest bird that could carry it comfortably would be about the size of a crow, Henke said. "Song birds, that’s the next great hurdle.”
Meanwhile, Sutton researchers hope to use GPS with some of the Sutton center’s Internet stars. "We are planning to put satellite transmitters on eagle chicks,” Wolfe said.
For several years, the center has hosted an "eagle cam,” a live continuous online video of an eagle couple raising their young at a nest near Stillwater. The last eaglet raised there, dubbed "J.J.” by some cam fans, drew 5 million hits to the Web site. The center has submitted proposals for grants to equip future fledgling eagles with GPS devices. Just before the juveniles are ready to leave the nest, researchers plan to climb up and attach GPS transmitters.
Then maybe Sutton staff can answer questions such as the most common inquiry of last season: "Where did J.J. go when he left?”