A male bison, reportedly weighing 2,000 pounds (900 kg), ran at an elderly man, butted him with his head and threw him into the air in Wyoming’s Yellowstone National Park.

Viral footage of the incident shows a boy and his grandfather taking a photograph of the bison as it lies in the grass, before the huge animal jumps to its feet and chases them.

The man, identified by US media as 65-year-old Carl Isom-McDaniel, suffered multiple injuries and was described by witnesses as “being in a lot of pain.”

He was sent to the hospital, according to the New York Times. The National Park Service (NPS) has not released any information about the attack.

The BBC has asked the NPS for comment.

“The bison may seem calm, but these large animals have injured more people in Yellowstone than any other animal,” the organization states on its website.

“They can run 3 times faster than humans, so it is very important to give them plenty of space.”

The NPS advises visitors to Yellowstone to stay at least 25 yards (23 meters) from bison at all times and to “never approach a bison to take a photo.”

The incident occurred Friday night at Bridge Bay Campground near Yellowstone Lake in the last hour before sunset.

Isom-McDaniel and her grandson appear a good distance away from the animal as their walk stops and they raise their cameras to take a photo.

The bison then repeatedly drops to its side in an agitated manner before leaping to its feet.

A white truck slowly approaches the scene, but after the bison charges the truck, the driver speeds up. The animal continues to move forward, leaving a cloud of dirt in its wake as it runs toward Isom-McDaniel and her grandson.

The pair try to evade the bison by running through a thicket of trees, but the animal eventually caught Isom-McDaniel.

“The bison hooked him with his left horn on the hip and threw him into the air,” Mike Macleod, who recorded the incident, told local newspaper Cowboy State Daily. “He made a perfect turn and landed on his side.”

Mcleod continued: “His leg hurt a lot and otherwise he was conscious the whole time, in good spirits, joking around.”

Summer is the busiest season in Yellowstone, according to the NPS. Almost 60% of annual visits occur only during the months of June, July and August.

July overlaps with the animal’s mating season, the “peak breeding” period where testosterone levels among bulls rise, said Jennifer Barfield, science leader for Colorado’s Laramie Foothills Bison Conservation Herd.

“That will really drive their behavior and they will be potentially more unpredictable than other times of the year,” the Colorado State University professor said.

Barfield said his team stays away from bison during mating season, except when conducting observations from the safety of a vehicle.

For those on foot, he said, “It’s always good to keep in mind that 25 yards is a minimum distance for safety.”