Scientists want to know why birds warble long after dark

FRESNO -- Why do the birds go on singing -- at night? The common expectation (right up there with the sun rising in the east, leaves dropping in the fall and the cat wanting back in as soon as someone has let it out) is that birds sing in the sunshine.

They're supposed to be early birds, right? But across Fresno, more-than-casual observers have noticed birds singing long after dark this summer.

"Isn't it weird that the birds are singing at night?" Susan Daughty's teen daughter asked when her mother came home from a dinner shift waiting tables.

"I listened and then I thought, 'Well, that is strange,' " said Daughty, who lives in central Fresno. "It was after 9 p.m. and they were singing away. But I didn't know if it was new or if I just hadn't listened before." Therein lies the mystery.

Were the birds singing at night all along and people just now noticed? Could mockingbirds -- those raucous late-night partiers of the bird world -- be mocking the sound of songbirds? Could a cat with hunting prowess have moved into the neighborhood, keeping the birds awake at night? Or is it another sign of city life changing the natural world?

In England, researchers found that the British robin was forced to sing at night because daytime traffic was drowning out his mating serenades.

The study by Richard A. Fuller and colleagues at the University of Sheffield, published in 2007, measured noise levels and singing at 67 sites around their city. They found that birds sang only during the day at 49 sites, and day and night at 18 sites. Daytime noise levels at those 18 sites were significantly higher than at the others.

Madhusudan Katti, an assistant professor of vertebrate ecology in the biology department at California State University, Fresno, thinks it's "very possible" that birds in Fresno are being forced to sing at night because of higher noise levels in the daytime.

Katti is overseeing one study on the effect of ambient noise on the singing behavior of house finches -- pretty, red-chested birds common in the area.

Heather Hanlin, a first-year graduate student at the university, collected audio of the house finch at more than 30 locations across Fresno County. Hanlin did her recordings in the daytime, some by highway overpasses, some on quiet streets.

"We're just now beginning to compile the data," said Katti, whose research focuses on biodiversity in urban settings. "There's not enough information to know why birds sing when they do, how noise affects bird song; that's why we're doing the study."

Study may be expanded

Somewhere along the way, Hanlin noticed that the birds were singing after dark. "I heard them. But this summer was my first time recording. So I didn't know if the birds had just started singing at night or if I was just so tuned into bird song that I was hearing it for the first time."

For Katti and Hanlin, the questions immediately begin to arise when they ponder birds singing at night.

What kind of birds? What kind of songs? Which neighborhoods?

"I'd be very interested to talk to people who've heard birds singing at night," said Katti, who may expand his study. "We could learn something."

A journalistic, unscientific survey around the city found people who said they heard after-hours warbling.

Makielah Vandervelde, 8, who lives in north Fresno, says she lies awake at night listening to the birds.

"I was really surprised, because usually birds go to sleep at night," she said.

Anidelle Flint, 79, who lives in Fig Garden, says the birds have been chirping and singing at night in her neighborhood this summer.

"No, the birds haven't been singing after dark," said her husband, George Flint, 78. "Oh wait, maybe they do. I take my hearing aid out at night. But if they do sing at night, I would like that. I like birds singing anytime."

Michael Ruffino, owner of the Wild Bird Center, a bird supply store, says he has heard birds singing at night.

But he says he's doubtful there are any far-reaching theories on the reasons why.

"I like the obvious answers," he said. "If the birds are singing in your neighborhood at night and they weren't singing last summer, it's probably because a tomcat that's a really good birder moved into the neighborhood.

"Throw a cat up a tree and the birds will make some noise," he said. "Throw a cat up a tree and those birds will sing all night."

This story was originally published August 19, 2008 at 4:44 AM with the headline "Scientists want to know why birds warble long after dark."