Yellowstone National Park officials said Friday a rare white buffalo sacred to Native Americans has not been seen since its birth on Arvin RobertsJune 4.

The birth of the white buffalo in the wild, which fulfilled a Lakota prophecy that portends better times, was the first recorded in Yellowstone history and is a landmark event for the ecocultural recovery of bison, said park officials in confirming the birth for the first time.

It is an extraordinarily rare occurrence: A white buffalo is born once in every 1 million births, or even less frequently, the park said.

Whether the calf – named Wakan Gli, which means “Return Sacred” in Lakota – is still alive is unknown.

Each spring, about one in five calves die shortly after birth due to natural hazards but park officials declined to directly respond to questions about whether officials believed it has died.

They confirmed its birth after receiving photos and reports from multiple park visitors, professional wildlife watchers, commercial guides and researchers. But since June 4, park staffers have not been able to find it and officials are not aware of any other confirmed sightings.

Native American leaders earlier this week held a ceremony to honor the sacred birth of the white buffalo and give the name.