When one becomes familiar with the habits of the birds of this group, watching them as they course backward and forward over marsh and meadow in quest of their prey, it is easy to appreciate the appropriateness of their common name of Harrier. They spend most of the time on the wing in a steady gliding flight, seldom flapping, and usually but a few feet above the surface. Although there are several genera, we shall have space for only the typical genus (Circus), which embraces some twenty species, and is of almost cosmopolitan distribution. They are birds of moderate size, none apparently exceeding twenty-four inches in length, and of slender form, with relatively long wings and tail, and rather weak legs and slender feet. The head is small and there is a ruff of small, soft feathers, more conspicuous in some species than in others, surrounding the face, as in the Owls. The bill is small and rather weak, while the claws are much curved and very sharp. They are especially remarkable for the great diversity in coloration in the plumage of the male and female, an unusual condition among birds of prey. Only a single species the Marsh Hawk (C. hudsonius) is found in North America. The adult male is light bluish gray or ashy above, with the upper tail-coverts white, the tail silvery gray barred with blackish, while the upper breast is pearl gray, and the lower breast and abdomen white, spotted with rufous. The mature female is fuscous above, with the head and neck streaked, and the wing-coverts spotted or margined with rufous; the upper tail-coverts are white and the tail barred with ashy and black or buff and black, while the lower parts are buff, widely streaked on the breast and narrowly streaked on the abdomen with fuscous or light umber. The young are similar to the female, but are darker above and more tawny below. The total length of this species is from nineteen and one half to about twenty-four inches, and it is easily recognized on the wing by the conspicuous white patch above the ‘base of the long tail.
The Marsh Hawk is undoubtedly one of the best: known of our birds of prey, since its breeding range covers practically the entire continent. ” It is a familiar sight,” says Beddire, ” to see a pair, ,and often several, of these birds skimming close to the ground, now along the borders of a meadow, or the shrubbery found close to the banks of small streams, and the tule-covered borders of fresh or salt marshes, actively engaged in search of their prey. Its flight is singularly easy and graceful. One moment it may be seen sailing or drifting along before a strong breeze without an apparent movement of its wings, in the next it may raise or lower itself or turn completely over, in undulating motions; dropping suddenly in the grass, or staying suspended in the air over some point which might be suited to the location of its intended quarry.” Its food consists largely of meadow mice, ground squirrels, frogs, grasshoppers, locusts, and large crickets, and to some extent of lizards, snakes, occasional ground-haunting birds, and young poultry, and when hard pressed it is said to feed on offal and carrion. It has been known to come at the sound of a gun and carry off the wounded or dead bird, but on the whole it is deserving of the most careful protection for its agency in the destruction of mice, ground squirrels, and injurious insects. Dr. A. K. Fisher, who examined the contents of 124 stomachs, reports that 7 contained poultry or game birds; 34, other birds; 57, mice; 22, other mammals; 7, reptiles; 2, frogs; 14, insects, while 8 were empty. As might be expected in a species enjoying such a wide range, the nesting season varies in the different parts of the country, beginning as early as April in Texas, and not until June in the fur countries. The nest is always made on the ground or close to it, and usually not far from water, as a marsh or prairie grown up with tall grass or bushes, being placed in a thick bunch of grass, on the top of a tussock, or occasionally on a low bush. It is usually a slight affair of grasses and a few sticks, and lined with similar material and sometimes a few feathers from the sitting bird. Both sexes assist in building the nest, and when it is completed the complement of eggs is added, these being from three or four to six, and sometimes as many as eight in number, dull white or pale bluish white and mostly unspotted.