No two species delay more US infrastructure projects than the Indiana bat and the northern long-eared bat. If your project is anywhere in the eastern half of the country and involves tree removal, building demolition, or bridge work, you will encounter these species in your Section 7 consultation.
This guide covers the survey requirements, seasonal timing, permit obligations, and the 2024 programmatic consultation framework that can streamline your compliance pathway.
Why These Two Species Matter So Much
The Indiana bat (Myotis sodalis) has been listed as Endangered under the ESA since 1967. The northern long-eared bat (Myotis septentrionalis) was listed as Endangered in 2023, upgraded from its previous Threatened status after devastating population declines from white-nose syndrome.
Together, these two species have ranges that cover most of the eastern United States - from the Great Plains to the Atlantic coast, and from the Gulf states to southern Canada. Any project with a federal nexus in this range must address them during Section 7 consultation.
The practical impact is enormous. Road widening projects, bridge replacements, transmission lines, pipeline corridors, wind energy facilities, and residential developments all routinely trigger bat consultation. Understanding the survey requirements and compliance pathways saves months of project delay.
The Tricolored Bat: The Third Species to Watch
The tricolored bat (Perimyotis subflavus) was proposed for Endangered listing in 2022, with a final rule expected. Environmental consultants should already be addressing tricolored bat in their assessments, as the species will likely be listed by the time many current projects reach construction.
The December 2024 Programmatic Biological Opinion for Transportation Projects now covers all three species, making it essential reading for anyone working on federal-aid highway projects.
When Are Bat Surveys Required?
Bat surveys are typically required when your project involves:
Tree removal of any tree greater than 3 inches DBH (diameter at breast height) during the bat active season (April 1 - October 31). Trees with loose bark, cavities, crevices, or exfoliating bark are potential roost sites.
Bridge or culvert work where structures may support roosting bats. Bridges with expansion joints, crevices between concrete sections, or wooden components are frequently used as roosts.
Building demolition or renovation where buildings have gaps, loose siding, shutters, or attic spaces accessible to bats.
Cave, mine, or tunnel disturbance at any time of year, but especially during hibernation (October - March).
Wind energy projects where turbine placement may cause bat mortality.
Linear infrastructure (roads, pipelines, transmission lines) that requires clearing forested corridors.
Survey Types
Phase 1: Habitat Assessment
The first step is always a habitat assessment. A qualified biologist visits the site to evaluate whether suitable bat habitat exists.
What they look for:
For roosting habitat - trees with exfoliating bark (shagbark hickory, white oak, dead/dying trees), cavities, crevices, or other features that could shelter bats. Buildings with gaps, loose siding, or accessible attic spaces. Bridges and culverts with crevices.
For foraging habitat - proximity to water, forest edges, hedgerows, and other linear features bats use for navigation and foraging.
For hibernacula - caves, mines, tunnels, or other underground features within the project's zone of influence.
Timing: Year-round, though best conducted April - October when vegetation and tree condition are most visible.
Outcome: The habitat assessment determines whether Phase 2 surveys (presence/absence) are needed. If no suitable habitat exists, no further bat surveys are required and the project can proceed with a "no effect" or NLAA determination.
Phase 2: Mist-Net Surveys
Mist-net surveys are the gold standard for confirming bat species presence. Fine mesh nets are deployed across flight corridors (forest edges, streams, trails) at dusk and checked throughout the night.
Timing: June 1 - August 15 (peak activity period). Some USFWS field offices accept surveys from May 15 - August 15.
Effort: Minimum 2 nights of netting per site, with nets deployed from sunset to at least 5 hours after sunset. Net placement follows USFWS guidelines for the specific field office.
Permit: A federal Section 10 scientific permit is required to handle federally listed bats. The permit holder must have documented experience with bat identification and handling.
Species identification: Captured bats are identified to species, measured, sexed, aged, and assessed for reproductive condition. Indiana bats are distinguished from similar Myotis species by their keeled calcar, small foot size, and pinkish lip coloration.
Phase 2: Acoustic Surveys
Acoustic surveys use bat detectors to record echolocation calls, which are then analysed to identify species. Acoustic surveys can supplement or, in some cases, replace mist-net surveys.
Timing: May - September (active season). Best results June - August.
