By Bill Chaisson
Since discovering it a couple weeks ago, I have started visiting a broad-winged hawk nest as often I can. Initially, I thought there were three eyasses, but now I think there are two with one parent often sitting very nearby on a horizontal branch. According to John Blakeman of the Franklin Institute Hawk Watch in Ohio, “eyass” is the falconry term for young hawks and eagles. They keep that name through the summer, even after they fledge. When they are ready to migrate in mid September, they become “passagers.”
According to the “Atlas of Breeding Birds of New Hampshire,” broad-winged hawks lay their eggs when deciduous trees first begin to leaf out, which around here is about the middle of May. The female incubates the eggs for about a month. By about their fifth week of life, the young hawks start to move out of the nest. These young Sutton hawks still have tufts of down sticking out from odd places among their contour feathers, and I have not seen them outside the nest, so they are a little behind schedule.
The nest of the broad-winged hawk is unimpressive. In his Atlas article, Kimball C. Elkins notes that this species usually builds a new nest each year. Both the male and female construct the basic platform of twigs 25 to 40 feet up in a tree, and within it the female creates a bark-lined cup less than a foot wide. The Sutton nest is in a white pine (which is unusual; the species favors deciduous trees), perhaps 30 feet above the ground. It overlooks a recently logged opening in the forest and is perhaps 100 yards from a dirt road lined with seasonal homes.
In contrast, the bald eagle builds the largest nest of any North American bird. While the broad-winged nest is perhaps two feet across, an eagle nest can be eight feet wide. They also grow to be 12 or 13 deep because a pair will return to it year after year and add a new layer. Eagles live for decades and the aerie, as it is called, may eventually weigh over a ton.
The crow-sized broad-winged hawk spends most of its life hunting below the canopy, and it nests there too. Eagles hunt fish in open water and their nests are placed at the top of a mature tree or large snag, often one that sticks up above the rest of the canopy. A bird with a 8-foot wingspan needs room to take off and land.
While bald eagles usually place their aeries in large trees, they may also build them on cliffs. Golden eagles have the reverse preference, usually nesting on cliffs and occasionally in trees. Like those of bald eagles, the nests of golden eagles are huge, with the largest one on record being 20 feet tall and eight-and-a-half feet wide. Goldens apparently build with more varied materials, often incorporating man-made objects like fence posts and barbed wire. They also line the nest cup with aromatic leaves, perhaps to discourage insect pests.
Both eagle species may also choose a man-made structure as a nest site, but ospreys seem especially fond of them. On my last trip back to Ithaca, New York, I was startled to find a platform had been erected in Stewart Park, a much-frequented city property on Cayuga Lake. An osprey was quite happily nesting there above the picnickers.
When I worked in Vineyard Haven on Martha’s Vineyard, I watched a pair of ospreys attempt to build a nest on top of the dome over a telephone transmission antenna. One morning after a windy night I saw it had blown off, with only a few sticks remaining. Ospreys are also more inclined to nest on the ground, especially on islands.
“Fish hawks” are famously fond of putting a nest on the cross-trees of a utility pole. According to my father, in southeast Massachusetts in the late 1940s and ‘50s you were never out of sight of a nest as you drove down the road. The weight and decay of materials had the tendency to cause outages. So, today power companies in some places where ospreys are common will add an extra set of cross-trees above the lines.
Ospreys eat fish, not other birds, perhaps one reason why other bird species have been found raising their young in the lower reaches of an osprey nest while the raptor is actively doing the same up top. A short communication by Peter Ewins of the Canadian Wildlife Service in the Wilson Bulletin (vol. 106, no. 4; 1994) noted that in Michigan and adjacent Ontario he found common grackles, tree swallows, starlings, house sparrows using cavities or recesses in the actual nest. A northern flicker created a nest hole a tree trunk immediately below an osprey nest, and a barn swallow had built its nest on the same concrete building.
Canada geese begin nesting before ospreys do. According to Ewins, on several occasions they occupied osprey nests and had begun raising their young when the ospreys returned to begin their breeding season. In some cases the ospreys chose another site, but sometimes they simply laid their eggs elsewhere on the same large nest.
According to Ewins review of the literature, the benefit to the smaller birds may be the protection afforded by ospreys as they defend their nest sites from crows, other raptors and some mammals. The ospreys in turn may benefit when the smaller birds sound the alarm upon seeing predators that escape the attention of the raptor.
In addition to harvesting small feathers and down from ospreys to line their own nests, swallows also prey upon flying insects attracted to the rotting fish remains that dot the outer reaches of osprey nests.
Bill Chaisson, who has been a birdwatcher since age 11, is a former editor of the Eagle Times. He now works for the Town of Wilmot and lives in Sutton.