A newborn bison calf that was put in the back of a car by visitors to Yellowstone National Park who thought it was cold had to be put down after the animal's mother rejected it when it was returned to the herd.

Park wardens condemned the stupidity of the tourists, describing it as "inappropriate, dangerous and illegal behavior" that puts animals and humans at risk.

The bison was euthanised because it was abandoned and causing a "dangerous situation" by continually approaching people and cars in the park, officials added.

The incident is the latest in series of similar interferences:

Tourists visiting Yellowstone are asked to stay at least 25 meters away from bison and to stay even further away from creatures such as bears and wolves.

Almost 5000 bison, also known as buffalo, roam freely throughout Yellowstone and are a major attraction for the millions of American and international tourists who annually flock to the park that spans parts of Wyoming, Montana and Idaho.