We humans are noisy, and birds don't like it. Some birds change their tunes to deal with the din.
Now it seems that other birds are just packing up and moving away. A new study in today's issue of PLoS ONE finds that this strategy is particularly true of larger songbirds such as western tanagers (above), whose low-frequency calls are simply drowned out by human-made ruckus.
The findings aren't just important for birds. Some of these larger noise-intolerant species, such as scrub jays (below), are also important seed dispersers for trees like pines and oaks. That could mean bad news for tree seedlings, too.
To be clear, the birds are not moving away because hikers are talking too loudly. The study site, Rattlesnake Canyon Wildlife Area in northern New Mexico, is home to thousands of natural gas wells, many of which are coupled with noisy compressors that run day and night at 80 decibels — as loud as a motorcycle less than 50 feet away. From 2005 to 2007, biologists counted birds and nests in areas at various distances from the noisemakers.
The advantage of this New Mexico site was that the researchers could tease apart the effects of noise from other confounding factors often associated with noisy areas like roadways or cities, such as pollution from light or chemicals or collisions with cars, explained the study's lead author, Clinton Francis of the National Evolutionary Synthesis Center in Durham, N.C., in a press release.
Francis and his colleagues say the bigger birds were essentially forced out of the noisy sites because they simply couldn't hear each other. Most machinery noise is lower in frequency and more constant than sounds found in nature. Tanagers and jays may be louder than sparrows and finches, but their songs are at the lower frequencies more easily drowned out by the compressor noise.
The next step is to determine whether bird species living in other types of noisy environments show the same pattern. "This may not be restricted to oil and gas lands in New Mexico," Francis says. "We'd like to know if we see the same trend in response to city and traffic noise, and man-made noise more generally."
Western tanager. (Wikimedia Commons)
Noisy gas well site in northern New Mexico. (Courtesy Clinton Francis)
Western scrub jay. (Wikimedia Commons)