Yellowstone National Park is comprised of 3,472 mi2 (8991 km2), or 2,221,766 acres. The park’s boundaries lie 96% in the state of Wyoming, 3% in Montana and 1% in Idaho. Yellowstone has five park entrances, leading to 466 miles of road (310 miles paved). Less than 1% of Yellowstone’s landscape is covered by roads. In Yellowstone, there are approximately 150 (conservative) grizzly bears whose home ranges are completely, or partially inside of the park.
Some areas of the park, roadways run through highly desired and preferred grizzly bear habitat. Some bears become habituated to human-presence by hanging along the roadsides. Habituation can be defined as when bears become accustomed and experience no threat from human activity consistently and frequently, they begin to expect the same pattern time and time again, and react with very little response (Knight and Cole 1995). Habituation is not always a terrible thing, especially with grizzly bears. Habituation will allow bears to use areas with high human presence and activity, which has been demonstrated to increase habitat effectiveness (Herrero et al. 2005). In Yellowstone, this sort of behavior is commonly observed, where some wildlife, and bears may be subject to seeing thousands, if not millions of visitors each year and over the course of their lifetime. In this sort of environment, bears will adapt and acclimate to the presence and activities of visitors if seen at a great enough frequency. Yellowstone and Grand Teton National Park’s beginning in the 1990’s shifted their focus from managing the bears, to managing the people. Instead of trapping, relocating, and hazing bears, park staff began to ensure that visitors were in compliance at bear jams and exhibiting predictable behavior. This strategy has been in place for 25 years (1990-2014) (Gunther et al. 2015). Over the past quarter century, both Yellowstone and Grand Teton have experience increasing levels of bear habituation in roadside habitats, leading to an increase in “bear-jams” (Haroldson & Gunther 2013).
However, while habituation allows an increase in habitat effectiveness and allows for satisfying visitor experience, it does create a dangerous and unbeknownst situation for the wildlife, a double-edged sword. Bears and cars don’t mix typically. If bears become habituated, it can pose a risk for vehicle accidents. Habituation may not always be the case for grizzly presence near the roadways. Transient bears may use the roadways as a travel corridor, or even crossing to get from place to place. Sometimes after emerging from hibernation, bears may use the roads in an effort to conserve energy expenditure when snow is still deep (same with other wildlife such as bison).
Between 2009 and 2018, 25 grizzly bears were documented road-kill mortalities by the Interagency Grizzly Bear Study Team (IGBST) in the Greater Yellowstone Ecosystem (GYE). Of the 25 bears, 19 were male, 5 were female and 1 was unknown; 11 were subadults, 4 were yearlings, 3 cubs-of-the-year (COY), 6 adults, and 1 unknown. In Grand Teton National Park (GTNP) 4 grizzlies were documented and in Yellowstone National Park 4 grizzlies were documented. Outside of the national parks, 8 grizzlies were documented roadkill mortalities in Montana, 8 in Wyoming and 1 in Idaho. The IGBST reports that 80% of grizzly bear mortalities are human-caused. This includes but not limited to: roadkill, natural death, defense of life and property (DLP), hunting, mistaken identity (black bear hunt). From 2009 until 2018, 429 grizzlies have been documented mortalities, of which roadkill mortality accounts for approximately 6%. The other 94% consist of DLP, natural, hunting, mistaken identity. As visitation increases, it is likely (anecdotal) that roadkill mortalities may increase. More grizzlies on average are killed every year as a result of self-defense while hunting than motor vehicle accidents; this was the case between 2009-2018 (IGBST Annual Morality Reports 2009-2018)
Ultimately, roadkill mortalities do not always fall back on motor vehicle operators. Instances have occurred, where a motor vehicle operator was doing everything correctly, and a bear darted in front of their vehicle. In rare cases, bears have even timed their crossing incorrectly and run into vehicles. Between 1989 and 1999, it was found that bears (grizzlies and black bears) were killed on roads with higher speed limits (Gunther & Biel 1999). It is important to note that it is not always the fault of the vehicle operator. While unfortunate, sometimes bears are unpredictable, and run across the roadway from thick brush or timber, allowing for little time to react. Chastising visitors involved in accidents which are out of their control is irresponsible. Focusing on inattentive and negligent operation of motor vehicles is a more beneficial initiative. Striking and killing a grizzly bear in YNP is rare, though, this does not mean it cannot happen.
Another important consideration: not all bears struck and hit by vehicles die. It is a poor assumption that all bears involved in motor vehicle accidents perish. In recent years, bears have been struck by vehicles, later running off into the wilderness with minimal notable or documented injuries.
Ex: 2002 -> grizzly bear #125, accompanied by 2 COY, was struck by a vehicle just north of Canyon Junction in YNP, causing her collar to drop; the severity of her injuries was unknown at the time. Four years later in 2006, she was alive and well, captured and collared again at Antelope Creek in YNP.
2010 -> Mary Mountain Trailhead, Hayden Valley, YNP: a female grizzly with 3 cubs was struck during late May; Bear Management closed Mary Mountain Trail temporarily and investigated, but found no signs of a mortality.
Ultimately, when traveling on roads in YNP and GTNP, be conscientious of your surroundings. Sometimes, the beauty of the landscape, or even nearby wildlife may blind us from focusing our attention on the road while driving. Sometimes, we may occasionally find ourselves speeding. Ultimately, it is the role and responsibility of every visitor and motor vehicle operator to maintain complete control of your vehicle at all times. It is also your responsibility to inform park officials, or local fish & game authorities of wildlife/vehicle injuries and related accidents.
Tyler Brasington is a native born and raised Pennsylvanian, yet proud current Wisconsin resident. He graduated from the University of Wisconsin-Whitewater with a B.S. in Environmental Science. Currently, Tyler is pursuing his masters in Natural Resources with the University of Wisconsin-Stevens Point. He has worked in Yellowstone National Park under the guidance and supervision of Dr. George Clokey and Dr. Jim Halfpenny.
Disclaimer: The information and views expressed on this page do not necessarily represent the views of the Department of Interior, US Geological Survey, National Park Service or the United States Government.
The Greater Yellowstone Grizzly Project
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