The Northern Harrier (Circus hudsonius) is a medium-sized raptor found throughout much of North America. As with most bird species, Northern Harriers have a variety of natural predators that help keep their populations in balance. In this article, we will explore the main predators of the Northern Harrier and how they hunt and kill these birds. Understanding the threats faced by the Northern Harrier can help us better protect and conserve this unique raptor species.
Main Predators of the Northern Harrier
The Northern Harrier faces predation during all stages of its life cycle. The main natural predators of Northern Harriers include:
Great Horned Owls
The Great Horned Owl (Bubo virginianus) is one of the most common and formidable predators of the Northern Harrier. These large and powerful owls prey on both adult and young harriers. Great horned owls hunt at night using their excellent low-light vision and hearing. They capture roosting harriers by surprise attack.
Red-Tailed Hawks
Red-tailed Hawks (Buteo jamaicensis) occasionally prey on Northern Harriers, especially young fledglings and injured adults. Red-tails are adept at hunting on the wing, and may chase down harriers in flight. Their powerful talons can inflict lethal damage.
Peregrine Falcons
The fast-flying Peregrine Falcon (Falco peregrinus) poses a threat to Northern Harriers during the breeding season when the harriers are busy hunting to provision their chicks. Peregrines can chase down and kill harriers in mid-air with their speed and deadly talons.
Coyotes
Coyotes (Canis latrans) are opportunistic predators that sometimes eat Northern Harrier eggs and chicks. Coyotes raid harrier nests on the ground and have been documented destroying entire clutches. They may also prey on injured fledglings.
Raccoons
Like coyotes, raccoons (Procyon lotor) are major nest predators of Northern Harriers. Using their dexterous paws, raccoons access harrier nests and eat the eggs. Raccoons can decimate Northern Harrier breeding productivity in areas where they are common.
Snakes
Certain snake species like rat snakes and gopher snakes are known to eat Northern Harrier eggs and nestlings. Snakes can slip into harrier nests on the ground and swallow the eggs whole. Young chicks are also vulnerable to snake predation.
Feral Cats
In some regions, feral and free-roaming domestic cats can take a heavy toll on nesting Northern Harriers. Cats are adept at finding well-hidden nests on the ground and will eat both eggs and chicks. Cats may also prey on fledglings.
Other Predators
Additional predators of Northern Harriers can include squirrels, skunks, crows, ravens, gulls, and bears. Predation pressure varies regionally based on the local predator abundances. The common factor is that most predators target the eggs and chicks in the nest before the young can fledge and fly.
How Different Predators Hunt and Kill Northern Harriers
The hunting strategies and kill methods used by Northern Harrier predators are adapted for how they capture bird prey. Here is an overview of how some key harrier predators attack and kill:
Great Horned Owls
Great horned owls primarily hunt resting or roosting harriers at night. Their tactic is to use stealth and surprise. Great horned owls will fly silently on their large, muffled wings to approach undetected. At close range, they plunge down talons-first to pierce and kill the harrier. The crushing power of their talons causes massive trauma. Great horned owls then carry the harrier off to eat or feed their young.
Red-Tailed Hawks
Red-tails most often catch Northern Harriers while in flight during the daytime. Both species are adept fliers, so the red-tails must rely on their speed and aerial agility to chase down the harrier from behind or the side. Once in close pursuit, the red-tailed hawk uses its large talons to grab and puncture the harrier. If not instantly killed, injured harriers are then finished off on the ground.
Peregrine Falcons
Peregrine falcons are all about speed in their hunting strategy. When targeting Northern Harriers in flight, peregrines will stoop down in a steep dive that can exceed 200 mph. At this speed, their impact is extremely forceful and usually fatal. Peregrines strike the back or wing musculature of the harrier to cripple its flight before binding the prey with their talons. If the initial strike does not kill the harrier, the peregrine quickly dispatches it with bites to the neck with their sharp, hooked beak.
Coyotes and Raccoons
As terrestrial predators, coyotes and raccoons rely on their senses of smell and hearing to locate Northern Harrier nests hidden in vegetation on the ground. Once they pinpoint the nest location, coyotes and raccoons use their front paws to scatter the materials and expose the eggs or chicks. The eggs are crushed in the jaws or the chicks shaken violently to kill them. Coyotes and raccoons are opportunistic foragers and can destroy entire harrier clutches and broods if given the chance.
