Birds
Harrier
Circus · also called harriers
A harrier hunts almost the opposite way a falcon does: instead of a fast, direct strike from above, it drifts low and slow over open marsh and grassland, wings tilted in a shallow V, listening for prey through an owl-like disc of feathers around its face. When it finally drops, it is often reacting to a sound in the grass it could never have actually seen.
Overview
Harriers, genus Circus, are slim, long-winged hawks found over open grassland, moorland, and wetland on every continent except Antarctica. They hunt small mammals, birds, and large insects using a slow, low quartering flight, aided by a shallow facial disc that helps them detect prey by sound.
A hawk built like an owl, nesting like neither
Male and female harriers often look strikingly different — pale grey males, streaky brown females — and unlike most hawks, harriers nest directly on the ground in dense marsh vegetation. Courtship includes a dramatic aerial food pass, the female flipping upside down mid-flight to catch prey from the male.
Status
Least Concern overall, though some populations are decreasing as wetland and grassland habitat is drained or converted, leaving exposed ground nests more vulnerable to disturbance and predation.
Harrier: common questions
Why does a harrier's face look a bit like an owl's?
Harriers have evolved a shallow facial disc, a ring of stiffened feathers around each eye that functions much like the more pronounced facial disc of an owl, helping to collect and direct faint sounds toward the ears. This adaptation supports a hunting style based heavily on detecting small, often hidden prey such as voles by sound as much as by sight while flying low over dense grass or reeds where visual detection alone would often fail.
What is a harrier's hunting flight actually called?
The characteristic low, slow, back-and-forth flight harriers use while searching for prey over open ground is called quartering, in which the bird works a stretch of grassland or marsh systematically with wings held in a shallow, tilting V-shape, watching and listening intently below. This energy-efficient search pattern allows a harrier to cover considerable ground while staying alert enough to drop suddenly onto anything it detects moving or making a sound in the vegetation.
Why do male and female harriers look so different?
In several harrier species, the male develops distinctly pale grey plumage with black wingtips, while the female and young birds remain a streaky, camouflaged brown throughout their lives, a striking level of difference between the sexes. This difference is thought to relate partly to different roles during breeding, with the more visible male performing conspicuous aerial courtship displays while the female's cryptic colouring helps her stay hidden while incubating eggs on an exposed ground nest.
Why do harriers nest on the ground instead of in trees?
Harriers hunt primarily over open marsh, moorland, and grassland habitats that often have few or no suitable trees nearby, so nesting directly in dense ground vegetation close to their hunting grounds is a practical adaptation to the open landscapes they occupy. This ground-nesting habit does come with real costs, since eggs and chicks are more exposed to mammalian predators, flooding, and disturbance from agricultural activity such as mowing or livestock grazing than nests built safely above ground in trees.