Globally, bats are intrinsic to healthy ecosystems, community integrity and vital ecological processes. They provide valuable ecosystem services (e.g., insect suppression, pollination, seed dispersal), products and provisions (e.g., tequila, durian, sisal, cactus fruits), cultural benefits (e.g., educational, recreational, spiritual) and contribute considerably to mammalian diversity. Notwithstanding, bats confront multiple threats. Habitat destruction and modification, climate change, pesticides and pollution, disease and human development (e.g., wind turbine facilities, urbanization) cumulatively contribute to population level impacts.  Additionally, roost availability and abundance are critical elements limiting chiropteran populations. As the availability and abundance of natural roosts decline, manmade infrastructure (e.g., mines, buildings, bridges, culverts) become incalculable substitutes. Highway structures function as comparatively permanent, alternative roosts (e.g., diurnal roosts, nocturnal roosts, maternity roosts) and stepping-stone refugia (i.e., transitory roosts) for migratory populations.  These anthropogenic structures proffer physical and thermal characteristics reminiscent of natural cavities (e.g., stable microclimatic conditions, predator protection) and proximity to elemental resources (i.e., water, optimal foraging sites).

State Departments of Transportation (DOTs) are increasingly incorporating environmental compliance, sustainability and stewardship within transportation planning, project development, construction, maintenance and operations. Furthermore, the exigency for environmental stewardship practices, procedures and policies echoes public concern for environmental integrity, habitat connectivity and biological conservation. Today, transportation authorities’ mission espouses the larger societal objective of environmental excellence and sustainable transportation [2]CitationAmerican Society of State Highway and Transportation Officials. 2016.. As such, consideration to wildlife movements (e.g., mammal collision mitigation measures), ecosystem impacts (e.g., establishment of replacement wetlands and habitat enhancement) and phenological timetables (e.g., stream crossings and fish spawning, bird incubation periods) are increasingly at the forefront of transportation planning.  Moreover, numerous states have become environmental champions, actively engineering and retrofitting highway structures to accommodate bat colonies.

Forty-seven microchiropteran species of 20 genera and three families populate the United States [40]CitationLoeb, S. C., T. J. Rodhouse, L. E. Ellison, C. L. Lausen, J. D. Reichard, K. M. Irvine, T. E. Ingersoll, J. Coleman, W. E. Thogmartin, J. R. Sauer, C. M. Francis, M. L. Bayless, T. R. Stanley, and D. H. Johnson. 2015. A plan for the North American Bat Monitoring Program (NABat). Gen. Tech. Rep. SRS-208. Asheville, NC; U.S. Department of Agriculture Forest Service, Southern Research Station. 100 pp. .  Of those species, 61.7 percent (29) and potentially 87.2 percent (41) exploit manmade transportation infrastructure (See Table 1); however, 100% may be vulnerable to activities that encompass a larger footprint.  To date, uncertainty exists regarding the type of survey and level of survey effort necessary, when to survey and how these decisions are affected by the habitat, time of year, geographical location and the species present or likely to be present within the prospective survey area [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. . To address these deficits, we have developed an empirically-based framework whereby transportation authorities can orchestrate bat mitigation, management and conservation initiatives. An extensive literature base including texts, journal publications, reports, proceedings, online databases and other synthesis documents and experiential information engender these progressive and inclusive best management practices (BMPs). Our objective was to produce comprehensive but practicable guidelines to harmonize transportation requirements with environmentally sustainable management practices.

North America’s transportation system encompasses ca. 13 million structures (i.e., > 6 m bridges, box culverts, drainage structures) that equate to approximately one construction per quarter mile (400 m). With potentially millions of linear “bat-friendly” footage, DOTs are an inadvertent cornerstone of bat conservation. DOTs provide thousands of artificial roosts per state, supporting an inestimable number of bats. Given the magnitude of present-day threats (e.g., white-nose syndrome, turbine collisions) and concomitant population declines, it has become increasingly important to minimize ancillary sources of mortality. Thus, DOTs can further safeguard our country’s remaining bat communities by implementing simple guidelines to minimize or eliminate adverse impacts from operational activities.

Operational activities that adversely affect bats primarily include roost destruction, modification of habitats and direct disturbance during critical life phases (i.e., maternity and weaning periods, hibernation).  Even those projects with uncomplicated scopes (e.g., pavement rehabilitation and reconstruction, bridge deck replacement, guardrail and fencing installation, timber treatment) and minimal environmental impacts may cause disturbance to resident colonies [7, CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. 27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp. . Additionally, landscape features are important habitat components; i.e., commuting routes, essential sources of insect prey and potential roosts for both crevice- and foliage-roosting species. Kelley [46]CitationNational Roads Authority. 2005. Guidelines for treatment of bats during the construction of national road schemes. Environmental Series on Construction Impacts, Dublin, Ireland, 8 pp.  maintains “the most significant impact of road construction upon bats is in the clearance phase of the scheme, namely tree- felling, the removal of hedgerows and other vegetation…”

