North America has recently experienced explosive growth in natural gas extraction, which has raised concerns about associated environmental impacts. One impact that has received less attention is the influence of chronic noise from gas compressor stations that produce loud, continuous, low frequency noise. These stations are scattered throughout landscapes that are important habitat for birds, which rely on acoustic communication to establish territories and attract mates when breeding. This noise could mask acoustic signals, which has been implicated in habitat avoidance, lower breeding success, and altered vocalizations. Our study examined whether forest birds change song characteristics when exposed to noise from compressor stations. We hypothesized that if birds modify their songs to escape noise, then those near compressors will sing faster and at higher frequencies. We identified ten patches of forest near noisy compressors and nine patches near quiet well pads in the Fayetteville Shale of Arkansas. At each site, we recorded singing males of six target species between May-June 2015. We extracted data on song characteristics from spectrograms displayed in Raven Pro, and compared variable means between noisy and quiet sites using independent sample t-tests.
Tufted Titmice (Baeolophus bicolor) changed the number of elements in their songs, with more notes and syllables per song at noisy sites. Tufted Titmice and Northern Cardinals (Cardinalis cardinalis) altered timing by singing faster, delivering more notes per second at noisy sites. Indigo Buntings (Passerina cyanea) and Carolina Wrens (Thyrothorus ludovicanus) had higher minimum song frequencies at noisy sites. The Black-and White Warbler (Mniotilta varia) and Red-eyed Vireo (Vireo olivaceus) showed no response to noise. The differences in species that changed timing compared to those that changed frequency components could be due to the complexity of their songs. Indigo Buntings and Carolina Wrens sing more complex songs, so it may be easier for them to change frequency rather than manipulate the number of notes. Noise also attenuates as it moves through the forest, so birds high in the interior forest canopy (including Black-and-white Warblers and Red-eyed Vireos) are exposed to less noise, and therefore might experience less pressure to change songs. Future research should assess how females and neighboring males respond to altered male songs. These findings contribute to a more complete picture of how the rapid rise in gas development impacts wildlife, and could inform noise regulation guidelines for compressor stations.