Few topics have netted the attention of environmental professionals in South Carolina the way these winged mammals have over the last 20 months. Since September 2022, South Carolina has witnessed changes in protection status for two species, the first record of a third protected species, and now hearing news that protection for a fourth species may be on the way. No matter your place in the environmental field, it is likely that bats have come to roost in one of your project sites. Environmental regulators, planners, engineers, and scientists play a pivotal role in the decision-making that affects these imperiled mammals. It is crucial for all of us to understand the bats in our state, the latest updates and guidance for evaluating bats on your project, and the anticipated changes still to come.

South Carolina is home to 15 species of bats, each being integral contributors to the State’s ecosystem and economy. Bats keep insect populations in check, including pests of the forestry and agriculture industries. According to the South Carolina Department of Natural Resources (SCDNR), bats’ consumption of pests offsets approximately $115 million of pesticides in South Carolina annually, saving $22.9 billion across the United States.¹ Not only is this a huge cost-savings, but that reduction in pesticide use lessens the amount of toxic chemicals in our environment that may impact other wildlife. As bat populations decline, these ecosystem services and the biodiversity of our state are at risk. Anthropogenic factors like wind turbines, modification of caves and mines, and habitat loss due to development are having a negative impact on bat populations throughout the country.

Perhaps the greatest threat to bats is white-nose syndrome (WNS)—a fungal disease that disturbs bats during hibernation and is known to eliminate entire colonies. According to SCDNR, the tricolored bat (Perimyotis subflavus), once widespread across the eastern United States, is currently proposed to be listed as ‘Endangered’ under the Endangered Species Act (ESA) due to WNS.  In November 2022, the northern long-eared bat (Myotis septentrionalis) received an elevated status from ‘Threatened’ to ‘Endangered’, also due to WNS. South Carolina has become a land of hope and relief for both the tricolored bat and the northern long-eared bat, with only 10 of the 46 counties known to contain the WNS fungus.² Although the northern long-eared bat has a limited range in the state, the species has begun to adapt to coastal living. In 2016, northern long-eared bats were captured during surveys in Beaufort County—the first record of the species outside of the upper foothill regions of Oconee, Pickens, and Greenville counties.³ Since then, more records of northern long-eared bats have been reported throughout the coastal zones of North and South Carolina that are successfully living and reproducing far away from the fungus-harboring karst environments of the species’ traditional range. Similarly, although much more widespread, the tricolored bat seems to be doing well in South Carolina compared to other parts of its range. Tricolored bats are known to occur in every county in South Carolina and are commonly detected during acoustic and mist-netting surveys (these surveys will be discussed later). Perhaps due to this great news of success in the Palmetto State, a rare newcomer has made itself at home. The gray bat (Myotis grisescens), which has been protected under the ESA since 1976, was not known to occur in South Carolina until fall 2023 when individuals were discovered during structural surveys in Greenville and Oconee counties.⁴

The presence of these federally protected species within our state means that any project with federal funding or requiring a federal permit must evaluate potential impacts to the bats. In general, construction activities that will impact trees, bridges, or culverts can threaten individuals of these species who already have an uphill battle for survival. To facilitate project planning and avoiding bat impacts, the United States Fish and Wildlife Service (USFWS) has mapped bat activity levels into zones that reflect the typical lifecycle of bats in a given area. In South Carolina, there are two zones of bat activity: the Hibernating Range and the Year-round Active Range. The upper elevations of Oconee, Pickens, and Greenville Counties lie within the Hibernating Range while the rest of the state is within the Year-round Active Range for tricolored and northern long-eared bats. Bats are most vulnerable to construction activities during their hibernating period and pup season, when the bats are unable to safely fly away from potential danger. In the Hibernating Range of South Carolina, USFWS has designated November 16 through March 31 as the hibernation timeframe and May 15 through July 31 as the pup season. In the Year-round Active Range, December 15 through February 15 is considered the Winter Torpor timeframe, a “shallower” hibernation where periods of inactivity are not as long, and the bats are not in quite as deep of a winter slumber. May 1 through July 15 is considered the pup season in the Year-round Active Range, arriving sooner in the year but lasting just as long as the Hibernating Range pup season. These timeframes come with restrictions to certain disruptive activities, primarily tree clearing for projects within the northern long-eared bat range and are anticipated for the tricolored bat range once it is officially listed.⁵

Of course, these restrictions can potentially pose a threat to project schedules and consultation with USFWS may be necessary to address those concerns. If a project is not able to commit to avoiding those timeframes, there is the option to conduct presence/absence surveys to determine if any protected species occur within the project area. These surveys include passive and active survey techniques. Passive surveys, like acoustic surveys, involve placing detectors on site that record high-frequency calls made by bats that fly through the project area. These calls can be deciphered to determine which species are present using USFWS-approved software. Active surveys, like mist-netting, involve capturing bats and collecting data from each individual that flies through the project area into a deployed net. Active surveys are helpful to assess the presence of bats that do not have acoustically distinct calls from other species, like the Indiana bat (Myotis sodalis) and little brown bat (Myotis lucifugus), and they can produce more concrete evidence of the bats living nearby. However, active surveys require the biologist conducting the survey to have a federal collection permit, often making it a more expensive strategy than passive surveys. Passive acoustic surveys are the more common method in South Carolina, providing a sampling of bat activity within the project area in a timely and cost-effective manner. In the Hibernating Range, these surveys can be conducted between May 15 and August 15. In the Year-round Active Range, surveys can be conducted between March 1 and October 15. Pending the results of the surveys and the details of the project, USFWS can provide options for facilitating the project while avoiding and minimizing negative impacts to bats.

While we await the official listing status of the tricolored bat (and hopefully some programmatic agreements), another declining bat species has the attention of USFWS. The little brown bat, another victim of WNS, is currently under review to be considered for listing and protection. Like tricolored bats, the little brown bat is present in every county in South Carolina.⁶ It is not currently known if or when the little brown bat may receive protection status, but their decline is a somber reminder that bats are increasingly imperiled as time goes on. As environmental stewards, it’s imperative to prepare for these changes and continue supporting the recovery of these essential nocturnal animals. Their protection is not just about preserving biodiversity, but also about maintaining the ecological balance and the health of our natural environments.

Wade Biltoft, PWS

Environmental Project Manager

Three Oaks Engineering

Wade Biltoft, PWS | LinkedIn

1) SCDNR. Bats in South Carolina. https://www.dnr.sc.gov/wildlife/bats/index.html

2) SCDNR. Bats and White-nose Syndrome (WNS). https://www.dnr.sc.gov/wildlife/bats/batswns.html

3) SCDNR. Bats in South Carolina – Northern Long-eared Bat. https://www.dnr.sc.gov/wildlife/bats/NLEB.html

4) SCDNR News. https://www.dnr.sc.gov/news/2023/Nov/nov15-bats.php. November 15, 2023.

5) USFWS. “Range-Wide Indiana Bat and Northern Long-Eared Bat Survey Guidelines.” March 2024.

6) USFWS. https://www.fws.gov/species/little-brown-bat-myotis-lucifugus