(MARBLE CANYON, AZ (Associated Press) — Three California condors have died from avian flu in northern Arizona and authorities are trying to determine what killed five others in the flock.

The National Park Service on Friday said the birds that died last month tested positive for Highly Pathogenic Avian Influenza.

The giant endangered vultures all were in a flock that flies throughout northern Arizona and southern Utah.

The virus hasn’t been detected in other populations in California or Mexico’s Baja California.

The California condor is one of the world’s largest birds with a wingspan of up to 10 feet. It was nearly extinct by the 1970s but there are more than 300 in the wild now thanks to a captive breeding program.