This document provides standards by which to minimize the aforementioned impacts on bat communities. These BMPs emphasize surveys; humane evictionGlossaryeviction |iˈvikSH(ə)n| noun
the process or state of expelling; the employment of one-way devices whereby an animal leaves but cannot reenter and exclusion techniques; protocols for white-nose syndrome (WNS) decontamination; and avoidance, mitigation and compensation measures. Through these measures, we endeavor to provide informative, achievable guiding principles to assist transportation agencies with identifying and evaluating the potential and/or actual effects of a given project.  These principles advocate and facilitate animal welfare, consistency of approach and provide transportation authorities with site-appropriate strategies to minimize impacts to endemic bat populations. The ensuing recommendations demonstrate exemplar measures; thus, they may necessitate modification for feasibility, site specific differences, and project constraints (e.g., phase of development, available budget, conservation status of respective bat species).

Comprehensive information on the populations and distributions of the nation’s 47 bat species remains immensely deficient.  “For most species we have no knowledge of the size of populations and their demographic trends, the degree of structuring into discrete populations, and whether different subpopulations use spatially segregated migratory routes” [60]CitationVonhof, M. J., and A. L. Russell. 2015. Genetic approaches to the conservation of migratory bats: a study of the eastern red bat (Lasiurus borealis). PeerJ. 3:e983. . As such, this document relies considerably on references to international species, particularly European bats, which parallel those endemic to the United States – in appearance, life history requirements and roost selection. The indiscriminate decline of Europe’s bat populations and the respective legal responsibility of its constituent countries (i.e., national implementation of the EC Habitats Directive which protects all bat species, their habitats and roosts regardless of occupancy) prompt widespread scientific interest and conservation initiatives.  As a result, these countries contribute the most progressive and comprehensive volume of research and mitigation measures relative to the planning, design and implementation of national road schemes.  An inherent association exists between bridges, culverts and roads and thus, their standards provide an incredible foundation for these BMPs.

2 Structure Specific Misconceptions

The publication ‘Bats in American Bridges’ [31]CitationKeeley, B. W., and M. D. Tuttle. 1999. Bats in American bridges. Bat Conservation International, Inc., Austin, Texas. Resource Publication, 40 pp.  remains the authoritative work for bats and transportation structures.  Although this document provides an incredible wealth of information, people inaccurately consider their “ideal” characteristics as categorical requirements. This can precipitate misconceptions and erroneously influence surveyors or consultants and therefore, cause oversights with respect to bat occupancy. Bats exhibit considerable plasticity, both within and between species. Therefore, implementing a “one size fits all” approach to 29, and potentially 41, different bat species may effect devastating consequences. “While there are clear similarities among the different bat species, it is important not to generalize about them. What is possible for one bat species is impossible for another. In taking protective measures and undertaking construction planning it is generally advisable to take into account the most discriminating bat species” [38]CitationLimpens, P., P. Twisk, and G. Veenbaas. 2005. Bats and road construction. Ministerie van Verkeer en Waterstaat, Rijkswaterstaat, Dienst Weg-en Waterbouwkunde. 28 pp. .

3 Health and Safety Recommendations 

3.1 Occupational Safety and Health

Bat surveys can be arduous, involve challenging locations, severe time schedules, extensive travel and many potential hazards. These risks must be adequately considered and accounted for during survey planning. High risk sites include construction sites, enclosed spaces, remote locations, sites with criminal activities and/or hostile residents. Transportation structures may traverse or parallel watercourses, roads or railway lines, which increase hazard potential. Surveyors should be trained in safe working practices including tackling steep ground, climbing on ladders, and water safety (assessing water flow, depth and currents) and in the use of equipment such as waders, lifejackets/buoyancy aids, ladders and fiberscopes/borescopes.
Please employ appropriate caution and equipment to minimize safety risk.  Guidance on safety and risk management-related issues can be found @ OSHALinkVisit the Occupational Health and Safety Administration.

3.1.1 Speciality Training

The following locations require advanced knowledge and use of specialist equipment. Specialist training courses or permits may be applicable.

Confined Spaces

Confined spaces have limited or restricted means for entry or exit and are not designed for continuous occupancy. Please consult the OSHA Standard for Confined SpacesLinkVisit the Occupational Health and Safety Administration.

Trees 

Many tree roosts would be classified by an arboriculturist as hazardous because bats preferentially select older trees, with hollow limbs, rot holes or loose bark. Do not climb trees without the help of a ladder – tree climbing requires special training. Please consult the OSHA Standard for Portable Ladder SafetyLinkVisit the Occupational Health and Safety Administration.

At Height 

Work at height means work in any place where, if there were no precautions in place, a person could fall a distance liable to cause personal injury. Take a sensible approach when considering precautions for work at height. Before working at height, consider these simple steps; avoid work at height where it is reasonably practicable to do so; where work at height cannot be avoided, prevent falls using the right type of equipment; and minimize the distance and consequences of a fall by using the right type of equipment where the risk cannot be eliminated. Please review OSHA Fall Protection Standards and ResourcesLinkVisit the Occupational Health and Safety Administration.

