Birds sing louder to be heard above human din

We make a lot of noise.

Recent continued discussion of expanded airport noise is one proof of that.

Flight patterns affect more than backyard barbecues, though; birds lose their most important communication tool.

It goes beyond airplanes, of course. Birds suffer because of many noises we make.

We are loud and out of tune with nature: planes, trains and automobiles, leaf blowers, lawn mowers and chain saws.

"Humans have drastically changed much of the world's acoustic background with sounds [we produce] that are markedly different in pitch and amplitude than sounds in most natural habitats."

I found that quote in an ornithological journal article that explained one of dozens of studies on adaptations — or not — by birds to human sounds.

Birds sing to establish nesting territory or to attract mates. They use soft chipping sounds to stay in touch with one another. Baby birds cheep when hungry. Predator alerts are vocal.

Bird lives are built on sound. How do they cope with noisy us?

Black-capped chickadees sing at higher frequencies when noise levels are high.

Robins, already singers before dawn, sing more often at night in areas with significant daytime noise. Other species, singing near airports, begin earlier in the morning, when air traffic is lighter. One study showed flycatchers singing longer songs in noisy areas.

Finches in another study simply stopped singing when airport noise drowned them out. Around here, that pause might extend as far from the runways as St. Louis Park.

White-crowned sparrows in San Francisco responded well to recordings of songs modified to be heard above traffic. The response was stronger than that for their usual songs. Like immigrants adapting to a new country, the birds were using a new language.

At a roadless Idaho stopover site for migrating birds, a recording of urban traffic noise was played, four days on, four days off.

Bird abundance in the test area declined by 25 percent when noise was present. Some species showed "almost complete avoidance" of the areas with traffic sound, according to the research paper.

Modifications to bird sounds or signals are made at a cost. Singing higher, lower, longer, louder burns energy needed for other life functions. And sometimes bird messages simply go unheard.

Nonnative species like house sparrows and European starlings do just fine, by the way. So do pigeons, even those that choose to nest under freeway bridges.

Of all the problems birds face, urban noise seems intractable at best. This is not an endorsement of an 18th-century lifestyle. The world is what we've made it. Unmaking is unlikely. Birds will cope or they won't.