Fire Scorches Regional Park : Environment: Officials are investigating the blaze at the Costa Mesa preserve, home to endangered species and an unknown number of transients.

A fire burned for nearly seven hours in a dense, county-owned nature preserve, which is home to both endangered species and transients, before firefighters controlled it Wednesday morning.

The fire burned in 10 of the 154 acres of the nature preserve in Talbert Regional Park, just north of 19th Street in Costa Mesa.

The preserve has 142 species of migratory and indigenous birds, including the endangered Belding’s savannah sparrow and the least tern, said Jonathan Schiesel, a Costa Mesa resident who heads the Friends of Talbert Park. Schiesel and firefighters said they did not know the extent of damage to the birds or their habitat.

The preserve also has an unknown number of camps set up illegally by transients, said Larry Paul, a spokesman for the county Environmental Management Agency.

After the fire began at 11:15 p.m. Tuesday, firefighters in a helicopter warned the transients to evacuate.

Fire officials are still investigating the cause of the blaze. They suspect a campfire started by transients or children playing in the brush, said Battalion Chief Judy Jewell of the Costa Mesa Fire Department.

Sixty firefighters from the Costa Mesa and Orange County fire departments fought the blaze, but the preserve’s tall, dense pampas grass and groves of arroyo willow trees made it difficult for them to reach the area, and the grass caused flames to spread quickly.

Cool temperatures and light morning drizzle did help to contain the fire, but hot spots remained into the early afternoon Wednesday, Jewell said.

Most of the willow groves were spared, while the pampas grass, which is not indigenous to the area, burned quickly. The damage was not extensive, Paul said. In fact, occasional fires are natural in the wilderness and may actually restore nutrients to the soil, he said.

After the fire was contained, firefighters took special care in handling valuable willow groves during the cleanup, he said.

“The fire officers responding were aware of the environmental sensitivity of the area,” Paul said. “They called me during the middle of the night because of the working relationship we’ve had with them and to know what kinds of things they should be concerned with.”

The agency has held meetings with the Costa Mesa Fire Department in the past two years to prepare for emergencies such as this one, Paul said.

One Costa Mesa firefighter, Capt. Brian Roberts, was treated at Hoag Memorial Hospital Presbyterian in Newport Beach for smoke inhalation and released. No other injuries were reported.