Equipment: Full-spectrum bat detectors (e.g., Wildlife Acoustics SM4BAT, Pettersson D500X) deployed at potential roost sites and along foraging corridors.
Analysis: Recorded calls are analysed using auto-classification software (Kaleidoscope, SonoBat) and manually vetted by an experienced acoustic analyst. Indiana bat and NLEB calls can be difficult to distinguish from other Myotis species acoustically.
Limitations: Acoustic surveys can confirm species presence but generally cannot confirm absence. A negative acoustic result does not definitively mean the species is not present. USFWS acceptance of acoustic-only surveys varies by field office.
Emergence Counts
If a roost is identified (in a building, bridge, or tree), emergence counts determine the number of bats using the roost.
Timing: May - August, conducted at dusk. Multiple counts may be required.
Method: Observers positioned around the structure count bats as they emerge at sunset. Infrared cameras or night vision equipment improve accuracy.
The 2024 Programmatic BiOp for Transportation
The December 2024 Programmatic Biological Opinion for Transportation Projects covering Indiana bat, NLEB, and tricolored bat is a game-changer for highway and bridge projects.
What it covers: Projects funded or authorized by FHWA, FRA, or FTA that may affect these three bat species.
How it helps: Instead of individual formal consultation for each project, the programmatic BiOp establishes:
- Standard conservation measures that projects can adopt
- Effect thresholds that determine whether a project fits within the programmatic framework
- A streamlined verification process instead of full project-by-project consultation
Key conservation measures include:
- No tree removal April 1 - October 31 (or May 1 - September 30 in some regions) without prior habitat assessment
- 150-foot buffer around known roost trees
- Seasonal restrictions on bridge work where bats are present
- Lighting restrictions near known roosts and foraging areas
When you can use it: If your transportation project fits within the programmatic framework's activity types and effect thresholds, you can use the streamlined process. Check with your local USFWS field office and FHWA division office for details.
Seasonal Timing Summary
April 1 - October 31: Bat active season. No tree removal over 3 inches DBH without biologist clearance.
June 1 - August 15: Mist-net survey window. This is the critical window - if you miss it, you wait until next year.
May - September: Acoustic survey window.
October - March: Hibernation period. No disturbance to caves, mines, or known hibernacula.
December - February: Winter hibernacula surveys (requires separate permits and protocols).
Practical Tips for Consultants
Start habitat assessments early. If your project involves tree clearing in the eastern US, commission a bat habitat assessment as soon as the project is scoped. If suitable habitat is found, you need the full active season (June-August) for mist-net surveys.
Know your field office. USFWS field offices have different survey protocols, acceptable survey windows, and levels of flexibility. What works in the Midwest field office may not be accepted in the Northeast. Contact your local field office early.
Use IPaC and EcoCheck together. IPaC generates the official species list for Section 7 consultation. EcoCheck shows you actual bat occurrence records from GBIF - where bats have been documented near your site - which informs your habitat assessment and survey design.
Document everything. Negative results are just as important as positive results. A well-documented habitat assessment that finds no suitable roost habitat is valuable evidence for a "no effect" determination.
Consider the programmatic BiOp. If your project is a transportation project, check whether the 2024 programmatic consultation applies. It can reduce consultation from months to weeks.
Key Legislation
- Endangered Species Act (16 U.S.C. 1531-1544) - Indiana bat listed Endangered 1967, NLEB listed Endangered 2023
- Section 7 consultation required for all federal nexus projects
- Section 10 scientific permit required for mist-netting federally listed bats
- USFWS Range-wide Indiana Bat Survey Guidelines
- 2024 Programmatic BiOp for Transportation Projects (Indiana bat, NLEB, tricolored bat)
Start With the Desktop Data
Before scoping any bat survey, check what's already known about your site. EcoCheck queries GBIF for bat occurrence records across your search area, showing you which species have been documented, when they were last recorded, and the data source. This helps you determine whether a full mist-net survey is warranted or whether a habitat assessment alone may suffice.
Patrick O'Connor is a Freelance Ecologist at Kinterra Consulting and the developer of EcoCheck - an instant ecological desktop assessment tool for any location. Try it free at ecocheck.co (UK) or ecocheckus.com (US).