Written by Torin Miller, Research Assistant
A few weeks ago, we took a look at the impacts of shale gas drilling on wildlife populations, with a particular focus on habitat fragmentation, water issues, and noise, light and air pollution. This week, we’ll take a closer look at species-specific impacts throughout the northeastern United States, with an emphasis on the Marcellus Shale region. Specifically, this article will focus on forest songbirds and bats, and the impacts that habitat fragmentation, greenhouse gas emissions, water consumption and contamination, and noise pollution have on their populations.
Forest songbirds and various bat species have been at the center of the majority of the wildlife-related shale gas impact studies conducted to date. The Marcellus shale region is covered by large swathes of contiguous forest, which provides “habitat for a myriad of forest specialists and interior wildlife, including numerous species of conservation concern and many Neotropical songbirds,” a study in The Journal of Wildlife Management (JWM) states. According to the study, with less than 10 percent of the nation’s forests remaining in contiguous conditions, Pennsylvania’s title as the second most-forested state in the northeast is incredibly important for forest specialists such as songbirds and bats. “Bats may serve as the proverbial ‘canary in the coalmine’ because many of their life history traits make them sensitive to human-induced environmental changes,” a report by The Delaware Riverkeeper Network (DRN) notes.
Specific, potential impacts on both forest songbirds and bats, with a focus on habitat fragmentation, greenhouse gas emissions, water consumption and contamination, and noise pollution, will be outlined below.
Shale gas development’s biggest impact on forest songbird populations is habitat fragmentation. This is likely attributed to the fact that songbird breeding success and abundance are highest in large blocks of contiguous forest, according to a study in Environmental Science and Technology (EST). According to the JWM study, “Research has shown that shifts in the bird community are occurring within the large block of extensive forest in Northcentral Pennsylvania in association with shale gas development.”
The JWM study found that there has been an increase of human tolerant species near well pads and a decline in forest specialists, and that the lack of forest specialists may have been the result of edge avoidance or an influx of new species. As a result, “[t]he increase in these novel community members within the forest may result in increased levels of predation, parasitism, and resource competition,” the study notes. The loss of forest specialists is important for a variety of reasons. Notably, forest songbirds are important for insect control; “[t]hey provide a valuable ecosystem service and their role in preventing and suppressing insect outbreaks is well-documented,” the study states.
While habitat fragmentation related to shale gas development casts the biggest shadow over forest songbirds, resulting noise pollution also has its impacts. The EST study notes that noise associated with shale gas development (both short-term drilling and long-term compressors) may harm vocal species like songbirds. Additionally, a study in The Wildlife Professional notes that loud noises may affect the pairing success of songbirds, as their mating songs are drowned out by external noises. The study also notes that unnatural noises may create the possibility of “lower abundance, changes in reproductive behavior and success, altered predator-prey interactions and altered avian communities.”
According to the JWM study, “it is important to minimize disturbance to core forest habitat by minimizing fragmentation and the number of new pads established.” The study notes that methods to minimize disturbance include “clustering pad locations, maximizing the number of wells per pad, and identifying and excluding from shale gas development areas of high quality contiguous forest.”
Like forest songbirds, various bat species are impacted by shale gas development. These impacts primarily originate from habitat fragmentation, water consumption and contamination, and greenhouse gas emissions.
Bat abundance and diversity is highest when natural habitat is highest, and mature forests provide many places for bats to roost, according to the DRN report. Particularly, bats need large areas of undisturbed, mature habitat for roosting and foraging, and shale gas development may disrupt large areas (and will likely continue to do so), the study added.
Destruction or disruption of hibernacula is also a concern, particularly for the endangered Indiana bat (Myotis sodalis), which are known to hibernate at only 18 sites throughout Pennsylvania, according to the Pennsylvania Game Commission. Bats require hibernacula with specific microclimate conditions, including temperature, humidity and airflow. “Modifications to the surface habitat surrounding hibernacula also can contribute to changes in microclimate conditions, as well as influence the suitability of foraging characteristics,” the DRN report notes. The report also notes that disturbing hibernating bats can cause bats to lose necessary fat reserves and abandon roost.
Bats rely on water for two primary purposes: personal consumption and prey attraction. First, “[b]ats have relatively high rates of evaporative water loss, and must obtain much of their intake from available surface water resources,” the DRN report states. Additionally, lactating females will select roost sites near water sources to aid in milk production, the report notes. Second, riparian habitats attract insects, which bats prey upon heavily. “Thus, the extensive withdrawal of water resources from the environment, particularly in sensitive areas or areas under drought conditions, will presumably affect roost-site selection and abundance and availability of prey,” according to the report.
Wastewater contamination from shale gas development is a concern for bat populations throughout the northeast. According to the DRN report, “[b]ats have been observed congregating and drinking from holding ponds at industrial sites,” and contaminants in ponds or other water sources can negatively impact insect populations. Insects that ingest contaminated water and are then preyed upon by bats may be harmful; “[b]ecause dietary accumulation and metabolic capacity increase at higher trophic levels, and because insectivorous bats are apex predators, bats are likely more susceptible to contaminants,” the report states.
Lastly, greenhouse gas emissions resulting from shale gas development may impact bat populations. Bats may be highly affected by climate change because temperature changes affect hibernation, food availability and young recruitment, according to the DRN report. Warmer winter temperatures could affect energy requirements for hibernation, and spring births may occur too early, which would increase juvenile mortality and negatively impact recruitment, the report notes.
Overall, “[a]s with other industrial practices, shale gas development contributes to water withdrawal and contamination, habitat loss and degradation, and the emission of GHGs resulting in detrimental effects on bat populations and their environment,” the DRN report concludes.
While more observation and analysis is necessary to truly understand the impacts of shale gas drilling on forest songbird and bat populations, current studies do provide insight into the potential impacts of habitat fragmentation, greenhouse gas emissions, water consumption and contamination, and noise pollution have on these populations, particularly throughout the northeastern United States. A subsequent Spotlight article will take an in-depth look at legal implications of wildlife-related impacts of shale gas drilling, with a focus on policy and legislation that relates to, and resulted from, these impacts.