Bats Get to Keep Their Bridge, and That Must Make Their Day

The demolition of a bridge in Orange County’s backcountry where more than 1,500 bats have roosted has been postponed so the mostly female -- and pregnant -- bat colony can continue to use the span as a maternity ward.

Knocking down the bridge, activists said, would have disrupted and perhaps killed hundreds of young bats that had settled in the dark hollows under the structure.

“A disaster has been postponed, at least for now,” said Stephanie Remington, a biologist who helped rally opposition.

Score one for the Mexican free-tailed bats, whose habitat not only in Southern California but throughout the United States has eroded as people have pushed into wild lands.

In recent years, conservationists have pushed for the preservation of bridges and old mine shafts colonized by bats.

In such cities as Austin, Texas, preserved bat enclaves have become tourist attractions. Such success stories have been rare in Southern California.

The Orange County bridge was built eight years ago by an Alabama-based firm so that its trucks hauling sediment from a dredging project could cross over busy Santiago Canyon Road.

The plan was to remove the bridge June 1, a job that has been pushed back to October -- when the bats will have migrated to Mexico.

Fearing the bats will return next mating season and discover that their home has been removed, environmentalists hope to keep the bridge intact. The colony is believed to be the county’s largest.

Supervisor Bill Campbell, who has received dozens of calls and e-mails about the bats, said much of the concern focused on their maternal season, which runs from April through the fall. When temperatures drop, the flying mammals migrate to Mexico’s northern states for the winter.

Bat pups are born deaf, blind and without fur. They rely on their mothers for food and lessons on flying and hunting insects. The thought of destroying hundreds of pups by demolishing the bridge alarmed Remington, who said she found support from Campbell, the contractor who built the bridge, the Irvine Co., which owns surrounding land, and environmentalists.

“We’re thinking about relocating the bats or saving the bridge and incorporating it as part of the county’s network of trails,” said Campbell.

As for the male bats, they have little to do with raising the young. After mating, they fly off to roost alone, sometimes on outer areas of colonies or with other males.

According to experts, the bats prefer caves, but bridges make perfect habitats too. The Orange County bats are mostly Mexican free-tailed but also include some smaller, Yuma bats.

While conservationists would prefer that the bridge remain, experts say another option is to build a giant bat house. Other ideas include installing PVC tubes or special netting that allow the bats to fly out but not in, an eviction process of sorts, and one that would force the bats to take up shelter elsewhere.

“Bats return each year to the place where they were born,” Remington said. “There’s no guarantee they will move into a new bat house, so we think the best option is to try and keep the bridge as part of the trails system.”

Mexican free-tailed bats weigh less than half an ounce, and have a 12-inch wingspan. Their ears are wide and set apart to help them find prey using echolocation.

Mexican free-tailed bats consume mosquitoes, flies, moths, midges, cucumber beetles, stink bugs and other insects.

“They are good for farmers because they eat insects that attack crops,” said Rachael Long, a UC Davis wildlife biologist in pest management.

Mexican free-tailed bat populations have fallen because of pesticide use and cave destruction. The bats live in caves not only in Mexico and the United States but in Central America, the West Indies, central Chile and Argentina.

One of the largest colonies is north of San Antonio, at Bracken Cave, which has nearly 20 million bats. The colony can eat as much as 250 tons of insects a night.

In Austin, Mexican free-tailed bats have won a public relations war that once had them confused with their nasty cousins, vampire bats. Now, schools, scouting groups and other organizations help with an awareness campaign that has made the bats more popular.

“Many bridges have been modified intentionally to make them bat-friendly because bats bring tourists,” said Barbara French, conservation officer with the Austin-based Bat Conservation International. “Our colony brings $8 million in tourist revenue to Austin a year.”

Hotels in Austin market rooms that face the city’s famous Congress Avenue Bridge so tourists can watch a colony of about 1.5 million bats take flight as night settles in. Each evening from March to early November the bats emerge from under the bridge and fly off in spectacular “dark moving ribbons” that cross the sky, French said.

The Orange County colony is small but helpful to local farmers, said Remington. She estimates the colony consumes 20 to 30 pounds of insects a night.

Remington doesn’t know when the colony moved in, but she has been studying it for about five years. She carries sophisticated listening devices that allow her to hear the echolocation, which comes out “as a series of clicks,” she said.

It’s difficult to see the bats during the day. They like crevices, sometimes squeezing into spaces less than an inch wide, and find any surface that allows them to hang by their claws.

At the Santiago Canyon bridge, they found a seam barely 4 inches wide to call home. They prefer the bridge’s warmer west side, which stays in the bats’ comfort zone of 80 to 100 degrees.

The tell-tale signature isn’t found by looking up. Remington instructs viewers to check the ground for guano, or bat droppings.

“I can stand silently near this bridge just before dusk and they know that I’m here. I don’t know how they know. It’s either they can smell me or detect me but I don’t know which,” Remington said. “They’re my hobby. They’re just fascinating.”