Here's a word for you: crepuscular.
Sounds slightly icky, but it actually describes something quite lovely: pertaining to dawn and dusk. In the animal world, it's used to describe species who are most active at first light and at twilight. That does not describe many hawks, who tend to do their work in the plain sunlight of mid-day. Today, I'd like to spend a few minutes with one who breaks with that pattern, the Northern Harrier.
Juvenile female Northern Harrier - click here for full size version.
There are just over a dozen species of harriers, and they are found on all continents except Antarctica. Only one species lives in North America, the Northern Harrier (Circus cyaneus), known as the Hen Harrier in Europe and Asia. They were also known as "Marsh Hawks", the name often seen in older field guides.
Harriers are ground nesters, and often nest in marshes to reduce predation problems. Unfortunately, they are running into problems in many areas as wetlands are drained. They probably gained hunting habitat as eastern forests were cleared for agriculture, but the open lands were not as good for breeding because nests could be destroyed by livestock, or if fields of hay are harvested. Though they are not considered endangered, their numbers have been in decline in many parts of the country.
Long wings and a long tail on a midweight body help them float over fields. (Don't worry - there is a hand holding the bird's body! It's just hard to see, it's from the guy with the green sleeves on the left.)
It's easy to identify harriers when they're hunting, as they have a very distinctive style, flying slow and low over open terrain (like marshes, grasslands and scrub). In fact, their genus name - Circus - refers to their habit of flying large circles over fields as they hunt. They also fly regular routes along ditches, hedgerows, fencelines and road margins. They take a wide variety of prey, including mice and other rodents, birds and herps. They have been known to take larger prey (like ducks and coots) by holding them down and drowning them.
The harrier's facial disc helps channel sound, much as an owl's does.
Harriers have several adaptations for their hunting style and for the hours that they keep. For their body size, they have long wings and a long tail, which makes them more bouyant and requires less flapping as they move over the land. Their long legs allow them to drop down on prey and grab it through the vegetation. Most distinctive of all is their owl-like facial disc - feathers arranged to channel sound to their ears so they can more easily locate prey by sound. It's interesting to go to an area with harriers and their nocturnal/crepuscular counterparts, the short-eared owls, and see how similar their hunting styles are.
This male harrier has not reached full adult plumage - there is still much brown mixed with the grey.
In addition to their distinctive activities and physical characteristics, they also have some very obvious plumage field marks. Adult males are the Grey Ghosts of the title. It takes them roughly two years to reach their full adult plumage - grey on back, whitish below, tail barred and wingtips "dipped in ink" (see right). They go through a transitional stage with many brownish tones mixed in with the grey, like the bird shown above. Females are brown on back, streaked with brown below. Juveniles of both sexes have brown backs and a rich cinnamon color below. All ages and sexes show the facial disc and (key field mark!) a large white rump patch.
A friend of mine told me about the first harrier she banded. She went to the net, saw the long long legs and the Cleopatra eyes and shouted "I caught a chorus girl!" They have long been a favorite of mine, to the point that they're immortalized on my license plate.
A chorus girl indeed. BTW, you can generally tell juvenile males from females by eye color: males are yellow or grey-yellow, females are usually dark brown.
Bonus: Walter Kitundu's photo of one of the Marin Headlands harriers, this one a true "Grey Ghost".