Owl-faced and slim

By Bill Chaisson
Of a Feather
When a raptor swooped across the rural road in Danby, N.Y. earlier this month, I initially thought it was an accipiter, most likely a Cooper’s hawk. I saw the flash of the blue-gray back and the long, narrow banded tail. But it flew quite differently; it moved with a distinct fluidity compared to the fidgety mechanical-toy stroke-and-glide of the Cooper’s. Accipiters are designed to make their way rapidly through a forest canopy; they have short, rounded wings for maneuverability and speed. This bird’s wings were long and dapper, just like the tail, and as he flew away, the white patch on his rump flashed in the morning light.

It was a male northern harrier (Circus hudsonius), one of three New World species in a genus of 16 found in open country around the globe. It is one of the several members of the genus that shows distinct sexual dimorphism, with the females inevitably browner and bigger. Aptly named, the northern harrier breeds across the northern half of the United States and throughout Canada and Alaska, excepting the Arctic coast and northern Quebec. Although they live in grassland habitat, they steer clear of tundra.

The males are slate gray above and white below flecked with rufous. Females are brown above and white below streaked with brown, tend to be 12.5% larger than the males, and up to 50% heavier. In flight the males’ outermost primaries and trailing edges of his secondaries are tipped in black and the wing undersides pure white. The long tail is banded in both sexes, but gray and white in the male and brown and white in the female. From below the females’ wings are boldly patterned in brown and white.

I was excited to see the harrier—which I grew up calling a marsh hawk—because since moving away from central New York in 2016 I have seen a harrier only on Martha’s Vineyard. Much of the island is actually forested or covered with scrub oak, but there are large patches of grassland on the southern coastal area.

I was in the southwest corner of Chilmark doing a story about a controversial bridge to Squibnocket, a nearly-island connected to the main island by a barrier beach on the west and a broader causeway on the east, which was crossed by an access road. Both the beach and the causeway were increasingly frequently—due to sea level rise—washed out by storms that filled Squibnocket Pond, which then took its time draining back into the ocean. The proposed bridge would allow the water to pass under—and preserve marshland— as opposed to the existing rock-armored causeway, which regularly failed to keep the sea out and kept the salt pond water in. The whole of the quasi-island is flat and sandy and covered with grass and forbs, only occasionally dotted with oak trees. This is northern harrier habitat.

In a 2006 study in The Condor, Maiken Winter and others found that larger species of open-country birds, including the harrier, went elsewhere when woody vegetation covered more than 30% of the landscape. Harriers and other large open-country birds were willing to live in patches smaller than 100 acres. (Only the greater prairie chicken was sensitive to patch size and wasn’t found in any open area smaller than 350 acres.)

In the Winter et al. study, which was conducted in prairie locations in North Dakota and Minnesota, a grassland could not include any roads and any intrusion by trees or shrubs couldn’t be more than 65 feet wide or intrude across more than 75% of the open area. Throughout its range, the northern harrier avoids mowed areas and cropland.

Harriers hunt by cruising over their territory. A 1987 study from Ohio found that they have four methods of hunting: “(1) gliding: prolonged, nonstationary, non-powered flight; (2) transect flight: rather straight-line powered flight, with 30°) turns/min; (3) quartering: powered flight to and fro over short distances, with >5 sharp turns/min; and (4) border-following: powered flight within 5 m of land- or vegetation-type edges, e.g., fencerows.” Non-powered refers to a smooth-gliding form of flight that is beautiful to behold. It is occasionally interrupted by an up-swoop and a short hover. The bird may or may not drop down on prey from there.

A distinctive feature of the harrier’s face is its owl-like facial discs, which have the same function as they do in owls: to funnel sound toward their ears. They generally fly low—~15 feet above the ground—where they can listen for their prey as well as look for it. They also tend to be quite vocal while hunting, although there is no indication they are using echo-location.

Harriers eat mostly small mammals, but they are quite opportunistic —especially the males—and also eat birds and do not turn up their noses at reptiles or amphibians. Between 5 and 35% of their pounces are successful. They will pluck the birds where they catch them, but other prey is carried to a perch or back to the nest.

The male that we saw in Danby earlier in June had a mouse in its talons and was moving in a determined way, perhaps toward a nest. Eggs hatch between mid-June and early July in New England. The nest is built on the ground amid tall, dense vegetation in an open area. The materials are eclectic; any form of grass, forb, or woody twig can be incorporated to build a platform that is about 1.5 feet wide. On dry ground it may only be a few inches tall, but in marshy areas they are built up to a foot high to avoid being flooded out.

The northern harrier is rare in the Northeast. In New Hampshire it is found mostly in Coös County. It is declining in abundance and is a Species of Greatest Conservation Need (SGCN) in all of New England except Maine.

Bill Chaisson has been a birdwatcher for over 50 years. He lives and works in Wilmot.