Rough-legged Hawks at Risk
Rough-legged Hawk Image by Bill Moses
Rough-legged Hawk
(Buteo lagopus)
Although Rough-legged Hawk populations appear stable in the Northwest and Western regions of their range, the East and Northeastern Regions are showing a different story. For Rough-legged Hawks, 43% of 21 sites continent-wide showing declines from 2009-2019, and all of the reported declines were located within the Central and Eastern regions of the population assessment. Over the last twenty years, a mix of stable and declining count trends with the majority of declines located in the East region while the West remained stable. CBC trends for the last decade indicate winter declines throughout the US except for some Northwestern and North Central states and provinces where some increases were observed. The regional pockets of CBC increases may indicate short-stopping, but that is likely not the case in the East, where declines are observed both during migration and during wintering surveys. Those declines likely represent an actual population decline. Additional research is needed to determine the causes for these declines to proceed with management recommendations.
Global Conservation Status:
IUCN 06/08/2021 – Least Concern (LC)
U.S. and Canada Conservation Status: Critically imperiled in 3/66 states and provinces (ON, DC, VA). Imperiled in 5/66 states and provinces (MB, NF, PE, MD, ME). Vulnerable in 15/66 states and provinces. Apparently secure in 19/66 states and provinces. Secure in 7/66 states and provinces.
Rough-legged Hawk Population Status by State and Province in the US and Canada
The data used in this figure are listed above. These data were compiled from NatureServe and the U.S. Fish and Wildlife Service.
Birds of Conservation Concern List:
Not listed. The species is protected by the Migratory Bird Treaty Act (MBTA)
Range:
As far north as Baffin Island and throughout the Canadian Arctic and Alaska for breeding and down south to California, Southern Texas, and Northern Kentucky for wintering.
Habitat:
Tundra, mainly treeless, some wooded tundra, and extreme north taiga. In winter, often more areas modified by humans such as pastures, hayfields, croplands. Also prairies, marshes, and shrublands. Nests on rock cliff faces.
When Did Rough-legged Hawk Migration Counts Begin Declining?
The count site that observed the highest count of Rough-legged Hawks with an average of 551 individuals each fall, Hawk Ridge, Minnesota, was stable in the 1990s and through 2010 but began to observe declines starting in 2013. The count site to observe the second highest average migration count of Rough-legged Hawks over the last decade with an average of 345 individuals each spring in Whitefish Point, Michigan, has observed decreasing counts since the site began collecting migration data in 1980. The counts at this site began to plateau between 1990 to 2004 but again began observing declines through to present. From 2009 to 2019 their counts were stable, although that may be owed to two of the years having increased counts which were possibly due to the species’ irruptive behavior (Paprocki et al., 2015). Unfortunately, migration data from this site before the 1980s is not available for this species, however most sites that have data from the 1980s to present reveal declining trends.
RPI Trend Maps:
These maps summarize the latest RPI trend analyses for count sites throughout North America.
Figure 2. Summary map of RPI and CBC trends from 2009 to 2019 for Rough-legged Hawks.
Find the interactive version of the Christmas Bird Count (CBC) maps here.
BBS: No data
Why are Rough-legged Hawk Migration Counts Declining?
Rough-legged Hawks have not been studied enough to determine the cause of the apparent declines in migration and wintering survey data. Their irruptive behavior, which likely coincides with arctic lemming irruption, makes migration and wintering data challenging to interpret. The increase in Christmas Bird Count numbers in the Central region suggests a northward shift in winter range or short-stopping, which involves individuals not migrating as far south, or a decrease in the proportion of individuals in populations that migrate at all. Short-stopping and winter range shifts are likely linked to a combination of warmer temperatures, increased food resources, and more suitable, undisturbed habitat availability further north (Paprocki et al, 2015). However, this does not explain the declines observed in both the Christmas Bird Count and migration counts in RPI’s Eastern region and the Christmas Bird Count declines in the West where RPI migration count data appears stable. The species is likely threatened on it’s wintering and nesting grounds, where it prefers to use meadows and marshes that are not grazed by livestock. Some causes for mortality during wintering that have been observed include collision, electrocution, and shooting, but the extent to which each of these effects the Rough-legged Hawk population is unknown. West Nile virus has increased in Canada and the Northeastern United States. Rough-legged Hawks are vulnerable to the virus, which can result in mortality (Saito et al., 2007). Recent increases in wildfire frequency and intensity may also impact Western populations.
Threats
Loss of Habitat
Habitat loss may impact Rough-legged Hawks both on nesting and wintering grounds. Tundra nesting habitat is undergoing rapid change. Grasslands, prairie, and agricultural wintering habitats for Rough-legged Hawks are vulnerable, although Rough-legged Hawks have been shown to prefer wildlife refuges over agricultural use land (Root, 1988).
Climate Change
A 2022 study found a positive correlation between Rough-legged Hawk annual breeding population variability and climatic severity. Increased rainfall, insects, and other changes in tundra may be affecting nest success. The impact of the overall increase in both number of wildfires and fire severity in Western North America on raptor populations also requires further investigation. These changes can result in profound changes in Rough-legged Hawk wintering habitat, including vegetation shifts, invasive species, and a decrease in biodiversity. Some preliminary research has shown raptors may not use nesting habitat after a fire, which suggests raptors have experienced further declines in usable habitat due to increased fires in the West (Gao, 2020).
Vehicle Collisions
It is estimated that highway mortality may be the biggest mortality factor on Rough-legged Hawk wintering grounds, especially in the Great Basin region of the United States. Of 48 banding recoveries throughout their wintering range from 1955-1979, 29% were road kills. A study done from 1980 to 2000 showed that total vehicle miles traveled in the United States grew 80% and the number of vehicles per 1000 people rose 14% (Polzin, 2017).
Irruptive Prey Cycles
Rough-legged Hawks primarily feed on small mammals which make up 80% of their diets; lemmings and voles during breeding season and voles, mice, and shrews during wintering. Lemming abundance in the arctic follows an irruptive cycle, which may result in an irruptive migratory pattern in Rough-legged Hawks. They can also take small birds such as buntings, grouse, waders, and other waterbirds.
Infectious Disease
West Nile virus (WNV) first reached the United States in New York in 1999 and has since spread across the continent. The primary vectors for WNV are mosquito species Culex restuans and Culex pipiens, and many avian species serve as reservoirs. Rough-legged Hawks are infected with WNV through a mosquito bite or through feeding on infected birds (Vidaña et al., 2020). Rough-legged Hawks infected with the virus can present neurologic symptoms and mortality. From 1991 to 2014, 5% of the deceased Rough-legged Hawks submitted to the Ontario/Nunavut node of the Canadian Wildlife Health Cooperative were infected with the virus (CWHC; Smith et al., 2018). Declines in the Northeastern US might be partially related to WNV prevalence in the region, although Rough-legged Hawk migration and wintering trends were declining in the region before its introduction (Bolgiano, 2019). Rough-legged hawks are most commonly infected with WNV through a mosquito bite or through feeding on infected birds (Vidaña et al., 2020). More research is needed to determine the extent to which WNV has impacted raptor populations, including Rough-legged Hawks.
Written by Rebekah Smith
Literature Cited
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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.
