The Northern Harrier (Circus hudsonius) is a medium-sized raptor found across North America. Once a common sight in grasslands and marshes, Northern Harrier populations declined significantly in the 20th century due to habitat loss and pesticide use. However, with increased conservation efforts in recent decades, Northern Harriers have begun to recover in some parts of their range. Determining current global and regional population sizes and trends is an important part of monitoring the success of these conservation efforts.
What is the global population of Northern Harriers?
The global population of Northern Harriers is estimated to be 1 million to 3 million individuals. The species has an extremely large range across North and South America. However, Northern Harriers are generally uncommon to rare across their range.
More specifically, population estimates include:
- North America: 500,000 to 1 million breeding individuals
- Canada: 100,000 to 500,000 breeding individuals
- United States: 200,000 to 700,000 breeding individuals
- Mexico: 50,000 to 100,000 breeding individuals
- Central and South America: 250,000 to 1 million breeding individuals
These totals suggest a global population likely in the range of 1-3 million Northern Harriers, though the estimates have high uncertainty due to the challenges of surveying this species across its vast range. Overall, Northern Harriers remain common in some regions, but are declining in areas with heavy habitat loss.
What is the population trend of Northern Harriers?
Northern Harrier populations declined significantly in the 20th century. The widespread use of organochlorine pesticides such as DDT caused eggshell thinning andnesting failures, severely reducing Northern Harrier numbers. For example, in the 1940s there were an estimated 25,000 breeding pairs in California, but only 300 remained by the 1970s.
With the banning of DDT and other pesticides in the 1970s, as well as increased habitat conservation efforts, Northern Harrier populations have rebounded in many regions. Breeding Bird Survey (BBS) data from 1966-2019 shows:
- Across North America, Northern Harriers increased by +2.1% per year over this period
- In the Western BBS region, the population increased by +3.6% per year
- In the Eastern BBS region, the population increased by +1.5% per year
So while global populations likely remain below historical levels, Northern Harriers are recovering well in many areas thanks to conservation actions. Continued monitoring is needed to ensure this positive trend continues.
Northern Harrier Population Trends by Region
Here is a closer look at population trends across the Northern Harrier’s range:
Canada:
- Increased by +2.5% per year from 1968 to 2012 across Canada
- Population strongholds remain in prairie provinces like Alberta and Saskatchewan
United States:
- Increased by +2.1% per year from 1966 to 2015
- Greatest increases in western states like Idaho, Oregon, Nevada
- Declines in mid-Atlantic states like New York, Pennsylvania
Mexico:
- Unknown overall trend, variable by region
- Declining in central highlands
- Increasing in grasslands of northern Mexico
Central and South America:
- Insufficient data on population trends
- Presumed stable to increasing in most regions
Overall, Northern Harrier populations generally appear to be stable or increasing through most of North America, although continued monitoring is important in regions that are still declining. Expanding grassland habitat and limiting pesticide use remain key conservation priorities for the species across its range.
Why are Northern Harrier populations increasing in some areas?
Several key factors have driven the recovery of Northern Harrier populations in many regions since the 1970s:
Banning of DDT and Other Pesticides
The EPA ban on DDT use in 1972 was critical for reversing the sharp declines in Northern Harriers and other raptors. With reduced pesticide contamination, eggshell thinning and nest failures decreased, allowing populations to recover. Ongoing restrictions on pesticide use in the U.S. and Canada continue to benefit Northern Harriers today.
Expansion of Conservation Reserve Program (CRP)
The CRP pays farmers to restore grasslands and wetlands on agricultural lands, creating ideal Northern Harrier habitat. CRP enrollment peaked at over 36 million acres in 2007, greatly increasing breeding habitat for Northern Harriers. However, recent declines in CRP enrollment threaten these habitat gains.
Wetland Protections and Restoration
Federal wetland protections help conserve Northern Harrier habitats. Projects restoring wetlands and grasslands have also expanded habitat, including over 9 million acres of wetlands restored in the U.S. through the North American Wetlands Conservation Act.
Increased Public Interest in Raptor Conservation
Northern Harriers and other raptors have benefited from increased public appreciation of birds of prey. Numerous raptor conservation and education programs involving Northern Harriers have boosted awareness and protection efforts.
Range Expansion
Northern Harriers have expanded their breeding range northward in Canada, colonizing new regions as climate change facilitates range shifts. However, some southern populations in the U.S. remain in decline.
What conservation actions are needed to protect Northern Harriers?
While Northern Harrier populations have rebounded from historical lows, active conservation is still needed to aid their recovery. Some key conservation priorities include:
Habitat Protection and Management
- Protect grasslands and wetlands through acquisition, easements, or incentive programs
- Implement grazing, burning, and mowing regimens to maintain suitable vegetation structure
- Restore native plant communities where needed
Sustainable Agriculture Practices
- Encourage bird-friendly grazing regimes, cover crops, and reduced mowing
- Expand programs like CRP to restore grassland habitat on farmlands
- Limit pesticide use through integrated pest management
Monitoring and Research
- Continue long-term surveys like the Breeding Bird Survey
- Study impacts of habitat loss, pesticides, climate change, and more
- Track migration patterns and wintering grounds
Education and Outreach
- Engage landowners, farmers, and the public in raptor conservation
- Share information on Northern Harriers to build awareness and support
- Train students and community scientists in raptor monitoring
Through continued habitat conservation, environmental policies, research, and public education, Northern Harrier populations can hopefully be restored to more robust levels across North America.
Northern Harrier Population Data Summary
Here is a summary of the key Northern Harrier population figures and trends:
Region | Population Estimate | Population Trend |
---|---|---|
Global | 1 million to 3 million | Likely increasing overall since 1970s |
North America | 500,000 to 1 million | Increasing +2.1% per year |
Canada | 100,000 to 500,000 | Increasing +2.5% per year |
United States | 200,000 to 700,000 | Increasing +2.1% per year |
Mexico | 50,000 to 100,000 | Variable by region |
After major declines in the 20th century, Northern Harrier populations appear to be recovering in many regions thanks to conservation actions. Continued habitat protection, environmental policies, research, and education efforts are still needed to aid this recovery and stabilize populations. With appropriate management, Northern Harriers can thrive again across the grasslands and marshes of North America.
Conclusion
In summary, current global population estimates suggest there are likely 1-3 million Northern Harriers remaining worldwide. After severe declines in the 1900s from pesticides and habitat loss, Northern Harrier populations are now recovering in many parts of their range, increasing at around 2% per year in North America based on long-term monitoring data. However, continued conservation action is still needed to protect habitat and support sustainable populations. The Northern Harrier’s unique adaptation to open grasslands and marshes means protecting this species also benefits many other grassland wildlife and ecological communities. With appropriate habitat management, environmental policies, and public engagement, Northern Harrier populations can hopefully be restored to robust levels, allowing these graceful harriers to once again thrive across North American skies.