Little Brown Bat: A Common Bat with Uncommon Problems

Posted to POWER Engineers—Environmental in the Utility Management Group
image credit: Small but mighty. The little brown bat body is approximately the size of a human thumb with a wingspan of roughly 10 inches. During certain times of the year, it can eat more than its body weight in insects each evening.
Bill Doering's picture
Senior Biologist, POWER Engineers

Bill Doering is a senior wildlife biologist and researcher with 10 years of experience in the power sector and over 20 years of total career experience providing regulatory compliance support and...

  • Member since 2022
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  • Dec 20, 2022

The little brown bat (Myotis lucifugus; LBB) was once the most common bat in North America. For many Americans, it’s the bat most likely observed during warm summer evenings darting from concealment in a chimney or barn, dipping over a pond to drink or diving in pursuit of mosquitoes or other insect prey.

In recent years, however, LBB populations have experienced unprecedented declines. The highly contagious novel fungal disease, white-nose syndrome (WNS), has spread across much of the species’ range, posing a major threat to its survival. These declines prompted the U.S. Fish and Wildlife Service (USFWS) to conduct a Species Status Assessment to determine if the LBB should be listed under the Endangered Species Act (ESA).

Although the LBB is found throughout the U.S., an ESA listing of LBB would most impact infrastructure project planning and compliance in the western U.S. where no federally protected bat species currently exists.

To prepare, project proponents should understand what changes are coming to successfully navigate the regulatory requirements associated with an ESA-listed bat species.

White-Nose Syndrome and Why It Matters

Historically, the predominant threats to many bat species have been habitat loss and the intentional killing of bats in their roosts. In most areas, the LBB has been resilient and able to maintain a healthy population in proximity to humans. With few exceptions, it has remained common or abundant in the majority of its historic range without the need for strict regulatory protections.

White-Nose SyndromeIn the past two decades, however, the resiliency has changed. Emerging threats have become the leading stressors of bat populations. For LBBs, the most significant stressor is WNS, a newly categorized described fungus that first appeared in a New York hibernation cave in 2006 before spreading throughout the continent.

WNS causes immense metabolic and water stress in hibernating bats, with death occurring 70 to 90 days after infection. In the northeastern U.S.—the core of the species range—more than 90% of LBBs have been wiped out by WNS. The disease has affected 12 North American bat species to date, but three species, including LBBs, are particularly vulnerable.

Because bats typically feed on insects during summer months, the loss of bats from WNS has significantly impacted ecosystems and affected agriculture by increasing the need for pesticides.

Although WNS has devastated bat populations in the eastern U.S. for 16 years, it has only impacted the western U.S. for the past six. Recent data from a large cave in Montana, however, indicates that the eventual pattern of decline for LBBs in the west will mirror the east.

Project Impacts in the West

In the eastern U.S., there will be few practical changes in resource management, project planning, agency coordination and mitigation, since similar bat species have had federal protection for decades. As a result, agencies, project proponents and other stakeholders in this region are experienced in navigating the requirements associated with ESA-listed bat species.

In contrast, a large portion of the western U.S. will have a federally-listed bat species for the first time, introducing agencies and project proponents to a new regulatory environment. How states and federal land managers will react is unknown at this time. Impacts to land management planning, agency requirements, scientific collecting permits, field survey needs for NEPA actions, reporting requirements and avoidance and mitigation measures will vary among agencies and habitat types. In many areas, resource management plans will require amendments and consultations under Section 7 of ESA. State wildlife agencies will be required to play an expanded role in species protection and permitting under Section 6 of the ESA.

Among federal land management agencies, timber management practices in western National Forests will likely be affected the most, as ESA-listed forest bat species do not currently exist there. Much of the non-forested, arid west will be considered “marginal” habitat for active LBBs in summer, and the priority for USFWS will be direct impacts (e.g., killing bats) rather than indirect impacts (e.g., habitat loss).

For infrastructure project development, the regulatory environment will alter. Bat best management practices will be documented in standard lists. Additional surveying and monitoring requirements may be imposed. Seasonal restrictions for certain activities, such as tree clearing, will be required. Avoidance buffers will be identified around important resources or landscape features.

Blasting will be restricted near caves or mines for hibernation site protection. Accessory plans, such as weed or pesticide plans, may require updates. Development of projects without a federal trigger may require bat protection plans or bat-specific Habitat Conservation Plans under Section 10 of ESA.

Because LBBs frequently accompany other protected and sensitive resources, many standard practices and mitigative actions already avoid, minimize or mitigate impact to bats. For example, seasonal or spatial restrictions to protect birds under the Migratory Bird Treaty Act may also benefit bats.

In addition, the National Historic Preservation Act and the Cave Resource Protection Act afford protections that concurrently protect bats in roosts. Avian and Bat Protection Plans are already required in many areas without ESA-listed bat species.

