The Northern Harrier

Despite the recent lack of rain, we are still entering into what is perhaps my favorite time of year to explore the grasslands and wetlands of California's Great Central Valley.  The weather is mild, and the end of winter is in sight.  Life rejoices!  Grasses are green, wildflowers are blooming, and new growth abounds in the tule beds.  And most importantly, bird activity is ramping up for the spring migration and breeding season.

If you venture out into one of our precious preserved open spaces this spring (use this tool to locate a National Wildlife Refuge near you), you are likely to come across a bird, medium in size and brown or gray in color, flying low, coursing back and forth across wetlands and adjacent fields and grasslands.  This marsh hunter is one of our most beautiful and unique diurnal raptors, the Northern Harrier (Circus hudsonius).

A female Northern Harrier, perched in the tules at Merced NWR 

Northern Harriers are among the only diurnal raptors to rely heavily on hearing, as well as sight, in search of prey.  Aided by their owl-like facial disks, which concentrate sound and funnel it to their ears, harriers fly low over their hunting grounds, head often angled characteristically down as they listen for small mammals, such as mice and voles.  Harriers will also take large insects, reptiles and amphibians, larger mammals, like rabbits, and birds up to the size of small ducks, which they often sit on in the water to drown.  (I once watched a female Northern Harrier spend ten or fifteen minutes sitting on a coot in several inches of water.)

While several species of harrier grace the skies across parts of Europe and Asia, North America has only one.  Listed in older field guides as the aptly-named Marsh Hawk, the common name was changed to Northern Harrier in the 1980's by the American Ornithological Union for the sake of continuity.  One of the goals of this organization is to make common names as appropriate and consistent as possible, and the "Marsh Hawk" was the only species of harrier worldwide that did not have the word harrier in its name, linking it to other closely related species.

As recently as 2018, another change came for the Northern Harrier.  Formerly considered a New World subspecies of Circus cyaneus, the Hen Harrier of Europe, our North American Circus cyaneus hudsonius at last earned recognition as a separate and distinct species, Circus hudsonius.  After extensive research, ornithologists have concluded that differences in DNA, vocalizations, size, plumage, breeding habitat and habits are significant enough to warrant the recognition of two separate species.  Luckily, this time the common name remained unchanged and few are probably aware of this recently discovered "new" species.

Notice the harrier's owl-like facial disk, feathers specially designed to capture and direct sound.

Nesting on the ground where they are concealed by vegetation, Northern Harriers breed throughout a variety of open habitats, from wetlands and meadows to tundra and prairies, across the Northern United States and Canada.  While they are winter visitors to the southern United States and Mexico, Central California has the privilege of hosting harriers year-round.  Common almost to the point of being ubiquitous in open habitat, including agricultural fields, grasslands, and both fresh and saltwater marshes, Northern Harriers are always a welcome sight.

In North America, where the Northern Harrier is our only harrier, separating it from other raptors in the field with just a glance is easy.  Its distinct flight style is unlikely to be confused with any other bird, and the obvious white rump patch it shows in flight is a dead giveaway.

While the plumage of female Northern Harries is colored in shades of warm brown, males are distinctively gray.  These "gray ghosts" are easily discerned from their female counterparts, and this sexual dimorphism is another feature unique among North America's diurnal raptors.

A glimpse of a "gray ghost," a male Northern Harrier cruising over wetlands at San Luis NWR.

There is one more reason I get excited every time I see a Northern Harrier: the presence of a harrier is indicative of suitable habitat for another of my favorite raptors, the mysterious Short-eared Owl.  Together, these two ghost-like hunters course low, gliding slowly over open habitat at dusk, a sort of changing of the guard as the diurnal Northern Harrier retires for the night and the crepuscular and nocturnal Short-eared Owl comes into its own.

An awe-inspiring scene: a diurnal Northern Harrier (on the left, with the white rump-patch) and nocturnal Short-eared Owl
share the sky at dusk.