Friday, February 11, 2011

Marsh Hawk: Northern Harrier

A juvenile Northern Harrier tries to defend a fish carcass from an adult female. All images in this post by Doug Brown, except the final image.

Perched atop the limp body of a dead snow goose lying among the grasses in shallow water, the slim-bodied raptor yanked out yet another tuft of white feathers. The brown feathers that characterize female and young Northern Harriers stood in stark contrast to the brilliant white of her prey. Yank! More feathers flew! My friend asked how in the world this medium-sized raptor could have brought down an animal more than three times its own size. Yank! White down floated through the air. I explained about the opportunistic nature of all raptors, taking food that is easy versus fresh. Yank! White fluff surrounded the two birds. Perhaps the snow goose died of natural causes. Yank! I wondered if the diligently plucking hawk would ever reach the flesh of the goose. Yank, yank! Would a hungry Bald Eagle notice the growing pile of white that surrounded the brown? Surely, the harrier, weighing less than two pounds, would be no match for a predatory bird five times its size. Yank! We never knew the final outcome. Eventually, we tired of watching the slow motion drama, and moved on to another area, leaving the bird to her feast.

Not just vultures, known for their scavenging habits, but all raptors and almost all species of predatory animals are opportunistic feeders. Although hawks, eagles and falcons all take live prey, they also scavenge, steal from others and, in general, get food the easiest way possible. At crowded winter roosts, birds can easily spread disease, particularly among waterfowl that gather by the tens of thousands in a single pond. Avian cholera may very well have been the final straw for the goose that had flown south from its Arctic breeding grounds.

Adult male Northern Harrier.

Formerly known as the marsh hawk, the northern harrier hunts primarily on the wing and may cover up to 100 miles per day. Its normal prey, consisting mostly of rodents and small birds, is detected using extremely sharp hearing, facilitated by a pronounced facial disk that helps to direct sound toward its ears. Long yellow legs help it to snatch prey from tall marsh grasses. Commonly seen soaring low to the ground, coursing back and forth over marsh, field, or pastureland, the harrier holds its wings in a shallow “V”, also called a dihedral. The slender-bodied hawk has a long tail and wings, and a conspicuous white rump patch, making it one of the easier hawks to identify.

However, males and adult females are strikingly different. The males are a gorgeous shade of blue gray on their backs, white below with black wingtips, and lemon yellow eyes. Females and young of both sexes are similar with brownish backs, buff-colored undersides which are streaked in the adult females and solid in the juveniles. Males often tend to be found in more upland habitats, whereas females and young frequent lowland areas and marsh habitats.

Adult male Northern Harrier viewed from below.

The northern harrier is found worldwide. There are estimated to be more than 111,000 individuals in North America, breeding primarily in dense, tall marsh grasses, hence their common name, Marsh Hawk. The scientific name is Circus cyaneus which is derived from the the Greek words kirkos, meaning a circle, a reference to the bird flying in circles, and cyan, a blue color referring to the color of the male bird. Harrier is from the Old English word hergian, which means to harass, ravage, or plunder.

Harriers roost and nest on the ground, often in groups in a traditional location. Most males are mated to one or two females at the same time. Some males pair with up to five mates in a season. Females incubate the eggs and brood the offspring, while the male provides the bulk of the food for his mates and their nestlings.

Female or juvenile Northern Harrier, showing the prominent white rump patch.

Historic populations were considered abundant and widespread, but declines have been observed in recent decades. In 1972, this species was placed on the American Birds' Blue List and has remained there since. Declines were primarily due to a loss of breeding habitat and the effects of pesticides. Reforestation, filling in of wetlands, changes in land use, and urban and industrial development in coastal areas all contributed to habitat loss.

During the early-mid 1900s, rampant shooting of all raptors, then considered vermin, also contributed to declines. Attitudes changed and raptor persecution subsided, particularly for the littlish hawk known for dining on the small rodents so disliked by most humans. Subsidence; however, does not spell an end to raptor persecution, still practiced but relegated to shadowy corners.

Photo by Pete Jungman, a falconer in southern New Mexico.

It was 2009. I received a photo of a beautiful male harrier, shot dead; its lifeless body hung on a fence right next to a sign that said “no hunting”. A littlish raptor, minding its own business, helping to keep our rodent population in check.

No comments: