The Northern Harrier (Circus hudsonius) is a medium-sized raptor found across North America and parts of South America. This slender, long-winged hawk is best known for its aerial acrobatics and buoyant flight low over open fields and marshes as it searches for small mammals, birds, reptiles, and insects.
Once a common sight coast to coast, the Northern Harrier has experienced significant population declines in recent decades. Habitat loss, degradation, and fragmentation have reduced nesting and foraging areas. Widespread use of agricultural pesticides has also taken a toll, reducing prey populations and impacting harrier reproduction. Due to these threats, the Northern Harrier is considered a species of conservation concern across its range. Understanding why this unique raptor is declining can help inform ongoing conservation efforts for the species.
Natural History
The Northern Harrier ranges across most of North America, from Alaska and Canada south to northern Mexico and the Florida Keys. It frequents open habitats like grasslands, wetlands, pastures, marshes, and agricultural fields.
Northern Harriers nest on the ground, building a platform nest out of sticks, grasses, and other vegetation. Nest sites are typically located in dense, tall vegetation that provides cover. The female lays 3-9 eggs that incubate for about 32 days. The male supplies most of the food during incubation and the first few weeks after hatching. The young fledge the nest at around 35 days old but remain dependent on the parents for several more weeks as they learn to hunt on their own.
These hawks get their common name from their habit of harrying, or flushing out, prey as they fly low over fields. Their owl-like facial discs focus sound to aid in locating small mammals and birds in vegetation below. Long legs and tails provide stability and maneuverability during their acrobatic hunting flights.
Northern Harriers prey on a variety of small animals including voles, mice, shrews, snakes, lizards, frogs, small birds, and large insects. They will also eat carrion when available. Their dietary flexibility allows them to thrive across diverse habitats and changing prey availability.
Population Threats
The Northern Harrier has experienced steep declines over the past several decades. The primary threats facing this species include:
Habitat Loss and Degradation
Wetland drainage, development, and conversion of grasslands for agriculture have destroyed and degraded nesting and foraging habitat across the harrier’s range. They require large open spaces with adequate cover for nesting and abundant prey. Loss of suitable habitat has reduced available nest sites and food resources.
Fragmentation
Remaining habitat has become fragmented into smaller, disconnected patches. Harriers are less likely to settle and breed in small habitat fragments. Fragmentation also impedes foraging over the large areas required to find adequate prey.
Agricultural Intensification
Increased use of pesticides, mechanization, and reversion of grasslands to forest or development have reduced prey availability and nesting sites in agricultural regions.
Climate Change
Climate change and associated habitat shifts may affect prey populations and vegetation structure, further altering nesting and foraging conditions. Rising sea levels also threaten important coastal habitats.
Disturbance
Northern Harriers avoid nesting near human disturbance and activity. Noise, roads, trails, turbines, and other disruptions render some areas unsuitable for nesting and foraging.
Pollution
Environmental contaminants like pesticides, PCBs, and heavy metals have been detected at elevated levels in Northern Harrier eggs and tissues. These toxins can lead to eggshell thinning and embryo deformities.
Data Deficiencies
Lack of robust monitoring, population indices, and demographic data make it difficult to fully assess the conservation status of the Northern Harrier across its full range. More research is needed to fill information gaps.
Conservation Status
Due to significant population declines, the Northern Harrier is listed as threatened, endangered, or a species of special concern in many states and provinces. Partners in Flight estimates the global breeding population has declined by >50% since 1970. The 2016 State of North America’s Birds report lists the Northern Harrier as a Common Bird in Steep Decline.
IUCN Red List Classification:
- Least Concern
The IUCN Red List is the global authority on the conservation status of plant and animal species. Despite steep declines, the Northern Harrier is currently classified as Least Concern due to its large range and total population size. However, the IUCN indicates the population trend is decreasing and recognizes habitat loss as a threat.
Federal Protection:
- United States: None
- Canada: Threatened
- Mexico: Threatened
The Northern Harrier has no special federal conservation status in the U.S. However, it is listed as Threatened under Canada’s Species at Risk Act and Mexico’s endangered species law. This provides legal protections and requires recovery planning in those countries.
Organization | Conservation Status |
---|---|
IUCN Red List | Least Concern |
United States | None |
Canada | Threatened |
Mexico | Threatened |
Conservation Actions Needed
To stabilize and restore Northern Harrier populations, conservation actions should include:
Habitat Protection and Management
– Prioritize protection and management of remaining grasslands, wetlands, and open habitats on public and private lands.
– Maintain suitable vegetation structure and prey populations.
– Establish protected habitat corridors connecting fragmented areas.
Sustainable Agriculture Practices
– Provide outreach programs to support raptor-friendly methods on farms and ranches.
– Limit pesticide use in known nesting areas.
– Maintain cultivated grasslands and field edges with adequate prey and cover.
Establish Protected Areas
– Secure habitat reserves and easements in core breeding areas through acquisition, donation, or cooperative agreements.
Reduce Human Disturbance
– Restrict human activities near nest sites during the breeding season.
– Site trails, roads, wind turbines, and other infrastructure away from key habitat.
Population Monitoring
– Implement standardized surveys, banding, and demographic studies to detect population trends.
– Identify high priority areas for research and monitoring.
Outreach and Education
– Provide programs, interpretive nature trails, and viewing sites to promote public interest in harriers.
– Engage landowners and communities in voluntary habitat conservation programs.
The Outlook for Northern Harriers
Targeted conservation action can still make a difference for the Northern Harrier. While some declines will be difficult to reverse in the short term, stabilizing populations and protecting habitat can prevent extirpations and future endangered species listings. Maintaining North America’s remaining grasslands, wetlands, and working agricultural lands will be key. With appropriate habitat management, reduced pesticide threats, stronger legal protections, and conservation incentives for landowners, Northern Harrier populations can once again take flight.
Conclusion
The Northern Harrier is declining primarily due to widespread habitat loss, degradation, fragmentation, and reduced prey populations across its breeding range. Agricultural intensification, human disturbance, pollution, climate change impacts, and lack of data on populations also threaten this unique raptor. Listing the species as federally threatened in the U.S. and Canada would spur expanded monitoring and habitat protections. Outreach, sustainable land management incentives, and reserves in core areas can also help stabilize populations. With a focused conservation effort, the Northern Harrier’s amazing aerial hunting displays can continue captivating bird enthusiasts and sustaining healthy grassland ecosystems.