by Grant Yang
The Northern Harrier, or Marsh Hawk, is a majestic raptor that can be found in brackish and freshwater marshes, prairies, estuaries, and savannas. The Northern Harrier commonly appears in upper North America, including at the Palo Alto Baylands, during the breeding season, and during the winters they are spotted in the middle U.S., from Kansas to Arizona, into Mexico.
The Northern Harrier has a rectangular white rump, a long-feathered tail, and a broad, round facial disk, giving it keener hearing than most other hawks as well as the ability to pinpoint sounds. An adult male is pale gray above and white below along its 17"-24" body, while the tip of its wings is black. The adult female, usually larger than the male, is brown above and streaked brown on the breast while the immature female's breast and wings are streaked cinnamon. Seen from far away, the Northern Harrier can be distinguished by its long, yellow, hairless legs. The Northern Harrier, with its 40"-54" wingspan, can be seen flying low over the ground, alternately flapping and gliding, holding its wings in a shallow V. The Northern Harriers' flight is characterized by its unsteady tilting and leaning at angles as it glides. It can reach speeds up to 38 km/h for males or 30 km/h for females and juveniles.
A variety of animals are prey for Northern Harriers, including rodents, other smaller birds, insects, reptiles and amphibians; however, harriers prefer to hunt voles. The male harrier must provide food for the offspring, so depending on the vole population, some males can provide for more than one mate. Harriers hunt by flying close to the ground and swooping down on its prey. However, if it is unsuccessful in catching the prey in its first attack it will seldom pursue its prey. Its nesting area and its mating habits are greatly affected by vole populations and it has been called "The hawk that is ruled by a mouse." Harriers' nests are on the ground near water making the nests vulnerable to flooding. Their nests are also prey to various mammals like raccoons, skunks, and foxes as well as being in danger of trampling by elk and cattle.
Harriers also have other food sources, one of which is stealing prey from enemy predators including Red-Tailed Hawks, Rough-Legged Hawks, Short-Eared Owls, Black-Shouldered Kites, and most of all passerines. Passerines include a large range of birds from hummingbirds to woodpeckers. Individually a passerine would be easy prey for a bird like the Northern Harrier, but a mob of passerines will attack and steal food from a Northern Harrier when it is carrying prey. According to the Academy of Natural Sciences, a Northern Harrier will lose 5-10% of prey captures as a consequence of food-stealing from larger raptors.
Northern Harriers demonstrate their fitness with aerial acrobatic talents during their courtship display. They soar high rather than gliding low, as usual, and they perform numerous nose dives and up to seventy deep U-shaped dives during a single display. The male ends its "sky dance" with chattering vocalizations, and if the female is attracted by the display it follows the male into its nest on the ground. The clutch size for Northern Harriers is three to nine bluish white eggs; however, after the 30-day incubation period only two to three fledglings will emerge. The male will supply the nesting mother with food by dropping prey in mid-air directly over or near the nest. When predators approach the nest, the mother will respond aggressively by uttering distress calls to its mate, but because some males are polygamous it cannot protect its entire harem.
Northern Harriers are highly territorial especially because their
life style is dependent on food availability, which is why they must
have a large area to hunt. Since 1992 Northern Harrier population was
relatively high due to an abundance of the vole population. Although
the Northern Harrier population is strong in California due to
conservation efforts, its population is dwindling in other states in
North America such as Minnesota. A lot of harrier territory is lost
due to agriculture, industrial development, and urban development.
Therefore, unless vast expanses of land, provided by areas like the
Palo Alto Baylands are preserved, the Northern Harrier may revert to
its status as a species of special concern, as it was in the 1970's.
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