The Northern Harrier (Circus hudsonius) is a medium-sized bird of prey that breeds throughout Canada, the United States and northern Mexico. It is sometimes known as the “marsh hawk” due to its preference for open habitats like marshes, meadows and grasslands.
Northern Harriers have a varied diet that consists mainly of small mammals, birds, reptiles, amphibians, and insects. As predators, they play an important role in the ecosystem by helping to regulate prey populations. Understanding what animals commonly eat Northern Harriers can provide insights into the natural food web and dynamics of different habitats where these raptors live and hunt.
Some key questions related to the Northern Harrier’s diet include:
What are the main prey items of Northern Harriers?
Northern Harriers are opportunistic hunters and will prey on just about any small animal they can capture. Mammals make up a large portion of their diet. Voles, mice, rats, moles, rabbits, shrews and other rodents are frequently taken. Northern Harriers also regularly hunt small birds such as sparrows, larks and blackbirds nesting on the ground. Snakes, lizards, frogs and large insects like grasshoppers round out their diet.
How do Northern Harriers hunt and capture prey?
Northern Harriers have several adaptations that make them effective hunters across open habitats. Their owl-like facial disc helps them locate prey by sound. They also have excellent vision. Northern Harriers fly low over fields, grasslands and marshes watching and listening for prey activity below. Once detected, they drop swiftly down onto target animals. Their long legs and talons are used to capture and kill prey.
Do Northern Harriers eat other raptors or scavenge food?
While opportunistic scavenging has been recorded, Northern Harriers get most of their food through live prey capture. They do not often consume other bird species. However, they have been known to hunt small owls, American Kestrels and other small raptors on rare occasions. Mammalian carnivores like foxes, raccoons, weasels and coyotes may opportunistically prey on young harriers still in the nest before they can fly.
What impact does habitat and location have on their diet?
Northern Harrier diet can vary across different habitats and regions. In their grassland breeding grounds across Canada and the northern U.S., small rodents tend to dominate. At more southern wintering grounds small mammals remain important prey, but a greater proportion of birds, reptiles and insects may be taken in marshes and open fields. Coastal populations take more birds associated with shore and marsh habitats. throughout their range, Northern Harriers are dietary generalists and consume whatever small prey is abundant in their local habitat.
Major Prey of Northern Harriers
Northern Harriers prey on a wide variety of small animals. Their main food sources can be divided into several categories:
Mammals
Rodents make up the majority of the mammalian prey taken by Northern Harriers. Voles, mice, rats, chipmunks, squirrels, shrews, moles and rabbits are all commonly consumed. Harriers hunt these animals in open habitats like grasslands, marshes, pastures and prairies.
Birds
Northern Harriers prey on various bird species, especially ground nesting songbirds like larks, sparrows and blackbirds. Shorebirds, grouse, quail and young Ring-necked Pheasants may also be taken.
Reptiles and Amphibians
Snakes, lizards, frogs and toads are all opportunistically hunted by harriers, typically in wetland settings.
Insects
Large insects like grasshoppers, dragonflies and beetles are consumed. Caterpillars and grubs may also be preyed upon.
Other Invertebrates
Northern Harriers have been recorded catching earthworms, snails, spiders and other invertebrates to supplement their diet. Carrion is eaten only occasionally.
Hunting Adaptations
Northern Harriers have evolved several key adaptations to help them effectively hunt prey across open country:
Vision and Hearing
Their owl-like facial disc directs sounds towards their ears, allowing them to precisely locate prey. Excellent vision allows them to spot prey from high up.
Low Flight
Slow flight low over the ground helps them spot prey activity below. Their elongated wings allow them to glide and hover.
Stealth
Mottled brown plumage camouflages them from above against dirt and vegetation as they fly low over hunting grounds.
Agility
Long legs and talons are used to swiftly drop down to snatch detected prey. Strong feet help them quickly subdue and kill prey.
Opportunism
As generalist hunters, they will prey on any abundant small animals in the habitats they occupy.
Prey Preferences and Habitat
The specific prey taken by Northern Harriers largely depends on what small animals are most abundant in their particular habitat:
Grasslands
Rodents like voles and mice are preferentially hunted in prairies and fields. Some birds and rabbits are also taken.