Snakes
Snakes locate Northern Harrier nests through chemical cues from the birds and eggs. Like coyotes and raccoons, snakes eat the eggs and chicks directly in the nest. Their flexible jaws allow snakes to swallow the eggs whole. For chicks, snakes use constriction to kill them before eating them. Snake predation can be difficult to detect since they leave minimal disturbance to the nest structure itself.
Defense Mechanisms Northern Harriers Use Against Predators
Northern Harriers have some adaptations and behaviors that help protect them against predators and reduce losses:
Camouflaged Plumage
The plumage of the Northern Harrier provides excellent camouflage as they nest and hunt in open grasslands, marshes, and fields. The mix of brown, buff, and white coloration blends in with the ground and vegetation. For ground nests, this helps conceal the eggs and chicks from visual predators like coyotes, foxes, and feral cats. Their camouflage also helps harriers conceal themselves from potential predators while hunting.
Mobbing
Adult Northern Harriers may perform mobbing behavior against potential nest predators like crows, ravens, raccoons, and snakes. The harriers will dive aggressively at the threat while vocalizing loudly. This helps drive the predator away by demonstrating that the harriers are alert and willing to attack. Mobbing alerts the predator that it has been detected and tries to scare it off before it locates the nest.
Distraction Displays
One unique anti-predator adaptation by parent Northern Harriers is distraction displays. If a predator approaches or discovers the nest, the parent harrier may perform exaggerated injury-feigning behaviors like dragging wings or flopping around on the ground. This distracts predators and lures them away from the nest location to give the eggs or chicks greater chance of survival.
Remote Nest Sites
Northern Harriers typically choose nest sites far from human activity and areas frequented by predators like coyotes and foxes. Nesting in remote locations away from forest edges and built-up areas can help deter some predators. However, wide-ranging predators like great horned owls still pose a threat.
Aggressive Defense
Female Northern Harriers in particular are aggressive in defending the nest against potential predators. They will attack animals like foxes, coyotes, and feral cats that get too close. While a harrier is unlikely to kill such predators, their aggression may startle or deter some animals from attempting to raid the nest. The male typically assists in nest defense as well.
Early Fledging
Northern Harrier chicks leave the nest at 25-30 days old, sometimes earlier if the nest is disturbed. Fledging at an early age shortens the period that the chicks are vulnerable in the nest and unable to fly away from terrestrial predators. Once mobile, the chicks are harder to locate and catch.
Northern Harrier Population Impacts from Predation
Predation on Northern Harriers can significantly influence overall population numbers, reproduction, and geographic distribution:
Lower Reproductive Rates
Heavy losses of eggs and chicks to nest predators like raccoons, coyotes, and snakes reduce the number of young produced each breeding season. With fewer juveniles surviving to adulthood each year, predation directly lowers harrier reproductive rates.
Adult Mortality Rates
Predators that kill adult harriers like great horned owls and red-tailed hawks increase overall mortality rates. This cuts short the breeding tenure of those adults. Excessive predation pressures can tip the balance toward population declines.
Shift Nesting Locations
High levels of nest predation may cause Northern Harriers to change nesting locations over time. Harriers may shift away from areas with an abundance of predators toward safer sites. However, habitat loss limits available nesting areas.
Declining Population Trends
In areas of Canada and parts of the western United States, predation is linked to declining harrier populations. Lack of suitable habitat also exacerbates harrier losses to predators. Careful management of landscape conditions is needed.
Localized Extirpation
At a more localized level, predation may lead to Northern Harriers disappearing from specific areas. Nests and adults concentrates in a small region can be hit hard by certain predator populations. The harriers may fail to persist as breeders without immigration from larger source populations.
Conclusion
Northern Harriers face substantial natural predation pressure from a diversity of raptors, mammals, snakes, and other wildlife species. Predators are an inherent part of the ecosystem, but excessive mortality can negatively impact harrier numbers. Habitat loss also concentrates harriers and makes them more vulnerable. Maintaining suitable breeding conditions, limiting destructive predators like feral cats where possible, and preserving connectivity between source populations can help counter high predation rates. With thoughtful management, the unique Northern Harrier can remain a part of grassland and wetland communities into the future.
