Bald eagles seen along the Animas River corridor this time of year are probably homebodies, not the migrants that visit to escape the cold elsewhere and then leave, avian experts say.
The fact that eagles hang out here all year round is all the indication needed that the birds comeback is a success story. The species is so little a concern now that officials barely keep track of it.
On Sunday, celebrants will enjoy the 43rd annual Earth Day. When the event began in 1970, the bald eagles future was in question.
After DDT was banned in the 1970s, the bald eagle recovered enough to be upgraded from an endangered species to the threatened category in 1995. It was removed from the threatened list in 2007.
We still participate in bald eagle breeding and winter-population surveys, said David Klute, with Colorado Parks and Wildlife in Denver. But the population is doing so well, were putting less effort into surveys.
Susan Allerton with the Durango Bird Club said that because the river is free of ice, eagles can find fish, one of their major foods. But many move on when the season changes, she said.
If bald eagles are nesting here, they probably live here, Lynn Wickersham said. But many come here just for the winter.
Wickersham is compiling the second edition of the Colorado Breeding Bird Atlas which includes bald eagles through the San Juan Institute of Natural and Cultural Resources at Fort Lewis College.
The atlas is consulted for varying reasons by state and federal agencies, wildlife biologists, environmental consultants and land managers, she said.
The countys resident bald eagles apparently dont always produce young that fledge, biologists say.
Disturbances from humans or vehicles, a shortage of food or simply nonviable eggs can produce an empty nest.
In songbirds, Ive seen parents abandon the nest if there is not enough food, Wickersham said. But unless there is intense monitoring, its hard to say.
But there is good news. Overall, bald eagles are an environmental success story, biologists say.
The species was on the brink of extinction in the middle of the 1900s from sport hunting and the ingestion of the pesticide DDT found in their prey.
The pesticide weakened and cracked eggshells, compromising reproduction.
The species is now breeding in 48 states. There are none in Hawaii and one other state doesnt have a breeding eagle population.
Becky Gillette, the Southwest Colorado director for the Audubon Society, said a nest near Arboles has produced fledglings annually for three or four years.
I dont know if its the same pair bald eagles are monogamous but theyre there and they have one or two fledglings a year, Gillette said.
Eilene Lyon, a freelance field biologist in Durango, said its fascinating to watch nest interaction.
Eggs hatch two to three days apart, so the first-born has the advantage when its time to eat.
The most aggressive of chicks are the ones who grow, she said. Parents dont see that all chicks get fed.
Lyon works part-time as a stewardship monitor for the La Plata Open Space Conservancy, making sure conditions of easements are met. She also works as a field biologist for SWCA Environmental Inc.
In the winter of 2009-10, she was involved in monitoring a bald eagle nest along the Pine River near Ignacio for effects from a nearby Southern Ute Indian Tribe contruction project.
She spent February to May in 2009 monitoring a bald eagle nest along the Salt River in southern Arizona.
It was part of an unsuccessful Hopi Indian effort to get the regions bald eagle population listed as a subspecies because of its isolation and distinct characteristics.
Bald eagles hang out near rivers to drink and hunt fish, one of their favorite foods.
Theyre not all adept at catching fish, so theyre opportunistic, Lyon said. They steal food from other birds and eat carrion as well as hunt.
Bald eagles dont breed until theyre 5 years old. They dont get their white feathers, which signifies adulthood, until theyre 4 years old.
Kristi Streiffert, owner of For the Birds, which sells bird food and paraphernalia for bird lovers, sees bald eagles all year long in the Animas River corridor.
If we have a healthy river, well have a healthy bald eagle population, she said.