Northern Harrier Circus cyaneus Linnaeus       Field Guide IDs: NG-106; G-70; PE-152; PW-pl 16; AE-pl 309; AW-pl 317; AM(I)-224 Nest Location Nest Type Eggs & Mating System Dev. & Parental Care Primary & 2ndary Diet.. Foraging Strategy F I: 31-32 DAYS SEMIALTRICIAL 1 SHRUB < 5 feet F -M 5 (4-9) MONOG (POLYGYN) F: 30-35 DAYS MF SMALL VERTS BREEDING: Prairie, savanna, slough, wet meadow, marsh. 1 brood. DISPLAYS: Courting male performs series of dives from near stall, including barrel-rolls in multiple U-shaped loops. NEST: Flimsy; on slightly elevated ground or in thick veg; of sticks, grass, etc., loosely lined with fine materials. EGGS: Bluish-white, usu unmarked, but 10% spotted with browns. 1.8" (47 mm). DIET: Esp voles, also birds, snakes, frogs, insects (esp grasshoppers), carrion. CONSERVATION: Winters s to n Colombia, n Venezuela, and Barbados. Blue List 1972-86; declining from loss of habitat and effects of pesticides: 20% of eggs showed shell thinning in 1970. NOTES: Like owls, has curved, sound-reflecting facial ruff which, with characteristic low (<7') flight, enables location of prey by sound. In 25 year WI study, 25% of nests were associated with polygynous matings, often involving subadult females; increased incidence of polygyny associated with high vole populations. Female feeds and broods young. Females aggressively exclude males from preferred feeding areas in nonbreeding season. Outside of breeding season, roost communally on ground. Formerly known as Marsh Hawk; known as Hen Harrier in Europe. STANFORD. NOTES: ESSAYS: Blue List; Eye Color; Raptor Hunting; Polygyny; DDT; Size and Sex in Raptors REFERENCES: Brown and Amadon, 1968; Hamerstrom et al., 1985; Rice, 1982; Temeles, 1986.