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Yellowstone National Park officials euthanized a bison calf after tourists put the newborn in their car and caused the animal to be rejected by its herd, the park said Monday.

Criminal charges against the tourists, who the park did not identify, are pending.

Rangers repeatedly tried to reunite the calf with its herd, according to a statement released by the park. The efforts failed, and the calf was later euthanized because it was abandoned and approaching people and cars along the road.

Human interference can cause mothers to reject their offspring, the park said.

Yellowstone released a statement Monday after receiving criticism for euthanizing the calf. In order for the calf to leave the park, it would have had to spend months in quarantine to be monitored for brucellosis. No approved quarantine facilities exist, and the park said it doesn't have the capacity to care for a calf that's too young to forage on its own.

"Nor is it the mission of the National Park Service to rescue animals: our goal is to maintain the ecological processes of Yellowstone," the statement said. "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."