After a surge in bison-related injuries last summer at Yellowstone National Park, a case review points to smartphone photography as a culprit.

All five people who were injured by bison from May to July 2015 failed to maintain the required 75-foot distance from the animal, and three sustained injuries while taking photographs from 3 to 6 feet away, including two who turned their back on the bison to take the picture. One admitted to taking a selfie.

Bison encounters related to photography are nothing new, as 10 of 35 incidents between 1980 and 1999 involved people with cameras. But most of those people were at least 10 feet from the bison.

“The popularity of smartphone photography with its limited zoom capacity and social media sharing of selfies might explain why visitors disregard park regulations and approach wildlife more closely than when traditional camera technology was used,” the Centers for Disease Control and Prevention wrote in the most recent edition of its “Morbidity and Mortality Weekly Report.”

The report notes that smartphones now meet the needs of most casual photographers, who like the ability to share photos and videos with their phones.

After 33 bison-related injuries were reporting from 1983 to 1985, the park implemented education and outreach campaigns to reduce occurrences. It appeared to be successful, as less than one bison-related injury per year was reported between 2010 and 2014. The spike last summer led to a review to inform future prevention efforts.

In other notes from the review, all of the 2015 incidents occurred in a developed area, such as a hiking trail or geyser basin. Four injuries occurred when three or more people approached the bison. Two people were gored, and three were tossed into the air. Four required hospitalization, three of whom were transported by helicopter ambulance. There were no deaths.

Per Yellowstone policies, wildlife should not be approached, regardless of how tame or calm they appear. When an animal is near a trail, boardwalk, parking lot, or in a developed area, visitors must give it a wide berth and not approach it closer than the required minimum distances: 75 feet away from all large animals – bison, elk, bighorn sheep, deer, moose, and coyotes – and at least 300 feet away from bears and wolves.

Bison can run three times faster than humans can sprint and are unpredictable and dangerous. Visitors are advised to give the animals enough space and alter their plans to avoid interacting with an animal in close proximity.