A pair of noisy ospreys - or fish eagles -- have built a nest on an electrical transfer tower at the entrance to Oaks Amusement Park. The graceful raptors with impressive wing spans built their large stick nest at the top of the tower, located near the private gate at the southern end of The Oaks. The noisy birds soar above the Willamette River and Oaks Bottom Wildlife refuge, where they find plenty of fish--their exclusive diet. Other local osprey nests are sited on towers near the old Southgate Theater and along the Springwater Corridor in Brooklyn and Sellwood.
Surprisingly, a pair of Cooper's hawks are also nesting in the same tower, about halfway down. Since the two species feed on different types of prey, there should be no competition for food, although it is unusual to see two such nests in the same structure. Passersby are watching the avian scene with considerable interest. While the Cooper's hawks are smaller birds, the larger brown and white ospreys are sometimes mistaken for juvenile bald eagles.
Brooklyn naturalist Jim Lints, a lifelong birdwatcher, explains the difference: 'Adult bald eagles, which nest on Ross Island, have distinctive white heads and wider wings for soaring. Juvenile bald eagles, sometimes larger than the adults, take a year or two before their brown head feathers turn white.
'While bald eagles feed mostly on small mammals and reptiles, they can also catch fish by snagging them out of the water while flying over the surface. Hawks also prey on small mammals, reptiles and amphibians.
'Ospreys, on the other hand, are exclusive fish eaters. they have longer, more streamlined wingspans that allow them to dive into the water and then take off again with their prey. You can distinguish an osprey at rest by the distinctive brown cheek patches on its white head, and the irregular dappled brown patches on its breast. In flight, the osprey's wings are angled more aerodynamically, like those of a seagull, although the osprey's wingspan is much longer - up to 6 feet.'
Lints spotted the osprey and Cooper's hawk nests during an April trek through Oaks Bottom. 'I was also surprised to see a Canada goose sitting in an old osprey nest further north along the Springwater Corridor,' he added. 'Generally, geese nest on the ground, where their young learn to walk before they fly. Any goslings that hatch up high in the air would have a long drop if they didn't first learn how to fly."
Oaks Bottom Wildlife Refuge, on the Willamette River bank just west of Sellwood, Westmoreland, and Brooklyn, is a perennially rich resource for birdwatchers and other nature lovers.