Marshes and Wetlands
Birds, frogs, snakes and insects become more common prey items in marshy areas.
Agricultural Areas
Abundant rodents and other small mammals are key prey in agricultural settings like croplands.
Coastal Regions
Shorebirds, wading birds, small mammals and invertebrates are more regularly consumed.
Wintering Grounds
In their more southern wintering areas, reptiles, amphibians and insects may become seasonally important prey.
Across all habitats, Northern Harriers remain flexible and opportunistic, hunting whatever small prey is available. This generalist strategy allows them to thrive across an array of open environments.
Hunting Techniques
Northern Harriers have evolved a number of techniques to effectively hunt across the open habitats they occupy:
Still-hunting
Perching on poles or low branches, Northern Harriers scan below for prey activity. They drop down quickly on detected prey.
Low-flying
Slow flight low over fields and marshlands allows them to spot prey movement. Their facial discs help them pinpoint prey by sound.
Hovering
Rapid wing beats allow Northern Harriers to briefly hover in place to zero in on prey.
Prolonged pursuit
Prey may be chased over land or through marshlands until exhausted before being captured. Strong flying skills allow long chases.
Pounce hunting
From low flight or an elevated perch, Northern Harriers swiftly pounce down onto prey detected below through sight or sound.
Ground pursuit
Prey like rabbits may be pursued on foot through vegetation once knocked to the ground from the air.
Wading
Northern Harriers wade into shallow water to grab aquatic prey like frogs, fish and invertebrates.
This array of hunting techniques allows Northern Harriers to be versatile and opportunistic predators in the areas they inhabit.
Behavior and Feeding Ecology
Understanding the feeding ecology and hunting behaviors of Northern Harriers provides insights into their natural history:
Dietary Composition
Northern Harriers are carnivorous raptors that feed on small vertebrates like rodents, birds, reptiles and amphibians as well as invertebrates. Mammals comprise over 50% of prey items based on observational studies.
Prey Size
Northern Harriers take a wide range prey from mice and voles weighing under 50 grams to ducks, pheasants and rabbits up to 800 grams. Most prey ranges between 100-300 grams.
Hunting Activity
Peak hunting activity occurs in early morning and late afternoon. More time is spent hunting on overcast or rainy days.
Energy Requirements
Northern Harriers require approximately 125-300 grams of prey daily to meet their high energy needs. This is around 25% of their body weight.
Prey Handling
Prey is usually swallowed whole on the ground. Larger items may be torn into pieces before eating. Bones, fur, feathers and exoskeletons are regurgitated as pellets.
Caching
Northern Harriers occasionally cache extra food in shallow holes or vegetation. Cached prey may be eaten later or used to feed nestlings.
Understanding these aspects of their feeding ecology provides deeper insight into their critical ecological role as predators.
Other Predators
As a predator itself, the Northern Harrier may also fall prey to some larger carnivores that share their habitat:
Foxes
Red foxes and gray foxes will predate both young harriers and eggs in ground nests.
Coyotes
Coyotes opportunistically consume young harriers as well as adult harriers they can capture.
Raccoons
Raccoons raid nests and eat eggs and nestlings. They will also prey on roosting adult harriers.
Skunks
Like raccoons, striped skunks consume eggs and vulnerable young of Northern Harriers.
Feral cats
Feral and barn cats stalk and kill young flightless harriers still in the nest.
Other raptors
Larger raptors like eagles, hawks and owls may kill both young and adult harriers.
Mammalian mesopredators seem to be the main threat to Northern Harriers, especially in grassland and wetland areas where they co-occur.
Northern Harriers as Prey
While an effective predator in its own right, the Northern Harrier also serves an important ecological role as prey for other carnivorous animals that share its habitats:
Source of Food
Northern Harriers provide a source of food and energy for larger predators like foxes, coyotes, bobcats and raptors.
Population Control
Predation on Northern Harriers, especially on younger age classes, helps regulate and maintain balance in their populations.
Nutrient Cycling
As prey, Northern Harriers contribute nutrients back into the food web when predators digest and excrete them, or leave remains that decay.
