Rangers at Yellowstone National Park euthanized a baby bison that tourists had brought to it a ranger station because they thought the animal was cold.

The Rangers ticketed a pair of tourists and tried to return the baby bison to spot where it had been picked up.

Karen Richardson, who was chaperoning a group of fifth-graders on a field trip, saw a father and son pull up at a ranger station with the baby bison in their SUV.

“They were demanding to speak with a ranger,” Karen Richardson told EastIdahoNews.com. “They were seriously worried that the calf was freezing and dying.”

Rob Heusevelet, one of the students’ father, said he told the men to remove the animal from their car and warned they could be in trouble.

“They didn’t care,” said Heusevelt. “They sincerely thought they were doing a service and helping that calf by trying to save it from the cold.”

Rangers arrived and ticketed the father-son tourists, who were visiting from another country. The rangers followed the tourists back to where they picked up the calf, and the animal was released.

In a prepared statement, the Park Service said the animal had to be euthanized after repeated efforts to have the herd accept it. The baby bison then continued to approach vehicles. It was put down for safety reasons, the Park Service said.

Last week in Yellowstone National Park, visitors were cited for placing a newborn bison calf in their vehicle and transporting it to a park facility because of their misplaced concern for the animal's welfare. In terms of human safety, this was a dangerous activity because adult animals are very protective of their young and will act aggressively to defend them. In addition, interference by people can cause mothers to reject their offspring. In this case, park rangers tried repeatedly to reunite the newborn bison calf with the herd. These efforts failed. The bison calf was later euthanized because it was abandoned and causing a dangerous situation by continually approaching people and cars along the roadway.

Tourists are required to stay at least 100 yards away from bears and wolves and at least 25 yards from other large animals, including bison, according to the National Park Service. Bison injure more humans than any other animal in the park.