Constant noise—such as from the construction project next door or the car alarm that will not stop—can irritate anyone. And birds are no exception. A recent study found that sounds from oil- and gas-drilling operations contributed to chronic stress in three species of songbirds, mimicking what occurs in people with post-traumatic stress disorder (PTSD).
Nathan Kleist, then a doctoral student at the University of Colorado Boulder, and his colleagues placed artificial nest boxes at various distances from gas-drilling pads in the San Juan Basin of New Mexico. Loud compressors there ran 24 hours a day.
Of the three species Kleist and his colleagues studied, mountain bluebirds and ash-throated flycatchers avoided nest boxes closest to compressors. Western bluebirds, in contrast, nested at sites along the full noise gradient. The researchers measured levels of the stress hormone corticosterone in adult females and nestlings of the three species at all the nest boxes over three years.
The team found a linear relation between distance from the compressors and baseline corticosterone; birds nesting closest had lower stress hormone levels. This may seem counterintuitive, but hormone levels can increase or decrease depending on the type and timing of stress. A sustained change in either direction indicates chronic stress, and research on humans suffering from PTSD shows that their baseline levels typically decline.
The scientists also found that eggs in western bluebird nests closest to the compressors were less likely to hatch than eggs farther away. Nestling growth was stunted closer to compressors in all three species, the team reported in January in the Proceedings of the National Academy of Sciences USA. “With even modest increases in background noise, we could see these effects,” Kleist says. Nestlings farthest away experienced stunted growth as well (predators are more common at quieter sites, and heightened vigilance might reduce the birds' ability to feed their young). Nestlings at intermediate distances had the highest growth rates.
Michael Romero of Tufts University, who studies stress responses in wildlife and was not involved in the study, says, “The neat thing about this paper is that it showed environmental stress lowered [reproductive success].” Even wildlife in highly protected areas is not immune. “Most protected areas in the United States are experiencing increased background noise,” Kleist notes, making this “potentially a widespread issue.”