High Country Birding: Osprey have made a comeback in Summit County
August 18, 2014
Twenty percent of Summit County's 600 square miles is water: High Country lakes, reservoirs, rivers and creeks. Combine this with an abundance of fish and eye-boggling scenery, and it's easy to see why the county attracts fishers from around the globe. However, wader-wearing visitors aren't the only anglers showing up in the summer. The osprey, a 4-pound bird with a 6-foot wingspan and an insatiable appetite for fish, is competing for those blue-ribbon trout and doing quite well at it.
Once seriously threatened, osprey staged an enormously successful comeback and can now be found across the world on every continent except Antarctica. Our Summit County birds are among the highest-elevation nesting osprey in the world, with nests at 9,100-foot Dillon Reservoir and along the Blue River, as well as near other fish-rich waters.
It's been a tough road for osprey. Hunted for sport, shot as vermin and crowded out of native habitat, their biggest challenge came with the widespread use of DDT in the 1950s and '60s. DDT accumulated in the cells of water life from plankton upward, building higher concentrations as it moved up the food chain, and its metabolite, DDE, impeded ospreys' ability to produce sufficient calcium for eggshells. Attempting to incubate these calcium-shy eggs, mother ospreys inadvertently crushed them.
Fortunately, for ospreys and other birds, a ban on the use of DDT in the U.S. in 1972 reversed this decline. The loss of habitat and suitable nesting sites also have been mitigated by the widespread construction of artificial nesting poles, many of which can be found in Summit County. Ospreys also easily adapt to human neighbors, and they don't hesitate to nest near urban activity.
Western Hemisphere ospreys nest as far north as Canada and Alaska. Those along North America's East Coast winter as far south as Brazil and beyond, though western ospreys rarely winter further south than Mexico and Central America. The Rocky Mountain Bird Observatory attached tracking devices to two ospreys in June last year and shares the movement of these two birds with the public on its website. You can track them at http://www.rmbo.org.
The two females, Shadow and Rainbow, left their nests last fall, flew east to central Kansas, turned south and took a straight-line route through Texas to sites just across the border in Mexico. Interestingly, even though they were adult nesting birds in 2013, they stayed in Mexico this summer, rather than returning to Colorado to nest. Juveniles remain on the wintering grounds through at least one summer, but adults generally return to nest again.
You can easily find osprey nests in Summit County, both at the Frisco Bay Marina and along the Blue River north of Silverthorne. The nests are huge platforms of thick sticks, resting high on tall nesting poles. The one just north of Golden Eagle Drive is enormous, with annual additions since at least 1995.
Ospreys generally are monogamous, sometimes bonding for life, which can be as long as 25 years. They typically hatch two to three eggs, though the first-hatched bird dominates the others and survival expectancy for a third hatchling is slim. Incubation and fledging are prolonged, taking as long as two months. During this time, the male adult hunts incessantly, feeding the entire family and typically fishing within 10 miles of the nest.
Osprey have a unique talon arrangement, allowing them, once airborne, to reposition the fish face-forward, giving the bird an aerodynamic flying advantage. They spot prey from on high, plunging talons-first into shallow water to snag fish. Their strong wings allow them to lift fish weighing as much as half their own body weight, though they have been known to drown trying to land a lunker. Just like with humans, going for bragging rights can be risky.
Bob Bowers is a naturalist and freelance writer specializing in nature and travel articles. He writes a monthly birding column for an Arizona newspaper, lives in the mountain foothills near Tucson and spends much of his summer in Keystone. He writes a birding and travel blog, http://www.birdingthebrookeandbeyond.com, and his email is firstname.lastname@example.org.