IUCN 10/01/2016 – Least Concern (LC), Population Trend Decreasing

U.S. and Canada Conservation Status: Critically imperiled in 13/66 states and provinces (AR, AZ, CT, DE, IL, KY, NC, NH, NJ, NN, RI, VA, WV). Imperiled in 15/66 states and provinces (AZ, DC, IA, IN, KS, KY, MA, MD, MO, NM, OH, PA, TX, VA, WI). Vulnerable in 21/66 states and provinces. Apparently secure in 33/66 states and provinces. Secure in 6/66 states and provinces.

The data used in this figure are listed above. These data were compiled from NatureServe and the U.S. Fish and Wildlife Service.

Listed as a Species of Special Concern in Vermont, Michigan, and Wisconsin. Species of Management Concern in large portions of the species’ range in the United States.

From Alaska and Canada down to Panama and Colombia.

Open wetlands, marshes, lightly grazed pastures, old fields, tundras, praries, and croplands.

Along with many other raptor species, Northern Harrier populations were likely negatively impacted by human persecution and the use of DDT, with eggshell thickness being significantly lower from 1947 to 1969. Following the DDT ban in the 1970s and protection under the Migratory Bird Treaty Act of 1972, Northern Harrier migration trends were already rebounding. In the East, Northern Harrier counts at Hawk Mountain Sanctuary began to show a slight increase from 1935 onward with number reaching a peak in 1980 and 10 years later at 1990 at Cape May, New Jersey. Northern Harrier migration counts started declining again in the mid 1980s at Hawk Mountain Sanctuary and in the mid 1990s at Cape May. Since the 1990s migration counts at both sites have dropped below DDT era numbers. Christmas Bird Count shows similar continuous declines, although the areas of decline have shifted between 10, 20, and 50 year increments. Trends at Hawk Ridge, Minnesota and and other western sites remain stable in the recent decade but were higher in the 1990s.

These maps summarize the latest RPI trend analyses for count sites throughout North America.

Find the interactive version of the Christmas Bird Count (CBC) maps here.

BBS: Northern Harrier breeding bird trends have been scattered across the survey range. Low credibility throughout the survey range except for Saskatchewan, where numbers have been consistently dropping since the study began in the late 60s.

The main speculation for the cause of consistent Northern Harrier declines is loss of habitat due to the continued, widespread loss of healthy wetland and marshland ecosystems. Some other possible contributors are changes in agricultural use practices, loss of prey species, environmental contaminants, and infectious disease. West Nile virus has increased in Canada and the Northeastern United States. Northern Harriers are vulnerable to the virus, which can result in mortality (Nameth et al, 2007 ). Recent increases in wildfire frequency and intensity may also impact Western populations, though there is no consistent evidence across data sets to show declines have occurred in the West.

Although billions of dollars have been allocated to wetland protection and restoration, wetlands continue to decline in quality and abundance across North America. Global coastal wetlands have lost more than 50% of area in the 1900s, and losses were further accelerated in the last three decades due to aquaculture, urbanization, harbor and navigation channel construction, and sea level rise among other factors (Li et al, 2018). It is predicted that three million birds have been lost in coastal wetland biomes, which includes Northern Harrier populations and their prey base. Acres of prairies and grasslands across North America also have been rapidly declining. From 2008 to 2012, 77% of new cropland in the United States came from grasslands. North American grassland biomes have experienced the greatest net loss of bird species abundance since the 1970s of any biome in the continent. Global climate change is further predicted to impact North America’s grassland regions, with more than 70% of grassland birds having some vulnerability to climate change (Wilsey et al, 2018).

“Clean” farming trends with very large fields of row crops planted fence to fence without traditional tree lines, hedge rows, or brushy areas fail to provide suitable habitat and prey resources for Norther Harriers. Nests can be destroyed by livestock trampling, haying, early mowing, and other agricultural practices, Some preliminary research has shown raptors may not use nesting habitat after a wildfire, which suggests raptors have experienced further declines in usable habitat due to increased fires in the West, although there is not consistent evidence that Northern Harriers are declining in the West region (Gao, 2020).

Northern Harriers could be exposed to a variety of contaminants on breeding and wintering areas. Although the use of organochlorines in North America have become heavily regulated, the continuing effects of other agrochemicals including pesticides and herbicides on Northern Harriers have not been satisfactorily explored. Across the continent, eggshell thickness and mass were significantly lower for this species between 1947 to 1969. Reproductive failure and population declines during that time period were linked to the use of DDT and the resulting DDE. Lead poisoning may also be an issue because adult Northern Harriers will scavenge dead or dying birds and mammals. Consumption of lead shot from waterfowl and game birds can cause Norther Harriers to suffer lead toxicity and poisoning. Anti-coagulant rodenticides (ARs) also can travel up the food chain and have fatal impacts on Northern Harriers and their chicks. Northern Harriers primarily feed on small mammals during winter in the northern part of their range, specifically Microtus voles and they could be particularly vulnerable to ARs. The continued use of ARs in North America related to urbanization and cattle density has resulted in significant raptor mortalities (López -Perea et al, 2019; Murray, 2017). Because some harriers and their songbird prey migrate out of the United States in winter, Northern Harriers also could be exposed to DDT, DDE, and other agrochemicals still being used Central and South America.

During wintering in southeastern coastal marshes, Northern Harriers will primarily feed on passerines and waterbirds. Passerines and small waterbirds also make up a portion of their diet in the summer. The depletion of native grassland bird populations in North America due to habitat loss and more toxic pesticide use in both breeding and wintering areas mirrors loss of farmland birds throughout Europe and elsewhere. In North American grasslands, 480 billion birds have been lost since the 1970s,and the total number of birds has plummeted in the last 50 years, by nearly three billion across North America (Rosenberg et al., 2019). More research is needed to examine if songbird predators, including the Northern Harriers are affected by the drop in prey abundance.

