YELLOWSTONE NATIONAL PARK — A new study shows bison in Yellowstone National Park are more than twice as likely to injure visitors as grizzly bears, leading park officials to consider a rule requiring visitors to stay at least 100 yards away from bison.
Bison have charged people 81 times since 1978, resulting in injuries ranging from goring puncture wounds to broken bones to simple bruises and abrasions, according to a list compiled by Yellowstone volunteers Jim and Edna Caslick.
Grizzly bears have injured 30 people since 1978. Grizzly bears have killed two people since 1978; bison have killed two people since 1971.
"We've always known that bison hurt more people than bears, but I didn't know they hurt as many more people as they do," said park biologist Tom Olliff, who oversaw the study.
The figures emerged as the Caslicks pored through case reports from park rangers about encounters between visitors and wildlife besides bears. They found bison to be the most dangerous park species in terms of injuries.
The high number may be due to a perception of bison as harmless, biologists said.
"I think when they see a bear out there, they're less likely to approach it than they are a bison, which they sort of treat like a big domestic cow," said Yellowstone grizzly-bear biologist Kerry Gunther.
Park records bear that out. In the 35 bison-human run-ins where rangers recorded the distance between the person and the bison, the person was an average of 28.5 feet away from the bison, well below the minimum required distance of 75 feet.
Six people were within 10 feet of bison when the animals charged. Two others were attempting to pet or feed a bison and two were throwing rocks or sticks at bison in misguided attempts to shepherd an animal into their photograph.
All the bison charges appeared to be defensive reactions to people who approached them too closely. A few of the charges may have been triggered when people walked up on bison without realizing it.
"The common denominator in all the cases is the close distance," Olliff said. "People don't understand that bison can be dangerous. They don't look dangerous, but they are amazingly quick and amazingly agile when they want to be." After a surge of bison gorings in the 1980s, rangers began distributing extra warning fliers to visitors at entrance gates. The number of run-ins has dropped since then, but bison still charge an average of five people each year, compared to an average of one bear-caused injury per year.
Visitors must now stay at least 100 yards from bears, but only 25 yards from bison, elk, bighorn sheep and most other park wildlife. The Caslicks recommended that park officials change the rules to require a 100-yard minimum distance from bison.
Olliff said park officials are considering the change, although it would not go into effect until next year at the earliest. He noted that bison often roam close enough to roads and trails that it might not always be practical for people to stay 100 yards away, but he said such a rule would give law enforcement rangers the legal leverage to warn people away.