Described by Charles Darwin as having an “elegant and soaring flight” (7), the cinereous harrier is frequently encountered gliding over open habitats, scanning the ground for prey (5). It mainly feeds upon various mammal and bird species, including the downy chicks of coots and waders, but will also take reptiles, frogs and insects (5).
This species is normally silent, except during the breeding season, when the male and female make rapid, chattering calls while engaged in aerial, courtship displays and while defending the nest. Eggs are usually laid after mid-November, and the young are fledged by January. The nest is a heap of rushes, grass or other vegetation, up to 40 centimetres across and 30 centimetres deep, which is placed on the edge of bed of rushes or in damp grass or scrub (5).
The cinereous harrier is mainly sedentary, but populations from Patagonia migrate northwards between April and May, returning to the breeding grounds between September and October (5).