Homes for the Fly-by-Night Crowd : Bats: Boy Scouts nail roosting boxes to trees to help the much-maligned mammal find proper housing.

Where does a bat go if there is no belfry?

A U.S. Forest Service biologist and a Boy Scout think that they have the answer. Responding to a shrinking supply of quality roosts for the local bat population, the biologist and the Boy Scout have teamed up to provide one of nature’s most misunderstood creatures with artificial roosts in Angeles National Forest. They call them bat houses.

Brandon Forbes, a 17-year-old senior at Sylmar High School, supervised the building of 20 of the boxlike wooden houses as part of his Eagle Scout project. On Saturday, he and fellow scouts from Troop 150 nailed 10 of the houses to trees in Little Tujunga Canyon of Angeles National Forest above Sylmar, launching what is apparently the only organized bat house project in California.

The project is the brainchild of wildlife biologist Sabrina Keen, who will install the other 10 shelters on the sides of Forest Service buildings throughout the San Gabriel Mountains. She plans to monitor all 20 for years.

All this effort aims to address a growing concern among biologists about the destruction of bat habitat in Southern California by development. Scientists believe that the flying mammals’ numbers are declining, but they admit that firm estimates of the local bat population do not exist.

“We don’t have a lot of people out there counting bats,” said Lynn Barkley, a bat expert who is also a collections manager for mammalogy at the Los Angeles County Museum of Natural History.

Bats roost in, among other things, caves, hollow trees, rock overhangs, old buildings, eaves and attics. But many of their favorite haunts, including belfries, are rare these days.

“A lot of modern architecture doesn’t lend itself to bat roosts,” Barkley said. Wooden bridges, a favorite bat roosting place, have been replaced with concrete over the years.

Bats have also been driven out of many places they would like to call home. Last summer in Monrovia, where bats had roosted for many years, residents fearing rabies embarked on a massive bat removal campaign, boarding up the attics of several turn-of-the-century houses.

To aid such displaced bats, Keen wants to enhance the known bat habitat in the forest. “I’m hoping to give them a safe place to roost, a safe place for a nursery,” Keen said.

Bats in California are insectivores, and pesticides may be taking their toll on the bat population as well, Barkley said.

Although bats live a long time, up to 20 years, they have a low birth rate, typically producing only one offspring a year after a nine-month gestation period, Barkley said. “So they can’t reproduce and build up in numbers like rodents can,” she said.

There are 950 species of bats worldwide and 26 species in California, making it second only to Texas, which boasts 36 species.

The two most likely tenants for the Little Tujunga Canyon bat houses are the big brown bat and the Mexican, or Brazilian, free-tailed bat, the two most common local species.

The big brown bat, or Eptesicus fuscus , is 3 1/2 to 5 inches in length and has a wingspan of 10 to 13 inches, relatively large for a bat. The free-tailed bat, Tadarido brasiliensis , is a bit smaller at 3 1/2 to 4 inches in length.

Although Barkley said she has heard of individuals purchasing mass-produced bat houses for their yards, she had never heard of an organized bat house project in California. Bat houses are common in Texas, she said, especially in Austin, regarded as the bat capital of the United States and home of Bat Conservation International, a private group of bat preservationists.

The bat houses erected Saturday are narrow boxes standing three feet high, with entryways at the bottom. Partitions inside the box create five separate roosts and even a small attic for a bat nursery.

The Forest Service bought $500 worth of red cedar planks for the houses, and a friend of the Forbes family provided tools and machinery at a local factory for Forbes and 15 friends who built the 20 houses in one eight-hour day. The seams were filled with silicone sealant, a heat-saving design to provide the toasty temperature, up to 115 degrees, that bats often like.

As a wildlife biologist, Keen’s job is to protect animal habitats. But why bats?

“I’m sort of a defender of the underdog, and bats have gotten such a bad rap over the years,” Keen said. “I think they are interesting and fascinating creatures.”

Keen’s fascination with bats first began when she studied the furry creatures as part of her biology degree. “Unfortunately, they were all stuffed,” she said.

She did not encounter the real thing until she joined the Forest Service 18 months ago. She soon learned of bat virtues. The big browns, for example, eat half their weight in beetles, moths and other agricultural pests each day.

Much of bat lore is merely myth, she said. Despite common fears, bats are no more rabid than other wild animals, she said. In the past 26 years, only 10 deaths can be attributed to bat-transmitted rabies in the United States and Canada. More people have died from dog attacks, bee stings or lawn mower accidents.

Keen tried to find a volunteer to build the houses for a year without success. One scout agreed but later backed out. Then in January she heard from Forbes, who was looking for a project he could complete before his 18th birthday in May, the deadline for finishing his Eagle Scout project.

When Keen proposed the unusual venture, Forbes agreed right off the bat. “It’s different,” said Forbes, who also must write a report on the project.

Not all of his friends share his enthusiasm. “Scouts think, ‘Oh, that’s a cool Eagle project,’ ” Forbes said. “But friends of mine ask, ‘Why are you doing that? It’s stupid.’ ”

Forbes confessed that he was not always a bat fan.

“A long time ago, I was real scared of bats,” he said, recalling how bats swarmed around him once during a camping trip in the Redwood National Forest when he was 9. “They were just everywhere. They’d fly straight at you and fly away with a high, piercing chirp. It was just a scary feeling for someone who is 9 years old.”

Now, he is more accepting. But he remains cautious.

“I’m not afraid of them,” he said. “But I wouldn’t like to get too close to a bat.”