Prey Abundance
The number of Northern Harriers can influence prey numbers. Declines may release prey populations like rodents.
Habitat Selectors
Some predators track and hunt Northern Harriers as “habitat locators” that signal ideal hunting patches.
Serving as prey helps Northern Harriers fulfill their vital ecological role and contribute to ecosystem functioning.
Scavenging
While not a primary feeding strategy, Northern Harriers will scavenge opportunistically:
Carrion
Northern Harriers feed on carcasses of animals like rabbits, squirrels and livestock. This provides an easy meal.
Roadkill
Harriers quickly locate and consume small animals hit by vehicles while driving along roads.
Predator Kills
Northern Harriers steal prey remains left behind by foxes, coyotes, raptors and other predators.
Winter Months
Carrion and roadkill becomes more important in winter when live prey is scarce.
Nest Provisioning
Rotting meat supplements the diet of nestlings. Adults may cache carrion near nests.
Filling Dietary Gaps
Scavenging helps Northern Harriers fill seasonal or localized gaps in live prey availability.
Opportunistic scavenging allows Northern Harriers to supplement their dietary needs, especially when certain prey may be limited.
Impacts on Prey Populations
As predators, Northern Harriers exert various impacts on the populations of animals they prey upon:
Population Reduction
Predation accounts for a significant portion of natural mortality in prey species like voles and sparrows, reducing their numbers.
Population Regulation
By culling sick, old and juvenile prey, Northern Harriers help regulate prey populations, preventing explosive growth.
Prey Density Effects
Heavy predation pressures can suppress prey densities. Declining harrier numbers may increase prey populations.
Evolutionary Pressures
Predation has selected for prey adaptations like camouflage, speed and vigilance to help avoid harrier attacks.
Habitat Influences
Northern Harriers often hunt prey concentrated in optimal habitats. This can alter local prey distribution.
Prey Community Shifts
Differential predation on certain prey species may drive shifts in small mammal and bird community composition.
As key predators, Northern Harriers shape and influence various aspects of prey population ecology across their range.
Ecosystem Role
As predators, Northern Harriers play an important functional role in ecosystem processes:
Trophic Regulation
Northern Harriers help regulate prey populations at lower trophic levels, preventing overgrazing and trophic cascades.
Nutrient Cycling
They recycle nutrients through the food chain as prey is consumed, digested and excreted.
Disease Regulation
Culling sick prey limits disease spread. Scavenging on carrion also limits disease risks.
Bioindicators
Northern Harrier numbers reflect prey abundances and overall ecosystem health. Declines may signal issues.
Mesopredator Release Effect
The loss of harriers may allow prey like rodents and small predators to increase, affecting community structure.
As important mesopredators, Northern Harriers help maintain ecosystem stability and function within the habitats they occupy.
Threats and Conservation
Several factors threaten Northern Harrier populations, highlighting the need for continued conservation:
Habitat Loss
Wetland drainage and grassland conversion have caused breeding population declines.
Agricultural Intensification
Improved pest control, mechanization, earlier haying and increased grazing reduce habitat suitability.
Climate Change
Shifting prey distributions may create habitat mismatches. More frequent droughts and storms also threaten populations.
Human Disturbance
Increasing urbanization, roads, trails and recreational activities near nesting and foraging grounds have reduced nest success.
Pollution
Pesticides reduce prey and may cause direct poisoning. Bioaccumulation of chemicals like mercury may also threaten health.
Maintaining suitable habitat and mitigating human disturbance will be key conservation priorities going forward. Careful monitoring of populations should continue.
Conclusion
In summary, Northern Harriers are opportunistic predators that help regulate prey populations, contribute to ecosystem functioning, and serve as prey for other species across the open habitats they occupy. Their varied diet is influenced by regional habitat and consists mainly of small mammals, birds, reptiles and amphibians. Hunting adaptations like keen sight and hearing allow them to effectively capture prey in flight and bolster their vital ecological role. However, habitat loss, human disturbance and other factors have caused population declines that require ongoing conservation efforts. Understanding details of the Northern Harrier’s feeding ecology provides critical insights into their natural history and importance within natural communities.