Literature Cited

Bednarz, J. C., D. Klem Jr., L. J. Goodrich, and S. E. Senner. (1990). Migration Counts Of Raptors At Hawk Mountain, Pennsylvania, As Indicators Of Population Trends, 1934-1986. The Auk, 107, 96–107.

Bolgiano, N. (2019). Evidence for West Nile Virus-Related Avian Declines in Pennsylvania. Pennsylvania Birds, 33(1), 2-11.

Farmer, C. J., and Hussell, D. J. (2008). The raptor population index in practice. State of North America’s birds of prey. Series in Ornithology, (3), 165-178.

Farmer, C. J., and Smith, J. P. (2010). Seasonal differences in migration counts of raptors: Utility of spring counts for Population Monitoring. Journal of Raptor Research, 44(2), 101–112. https://doi.org/10.3356/jrr-09-31.1

Fink, D., T. Auer, A. Johnston, M. Strimas-Mackey, O. Robinson, S. Ligocki, W. Hochachka, L. Jaromczyk, C. Wood, I. Davies, M. Iliff, and L. Seitz. (2021). eBird Status and Trends, Data Version: 2020; Released: 2021. Cornell Lab of Ornithology, Ithaca, New York. https://doi.org/10.2173/ebirdst.2020

Gao, J. (2020). (master’s thesis). Effects of Woolsey Fire on Nesting Territories of Southern California Red-Tailed Hawks (Buteo jamaicensis). Oregon State University. Retrieved 2022, from https://ir.library.oregonstate.edu/concern/graduate_projects/5d86p6213.

Lark, T. J., Salmon, J. M., and Gibbs, H. K. (2015). Cropland expansion outpaces agricultural and biofuel policies in the United States. Environmental Research Letters, 10, 044003.

Li, X., Bellerby, R., Craft, C., and Widney, S. E. (2018). Coastal wetland loss, consequences, and challenges for restoration. Anthropocene Coasts, 1–15. https://doi.org/10.1139/anc-2017-0001

López-Perea, J. J., Camarero, P. R., Sánchez-Barbudo, I. S., and Mateo, R. (2019). Urbanization and cattle density are determinants in the exposure to anticoagulant rodenticides of non-target wildlife. Environmental Pollution, 244, 801–808. https://doi.org/10.1016/j.envpol.2018.10.101

Master, L., Faber-Langendoen, D., Bittman, R., Hammerson, G. A., Heidel, B., Ramsay, L., Snow, K., Teucher, A., and Tomaino, A. (2012). NatureServe conservation status assessments: Factors for evaluating species and ecosystem risk. NatureServe, Arlington, Virginia.

Meehan, T.D., LeBaron, G.S., Dale, K., Krump, A., Michel, N.L., and Wilsey, C.B. 2020. Abundance trends of birds wintering in the USA and Canada, from Audubon Christmas Bird Counts, 1966-2019, version 3.0. National Audubon Society, New York, New York, USA.

Murray, M. Anticoagulant rodenticide exposure and toxicosis in four species of birds of prey in Massachusetts, USA, 2012–2016, in relation to use of rodenticides by pest management professionals. Ecotoxicology 26, 1041–1050 (2017). https://doi.org/10.1007/s10646-017-1832-1

Nemeth, N.M., Kratz, G.E., Bates, R., Scherpelz, J.A., Bowen, R.A., and Komar, N. (2009). Clinical evaluation and outcomes of naturally acquired West Nile virus infection in raptors. J. Zoo Wildl. Med. 40, 51–63.

Rosenberg, K. V., Dokter, A. M., Blancher, P. J., Sauer, J. R., Smith, A. C., Smith, P. A., Stanton, J. C., Panjabi, A., Helft, L., Parr, M., and Marra, P. P. (2019). Decline of the North American avifauna. Science, 366(6461), 120–124. https://doi.org/10.1126/science.aaw1313

Saito, E. K., Sileo, L., Green, D. E., Meteyer, C. U., McLaughlin, G. S., Converse, K. A., and Docherty, D. E. (2007). Raptor mortality due to West Nile virus in the United States, 2002. Journal of Wildlife Diseases, 43(2), 206–213. https://doi.org/10.7589/0090-3558-43.2.206

Smith, K. G., S. R. Wittenberg, R. B. Macwhirter, and K. L. Bildstein (2020). Northern Harrier (Circus hudsonius), version 1.0. In Birds of the World (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.norhar2.01

USFWS. 2014. Species Status Assessment for Species Osprey (Pandion haliaetus).

U.S. Fish and Wildlife Service. 2021. Birds of Conservation Concern 2021. United States Department of the Interior, U.S. Fish and Wildlife Service, Migratory Birds, Falls Church, Virginia. http://www.fws.gov/birds/management/ managed-species/birds-of-conservation-concern.php

Vidaña, B., Busquets, N., Napp, S., Pérez-Ramírez, E., Jiménez-Clavero, M. Á., and Johnson, N. (2020). The role of birds of prey in West Nile virus epidemiology. Vaccines, 8(3), 550. https://doi.org/10.3390/vaccines8030550

Wilsey, C., Taylor, L., Bateman, B., Jensen, C., Michel, N., Panjabi, A., and Langham, G. (2019). Climate policy action needed to reduce vulnerability of conservation‐Reliant Grassland Birds in North America. Conservation Science and Practice, 1(4). https://doi.org/10.1111/csp2.21

Partners in Flight, Vanishing Habitats. https://partnersinflight.org/vanishing-habitats/

Learn more about this species natural history at All About Birds or at Hawk Mountain’s website.