SALT LAKE CITY (AP) — Visitors to Zion National Park in southern Utah are being asked to be on alert for something besides dramatic red rock vistas: Coughing bighorn sheep.

Excessive coughing is a symptom of pneumonia, which can be deadly to the animals, and wildlife officials are trying to determine how much the sickness has spread, said Zion spokeswoman Aly Baltrus. About 500 bighorn sheep in a herd of 800 from the area live on slick rock areas on the east side of the park, Baltrus said.

Two bighorn sheep have already been killed in recent weeks to diagnose the illness after a female, or ewe, was found with the cough on July 20, she said. Zion officials are asking visitors to report where they hear the coughing so park biologists can track the illness.

About 25,000 people visit the park daily during July. The pneumonia the bighorn sheep suffer isn't dangerous to humans.

"You can hear it from a distance," Baltrus said. "It's very much like a human cough."

Pneumonia is fairly common in bighorn sheep herds and the animals can often fight through the sickness and survive, but some strains can be deadly, said Jace Taylor, a bighorn sheep biologist with the Utah Division of Wildlife Resources.

Hundreds of bighorn sheep in Nevada, Montana, Utah and Washington died or were killed by wildlife officials in 2010 in one of the deadliest pneumonia outbreaks on record, Taylor said.

The sickness is easily passed among the animals, such as nose-to-nose touching or when one bighorn sheep coughs on another, Taylor said.

This if the first time pneumonia has been detected in the Zion herd, Baltrus said. She said it's difficult to contain spreading now because males are beginning to roam and look for mates.

"We're definitely concerned," Taylor said.