Males are pale gray above and white below, with black wing tips. Females are dark brown above and buffy below, with some streaking on the underparts. The immature Northern Harrier appears similar in color to the adult female, but has a cinnamon-colored breast and darker brown back and wings (Bent 1937, Brown and Amadon 1968). All show a distinctive white rump patch at the base of the tail, and have long, narrow wings and tail. Northern Harriers range in length from 17 to 23 inches, and have a wingspan of 38 to 48 inches. Females are larger than males.
MORPHOLOGY AND PLUMAGES: Members of the genus Circus
are slim, medium-sized hawks with long, broad wings and long legs and tails. A characteristic facial ruff gives them an owl-like appearance (Brown and Amadon 1968). The tail is barred. The mean weight of adult female is 529.9 grams (Hamerstrom 1986), total length varies from 48 to 61 centimeters and wingspread ranges from 110 to 137 centimeters (Bildstein 1988). The mean weight of the adult male is 367.4 grams (Hamerstrom 1986), total length ranges from 44 to 51 centimeters, and wingspread varies from 102 to 114 centimeters (Bildstein 1988). Males up to three to four years of age have brown markings dorsally (Bildstein 1988). Immature plumage is retained throughout the first winter into the following spring and, in some cases, summer. During spring and early summer it is difficult to discriminate between immatures and adult females (Bildstein 1988).
VOCALIZATIONS: The call given by adult and immature Northern Harriers when they are alarmed or excited has been described as a rapid chattering, "ke-ke-ke
", or "chek-ek-chek-ek
" (Brown and Amadon 1968). The begging call has been described as a wailing squeal, given by the female to the male, and juveniles to adults when begging for food. This call is also used during courtship by the male and female (Bent 1937, Brown and Amadon 1968, Balfour and MacDonald 1970, Watson 1977). When incubating the female may utter a "quip quip quip
" (Brown and Amadon 1968).
EGGS: Eggs are pale blue at laying and turn white in a few days; brown markings may occur (Hamerstrom 1969).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Swainson's Hawks have white on the tail feathers rather than the rump, and have shorter wings and tail. Osprey have a white head with brown eye stripes, and are rarely found more than a few miles from large rivers or lakes. Adults and immature Northern Harriers of both sexes have a distinctive, white rump patch.
Western Hemisphere Range
Most Northern Harriers depart for their wintering areas by late November, although some winter in Montana. Bozeman area normal migration periods: March 25 to May 5 and September 5 to October 20; peaks April 15 and September 20 (Skaar 1969).
Northern Harriers nest on the ground in dense grass, snowberry-rose patches, and hay fields. They hunt in grasslands, especially near wetlands and agricultural areas. Species occurs widely in valleys in open areas, generally not far from water. In late summer, some birds move upward into high mountain meadows (Skaar 1969, Davis 1961).
Small mammals, especially voles, form the majority of their diet. They also eat birds, amphibians, reptiles, and insects. Northern Harriers are the only hawks to use sound to locate prey, much like owls. Their hearing is much more acute than other hawks, although not as acute as owls.
A raptor census in 1944 showed this species comprising 18.5% of the total Montana hawk population (Davis 1961).
Northern Harriers arrive on their breeding areas in March and April. From three to nine eggs are laid in May. The eggs hatch in June and the young can fly at 30 to 35 days. Nesting starts in early May and continues into July (Davis 1961). Courtship in Bozeman area was observed between March 24 to May 3 (Skaar 1969). Young are on the wing in abundance in early August (Davis 1961).