Deserts are commonly thought of as remote and quiet places. Travel to New Mexico's San Juan Basin, for instance, and you might expect to hear little more than a hot wind whispering through the juniper and piñon pine.

However, a boom in oil and gas activity has transformed the soundscape of this region. Now, depending on how close you are to a well pad or a compressor engine, the desert can resemble the din of a busy office. Or worse. (Get involved with National Geographic's Year of the Bird.)

“Some of the loudest sites can be associated with standing on the tarmac at an airport,” says Clinton Francis, an ecologist at California Polytechnic State University. (Listen to what a compressor station sounds like.)

Francis and his colleagues have been studying what effect such noises has on desert wildlife for years, and they say the newest results—published January 8 in the journal PNAS—are worrisome.

View Images A western bluebird nests in an experimental box provided by the scientists. Photograph by Nathan Kleist

In short, western bluebirds that nest in proximity to oil and gas noises hatch fewer chicks than bluebirds that nest in quiet. This is particularly concerning, because western bluebirds are considered hardy species not particularly sensitive to noise, says Francis, who received funding from the National Geographic Society.

Not only that, but chicks growing up among the industrial cacophony are smaller than those born in more quiet areas, he says.

"A Really Thick Fog"

The scientists were able to come by their findings by placing a network of 240 nest boxes throughout the desert, each at varying distances to oil and gas wells.

The boxes provided the scientists with a way to routinely monitor the birds to check for nest condition and the presence of eggs and chicks. Trap doors on the boxes gave the team a minimally invasive method with which to capture the birds and take measurements, and small blood draws provided insight into how the birds were responding to their environment.

While other studies have looked at how noise can affect stress hormones or fitness in a host of animals, Francis says theirs is the first to combine all of these factors to really pinpoint how noise impacts reproduction.

How or why it does so is less clear, however.

View Images Some of the nestboxes were placed close to the oil and gas operations, as pictured above. Photograph by Nathan Kleist

A study Francis published last year found that desert areas with the most human-caused noise had fewer crickets, froghoppers, grasshoppers, and velvet ants—suggesting birds that nest in such areas may simply have less food. It's possible the birds simply don't realize that the sounds are bad for them—a concept called an "ecological trap."

Noise could also be interfering with communication between adult bluebirds, or drowning out the birdsong that alerts other animals in the community about predators.

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It might be difficult for us to comprehend just how much of a burden noise can be to animals, notes Francis, because humans are primarily visual creatures. But thinking of hearing like vision might help. (Read: "High Levels of Dangerous Chemicals Found in Air Near Oil and Gas Sites.")

“It’s like navigating through a really thick fog,” he says. “Imagine you’re trying to traverse across some landscape and all you can see is 10 or 15 meters in front of you, where under normal conditions your sightline could be miles.”

Stress Signals

Francis and colleagues also found that stress hormone levels go down in western bluebirds, mountain bluebirds, and ash-throated flycatchers that experience chronic noise.

View Images The study included analysis of the ash-throated flycatcher. Photograph by David L. Keeling

This is surprising, because it's thought that higher levels of these hormones, also known as glucocorticoids, are the best indicator of stress. In this case, it seems that the birds’ bodies have had to tamp down that response in order to survive. (Read how U.S. air pollution once turned birds black.)

"That’s a really interesting finding and it’s kind of one of the newer ideas to come out of the last decade about how stress hormones work,” says Sue Anne Zollinger, a behavioral physiologist at Max Planck Institute for Ornithology in Germany.

View Images The mountain bluebird also showed lower levels of stress hormones in response to chronic noise. Photograph by David L. Keeling

Overall, Zollinger says, there's a lot of variability among species and how they respond to human sounds. For instance, adult zebra finches she exposes to noise pollution in her lab don’t seem to mind, but juveniles are heavily affected. For instance, these affected chicks were smaller and aged faster than those not exposed to noise.

What’s more, Chris McClure, an ornithologist and director of global conservation science for the Peregrine Fund, says the study refutes the notion that birds will get used to noise.