A bison calf snatched by – and recovered from – tourists who thought they were "saving" him from the cold has now been euthanised by the US National Park Service, it was reported on 17 May.

Officials said the calf was rejected by its mother and herd when park workers returned him to his home territory. They had taken the calf away from a father and son visiting Yellowstone National Park, who thought the calf was suffering in the low temperatures and loaded him up into their SUV.

Once shunned by his herd, the lonely calf repeatedly approached people and cars along the roadway, creating what officials described as a safety hazard, according to a Yellowstone Park Service statement. After repeated failed attempts to unite the calf and his mother, the bison was eventually euthanised.

The pubic was furious about the killing and several people commented angrily about the death on the park service's Facebook page. They demanded to know why the calf had not been adopted out to a facility that could care for it.

However, park service officials explained in the statement that the calf would have had to undergo months of quarantine to be monitored for the highly contagious disease brucellosis.

"No approved quarantine facilities exist at this time, and we don't have the capacity to care for a calf that's too young to forage on its own," the statement said. "Nor is it the mission of the National Park Service to rescue animals. Our goal is to maintain the ecological processes of Yellowstone. Even though humans were involved in this case, it is not uncommon for bison, especially young mothers, to lose or abandon their calves. Those animals typically die of starvation or predation."

Officials said the tourists' decision to haul the calf out of the park in an SUV was the absolute wrong thing to do to begin with, and immediately put the calf at risk of rejection by its mother.

Park visitors have been increasingly engaging in inappropriate, dangerous, and illegal behaviour wildlife officials complained, warning the public to leave America's new national mammal alone.

The father and son duo who snatched the bison calf were ticketed for taking the animal. They were apprehended when they showed up at a ranger station with the animal in their vehicle.