By Sean Henahan, Access Excellence

When the young bald eagle is ready to leave the parental nest, instinct drives it north. Researchers at the Santa Cruz Predatory Bird Research Group (SCPBRG) have become the first to track immature bald eagles on their coming-of-age flights.The birds are fitted with lightweight satellite transmitters that send signals every ten days. Signals are beamed from the transmitter to a satellite, which relays location  information via e-mail to the researchers.

Data sent from the transmitter on a bird now being tracked showed that it flew some 900 miles in August from its nest at Lake Shasta, in northern California, to the vicinity of the Dean River in central British Columbia. The journey took less than three weeks. Subsequent signals showed that the bird is staying at the Dean River, apparently having found a rich source of food. Biologists think other young eagles may venture even further north, into northern British Columbia and southeastern Alaska's spectacular fjords.

"Instinct drives these migrations," said SCPBRG researcher Grainger Hunt, Ph.D. "These young birds have never hunted before and have never caught anything. Yet they leave their parents behind and suddenly, they fly a thousand miles north at the end of the summer. It's very surprising."

If all goes well, the researchers will get a report on its location every 10 days for the next two years. The straps on the backpack containing the transmitter are designed to fail after that time. Over the next two years, if both eagle and satellite tag survive, the biologists will learn how long the bird remains in Canada and whether it returns to its home range for breeding. The research also paves the way for satellite tagging of more eagles, as well as falcons, seabirds, and other species of interest.

"Bald eagles are indicators of the health of the global ecosystem," Hunt said. "These telemetry studies will teach us about the eagles' food web. We may learn that the ecology of California bald eagles is tied to the health of the northern salmon runs, and thus to the abundance of plankton in the Pacific Ocean."

Hunt speculates that juvenile bald eagles start by eating carrion along the mouths and inland stretches of big rivers with huge salmon die-offs. Later, they learn how to catch live fish--a necessity before they reach breeding age.

The satellite technology represents a major improvement on previous attempts to track the eagles with radio telemetry. Researchers had attempted to follow the flights of young bald eagles northward by plane in the mid-1980s, but usually lost track of them in bad weather.

"This is a completely different kind of wildlife biology, like going from a typewriter to a word processor," said Brian Walton, longtime SCPBRG coordinator. "This technology will be important for tracking seabirds, which we can't follow by plane." Such birds, Walton noted, could include birds injured in oil spills, then cleaned and released. Satellite tags present a new way to gauge the effectiveness of those techniques.

SCPBRG researchers use Geographic Information Systems technology to map the bird's movements. The project is part of the group's overall management efforts for birds of prey, including the peregrine falcon in California. SCPBRG is credited with restoring the peregrine falcon to healthy breeding levels in the state throughout the 1970s and 1980s.