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Northern Harriers: The Ghosts of Mercer Meadows

Northern Harriers are among North America’s most unusual birds of prey. Unlike Red-tailed Hawks, which often perch high in trees or on telephone poles while watching for prey, harriers spend much of their hunting time flying low over fields and marshes. Their slow, buoyant flight is unmistakable once you’ve learned to recognize it.

And if you’re fortunate enough to spot an adult male, you may understand why birdwatchers have given him one of the most evocative nicknames in the bird world, the ‘Gray Ghost’.

Male and female Northern Harriers look so different that it’s easy to mistake them for separate species.

Adult males are striking birds, with pale silver-gray feathers across their backs and wings, white undersides, and dramatic black wingtips. In the soft light of a winter afternoon, their nearly silent flight over the meadows can give them an almost ghostly appearance.

Females, on the other hand, are considerably larger and predominantly brown, with streaked buff-colored undersides. Juvenile harriers resemble females but often have rich cinnamon-colored underparts.

This difference in size is particularly interesting. Female Northern Harriers can weigh nearly twice as much as males, an example of reverse sexual size dimorphism, a characteristic found in many birds of prey.

Both sexes share one distinctive field mark: a conspicuous white rump patch that is especially visible when the bird banks or turns in flight.

A Hawk With the Face of an Owl

One of the Northern Harrier’s most remarkable adaptations is something you might not notice without a close look at its face.

Like owls, harriers possess a facial disc—a ring of specialized feathers surrounding the face that helps collect and direct sound toward the ears.

Most hawks depend primarily on their extraordinary eyesight to locate prey. Northern Harriers also rely heavily on hearing, allowing them to detect small mammals moving through dense grasses, even when the animals are partially hidden from view.

Their facial discs are less pronounced than those of most owls, but they serve a similar purpose. The result is a bird that combines the keen eyesight of a hawk with some of the sound-detecting abilities we usually associate with nocturnal hunters.

The harrier’s owl-like face also gives it a distinctive expression, quite different from the fierce, angular appearance of many other hawks.

Masters of Low-Level Flight

Northern Harriers have a hunting style all their own. Rather than soaring high overhead, they typically cruise just a few feet above the ground, moving back and forth across open fields.

Their long wings and relatively light bodies allow them to fly slowly without stalling, while their long tails help them make quick adjustments in direction.

When a harrier detects a mouse, vole, or other small animal, it may suddenly drop into the vegetation, extending its long legs and sharp talons to seize its prey.

Small mammals make up much of their diet, particularly meadow voles, but harriers also take small birds, reptiles, and occasionally large insects.

Their hunting flights often follow a loose, wandering pattern (like they’re leaving the bar after last call), with the bird repeatedly changing direction as it searches the grasses below. To an observer, it can appear almost effortless, although the harrier is actually making precise adjustments to its speed and position.

A Rivalry in the Meadows

Northern Harriers aren’t the only birds of prey hunting the grasslands of Mercer Meadows. During the winter months, they share this habitat with Short-eared Owls (which have also been featured in an article on this site), another remarkable species that specializes in hunting small mammals, particularly meadow voles.

The two species have surprisingly similar hunting styles. Both fly low over open fields, using keen hearing to detect prey hidden beneath the grasses. And while harriers generally hunt during daylight and Short-eared Owls are most active around dusk and dawn, their schedules frequently overlap in the late afternoon.

That’s when things can get interesting!

Northern Harriers and Short-eared Owls are known to engage in dramatic aerial confrontations, sometimes chasing, diving at, and harassing one another over the fields. These encounters may involve competition for hunting territory or attempts to steal captured prey, a behavior known as kleptoparasitism.

Occasionally, a bird carrying a freshly caught vole will find itself pursued by a hungry competitor, resulting in an aerial skirmish as the two maneuver above the meadow.

For birdwatchers, these encounters can be spectacular. Watching a Northern Harrier and a Short-eared Owl twist and turn through the evening sky is a reminder that even the quietest winter meadow can be the setting for some surprisingly intense wildlife drama.

The open grasslands around the Pole Farm provide a perfect habitat for both species, although Short-eared Owls are more uncommon and their presence varies from year to year. Late afternoon and dusk offer the best chance of observing their overlapping hunting activity.

From Bird to Fighter Jet

The name “Harrier” has an interesting connection to aviation.

The famous British Harrier jump jet, developed during the 1960s, takes its name from this group of low-flying birds of prey.

The aircraft became famous for its ability to take off and land vertically, as well as operate from short runways and aircraft carriers. Its maneuverability and low-level attack role made the name particularly appropriate.

The connection is primarily one of naming and inspiration rather than a direct imitation of the bird’s anatomy or flight mechanics. Northern Harriers cannot hover in place like a helicopter, and the jet’s vertical takeoff technology wasn’t copied from the bird.

Still, anyone who has watched a harrier skim effortlessly across a meadow can appreciate why aviation designers found the name appealing.

Where to See Northern Harriers Along the Lawrence Hopewell Trail

The open grasslands of Mercer Meadows, particularly the historic granja de postes, provide some of the best opportunities along the Lawrence Hopewell Trail to observe Northern Harriers.

Unlike the woodpeckers that favor the trail’s wooded sections, harriers prefer broad, open landscapes with relatively little tree cover.

The extensive fields around the Pole Farm offer exactly the kind of habitat these birds use for hunting.

Northern Harriers are most likely to be encountered in Mercer County during fall, winter, and early spring. Although the species breeds in parts of New Jersey, it is primarily a winter visitor to the Mercer Meadows area.

Late afternoon can be an especially rewarding time to look for them, when harriers may be actively hunting before settling into their nighttime roosts.

When scanning the fields, watch for a large, slender-winged bird flying low over the grasses with its wings raised slightly above horizontal. A flash of white at the base of the tail is often the easiest way to confirm its identity.

And keep an eye out for the Gray Ghost. Adult males are particularly memorable against the muted browns and golds of the winter meadows.

Protecting Our Grassland Hunters

Northern Harriers depend on open grasslands, marshes, and other expansive habitats that have become increasingly scarce throughout the northeastern United States.

As fields are developed or gradually replaced by forests, suitable hunting and nesting areas disappear. Ground-nesting birds such as harriers are also vulnerable to disturbance, particularly during the breeding season.

The preserved grasslands of Mercer Meadows provide valuable habitat not only for Northern Harriers but also for American Kestrels, Eastern Meadowlarks, and many other species associated with open country.

For visitors to the Lawrence Hopewell Trail, these landscapes offer an opportunity to experience a different side of New Jersey’s birdlife—one dominated not by woodland songbirds, but by the remarkable hunters of the open sky.

And on a quiet winter afternoon, when a pale gray shape drifts silently across the fields, you’ll know you’ve encountered one of Mercer County’s most elegant winter visitors.