Sometimes finding a nest was as easy as stepping behind a pinon pine: Suddenly a bird winged in, nesting material in its beak, and there you had it. Sometimes it meant tirelessly tracking a bird for two days, finally settling under a juniper at the center of its territory to wait it out -- and having your chief rival on the field crew point out that, hey, dude, the nest was right above your head all along.
The competition could be fierce. A nest might be worth five bucks, or maybe an ice cream cone, after the heat came on and the crew piled out of ecologist Clint Francis' dusty pickup truck back at headquarters in Durango, Colo. Mostly, though, it was good for bragging rights.
But for the lanky, brown-haired Francis, who began his study in 2005 and published the results in 2009, the payoff has always been the data. In a world growing steadily noisier, his groundbreaking research, done in the Bureau of Land Management's Rattlesnake Canyon Wildlife Area in northern New Mexico, offers the clearest proof yet of the impact industrial grade noise has on natural communities of birds.
A vast and ancient landscape of arroyos and oak flats, the mesas surrounding Rattlesnake Canyon are pockmarked with 1,500 natural gas well pads and crisscrossed with red clay roads. At least half those well pads are outfitted with humungous compressors continually pushing gas through feeder lines -- and radiating noise in every direction. Ecologists have worried for decades about how sweeping landscape-level changes affect the odds for wildlife. Yet noise can fragment habitat as surely as the physical fact of clear-cuts or interstate highways. And noise, Francis notes, is constantly growing in loudness and ubiquity.
During the past 40 years, the nation's population has grown by a third while road traffic nearly tripled. Eighty-three percent of the continental U.S. is now less than two-thirds of a mile from a road. Since the early 1980s, air traffic has grown by a factor of three; it's hard to find places free of high-altitude noise. But only in the past 15 or 20 years -- about the time those gas wells began going in -- have researchers considered what noise fragmentation looks like on the ground. And what better study subject than birds?
Among animals, birds stand out for their profound reliance on songs and calls. Songs define nesting territories, while calls keep birds apprised of friend and foe -- messages critical for survival and reproduction.
Although other studies have shown a link between, say, traffic noise and declining bird densities, none were able to control for a slew of unrelated variables. Most have looked at bird communities near highways -- "but the impact of traffic
noise is complex," says behavioral biologist Hans Slabbekoorn at Leiden University in The Netherlands. "There are so many confounding factors, such as chemical pollution, being unable to hear birds over traffic noise, and the visual disturbance of moving traffic."
The beauty of Francis' study sites is the scope they lent for a truly natural experiment, meaning he didn't have to add or subtract anything for his experiment to work. All he had to do was watch. His "controls" (sites with quiet soundscapes) and "variables" (sites with noisy soundscapes) were already in place. Each site shared the same basic plants, topography, weather and predators. Each site is populated only by birds native to the West.
The difference? Quiet sites had the acoustic landscape the birds evolved with: the sigh and rustle of wind, the chatter and chirping of chipmunks and cicadas, the yip-yip of coyotes or foxes. The noisy sites were blanketed day and night with an unrelenting din.
Francis' work had its origins in a Bureau of Land Management survey done in 2000 to see whether noisy compressors meant fewer bird species (and individual birds) in nearby forests during the breeding season. The short answer was no. It even suggested that some species were more common in noisy sites. Though the BLM survey team wasn't looking for nests, they couldn't help but notice house finch nests on well-pad equipment next to compressors. These adaptable natives are endemic in the West and expanding their range. And when the survey team turned the compressors off, they saw no indication that birds changed their behavior.
Still, BLM wildlife biologist John Hansen wondered if there might be more to it. He knew that their mere presence doesn't mean birds are establishing nesting territories or caring for young. Was it possible that noise had an impact on reproduction and survival? Hansen called Catherine Ortega, then a biology professor at Fort Lewis College in nearby Durango. Ortega in turn called Francis, at the time doing fieldwork on Mexican spotted owls and willow flycatchers.
Francis and Ortega set up a project to address Hansen's question, following the same basic game plan as the BLM survey. Field crews visited 400- by 60-meter transects laid out at each site. (Each transect is a narrow, randomly chosen study area; it helps keep the data honest.) They rotated among sites -- if a field crew visited one site for the dawn chorus, the next time they'd get to it later in the day. A gas-company rep met crews at each well pad, turning off the compressors for two hours so they could cue into the birds.