A comprehensive review of project-specific requirements and permits may reveal that established requirements support USFWS direction to avoid “take” under ESA. Significant changes may result from increased analysis, documenting and coordination.

USFWS Response to Declines

To support the Species Status Assessment, the USFWS reached out to state, federal and tribal natural resource agencies across the U.S. to collect data and solicit expert input. The assessment included the three bat species most affected by WNS: northern long-eared bat, tricolored bat and LBB.

Each species has its own assessment trajectory. Because the assessment for the LBB was at the discretion of USFWS and not triggered by a petition or legal action (unlike the other two assessed species), there is no court-ordered, enforceable timeframe for publishing an ESA listing decision. Currently, the status of LBB is under “Discretionary Status Review” by the USFWS.

The presumption among many western resource managers is that an ESA-listing decision for the LBB will be published in the Federal Register in March 2023 and listed as Threatened, due primarily to WNS. Climate change and habitat loss are additional exacerbating factors. A rule delineating species protection under Section 4(d) of ESA will be subsequently published.

Because of general ecological similarities and habitat use, the rule will likely be modeled after a rule published in 2015 for the northern long-eared bat. Reducing WNS spread and protecting important habitat at landscape and site-level scales will be critical drivers in the rule. No critical habitat is likely to be designated.

The LBB and Future Project Compliance

The listing of the LBB will bring important regulatory changes to the western U.S. With proper planning, proactive coordination, good stakeholder relationships and communication, scientifically defensible data, thorough documentation and expert consultation, impacts to projects should be minimal.

Article originally published in the Winter 2022-2023 issue of Currents. Subscribe today to stay current on environmental insights and regulatory updates that impact your projects. 

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Mark Silverstone's picture
Mark Silverstone on Dec 29, 2022

"In contrast, a large portion of the western U.S. will have a federally-listed bat species for the first time, introducing agencies and project proponents to a new regulatory environment."

I guess this will be something of a test to see if the EPA can hold the line on the Endangered Species Act with respect to the three bat species? 

Is your job to help your clients operate in compliance with whatever rules are adopted?

Do you anticipate that the regulations can be effectively drafted, implemented and enforced?

Bill Doering's picture
Bill Doering on Feb 8, 2023

Your EPA question is a good one. Since pesticides are a recognized risk to insectivorous bats in general, it will be interesting to see how USFWS handles this when the proposed rule for listing is published. My presumption is we will see seasonal or spatial buffers recommended (for things like herbicide application) around important habitat areas used by bats, e.g. hibernation caves/mines, maternity roost complexes and important feeding or drinking areas. Many of these areas already receive pollutant or other protection under other regulations or permitting.

My expectation is that responsible agencies are already working with USFWS for a smooth transition to a new listed bat. The sad reality is that the management of common species with stable populations is a bit loose; but when something is listed under the Endangered Species Act suddenly the pencils need to be sharper. I co-chair a regional bat working group and will hear more on this topic at our annual meeting in a few weeks.

And yes, my job has been to keep my clients in compliance with sensitivity to potential impacts to schedule and budget.

Todd Carney's picture
Todd Carney on Dec 30, 2022

Wow this is a very interesting post. Have you encountered any issues with other species?

Bill Doering's picture
Bill Doering on Feb 8, 2023

Prior to the emerging threats discussed in my article, new bat listings under the Endangered Species Act were exceedingly rare. The little brown bat situation is probably most similar to what occurred when northern long-eared bat was first listed as threatened about eight years ago. Agencies and project proponents in areas in the eastern U.S. outside the range of Indiana bat (listed, endangered) but within the range of northern long-eared bat had new bat requirements where that had not previously. There were definitely challenges as agencies adapted during the first year after listing.

Nevelyn Black's picture
Nevelyn Black on Dec 31, 2022

"Because bats typically feed on insects during summer months, the loss of bats from WNS has significantly impacted ecosystems and affected agriculture by increasing the need for pesticides."  It’s a butterfly effect.  The loss of these little guys could lead to much bigger problems in the ecosystem.  Design changes and deterrents may reduce the impact wind turbines are having on birds but determining how to reduce disease, habitat loss and bat deaths should be a priority.  I am interested to find out what the ‘best bat practices’ are.

Bill Doering's picture
Bill Doering on Feb 8, 2023

Specific best practices will certainly vary with project, habitat and type of potential impacts. Some insight might be gained by taking a look at the 2015 northern long-eared bat section 4(d) rule and habitat conservation plans prepared for areas within the range of Indiana bat. Little brown bat has aspects of its natural history that are similar to these two species. The most broadly applied “best practice” may be seasonal restrictions on tree clearing so as to not impact forest maternity roost habitat of little brown bats. These sorts of measures would be new to western land managers and challenging in federally managed forests. To your point regarding the “butterfly effect,” a recently published study of bats in Germany found that human-caused mass mortality of bats resulted in large-scale losses of trophic interactions and impacted both agriculture and silviculture.

Bill Doering's picture
Thank Bill for the Post!
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