3.2 Zoonoses

3.2.1 Rabies

Before working near known roosts, maintenance workers should be encouraged to avoid disturbing bats as much as possible, and taught not to handle them. These procedures will minimize the direct exposure of workers to bats and eliminate the possibility of personnel being bitten, which would then necessitate post-exposure rabies treatment. 

3.2.2 Histoplasmosis

Bird and bat guano are classic reservoirs for Histoplasma capsulatum, the fungus that causes histoplasmosis, a systemic infection primarily of the respiratory tract. Outbreaks have been associated with demolition and earth-moving activities that aerosolize topsoil and dust (e.g., bridge reconstruction and demolition, jack- and air- hammering, waste disposal). Employees should wear personal protective equipment and employ dust-suppression  techniques when working in areas potentially contaminated with bird and/or bat droppings [29]CitationHuhn, G. D., C. Austin, M. Carr, D. Heyer, P. Boudreau, G. Gilbert, T. Eimen, M. D. Lindsley, S. Cali, C. S. Conover, and M. S. Dworkin. 2005. Two outbreaks of occupationally acquired histoplasmosis: more than workers at risk. Environmental Health Perspectives, 113(5), 585-589. .

4 Decontamination Measures for White-nose Syndrome

WNS affects cave hibernating bats throughout eastern North America and adjacent Canada. This fatal disease continues to cause mass mortality and precipitous population declines. Previously common species throughout the northeastern United States are presently at risk of regional extirpation or extinction due to white-nose syndrome. “WNS has led to unprecedented mortality in several species of bats and may threaten more than 15 additional hibernating bat species if it continues across the continent” [22]CitationFlory, A. R., S. Kumar, T. J. Stohlgren, and P. M. Cryan. 2012. Environmental conditions associated with bat white-nose syndrome mortality in the northeastern United States. Journal of Applied Ecology, 49, 680-689..

Pseudogymnoascus destructans, the causative agent of WNS, thrives at temperatures of 3-15 ℃ and > 90% relative humidity, conditions equivalent to bat hibernacula and bodies of hibernating bats. P. destructans affects bats by increasing the frequency and duration of arousals from hibernation. Throughout the hibernation period, brief arousals to warm (euthermic) body temperatures are normal, but deplete fat stores. Typical arousal episodes span minutes or hours, with more frequent or lengthier arousal periods incurring significant energetic costs. Therefore, atypical arousal patterns due to white-nose syndrome prematurely deplete fat reserves crucial to overwinter survival. Additional WNS information available at whitenosesyndrome.orgLinkVisit whitenosesyndrome.org.

4.1 Decontamination Protocol

When activities involve close or direct contact with bats, their environments, and/or accompanying equipment and materials, please comply with decontamination protocols.  Acceptable treatment options and supplemental information are available from whitenosesyndrome.orgLinkVisit whitenosesyndrome.org.

5 Evaluative Surveys

Any construction, improvement or maintenance project can directly and/or indirectly impact bats via habitat destruction and fragmentation (i.e., loss or severance of traditional travel routes), landscape modification (i.e., influencing the suitability of roosting, commuting and foraging habitat), disturbance, and alteration of environmental conditions. Thus, transportation authorities should consider bats as part of the environmental assessment of any construction, improvement or maintenance project, regardless of scale [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp. . The practical implementation of bat conservation necessities standards by which to adequately ascertain potential impacts.

Surveys permits individuals to garner site-specific information by which to assess potential impacts and develop recommendations. Surveys are typically time-bound, once-only projects, although surveys may involve multiple visits or observations. These surveys are distinguishable from monitoring, which involves repeated sampling, either year-on-year or periodically, to evaluate whether a particular objective or standard has been attained [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. .

Surveys should identify existing and potential roost sites, map important foraging areas and record principal commuting routes. This valuable information facilitates a strategic plan to be formed to protect local bat populations. All bat surveys should be undertaken at the appropriate time of year to collate the information required (e.g., summer surveys to detect maternity roosts, winter surveys to detect hibernating bats). Surveys to document overall impacts should include right-of-way property; including land necessary for accommodation access, machinery, construction staging, and post-construction maintenance. Caves and mature trees proximate to sites have the potential for various roost types; including maternity roosts, transitional roosts, bachelor roosts, and hibernacula.  All species, including those that occupy nearby natural roosts, are vulnerable to poor watercourse management, and removal of treelines and vegetative cover (i.e., vulnerable to predators, open spaces are more lit, no protection from wind/rain).

Surveys must be sufficient to characterize the local environment and to provide defensible and robust impact predictions.  Any sites supporting bat colonies of considerable conservation value may require more exhaustive inspections and documentation.  This ensures the proper evaluation of impacts and mitigation measures.  To determine movements and the connection of critical areas, surveys may require a broader survey zone.  We recommend, when feasible, that comprehensive surveys identify the extent of all significant roosts and breeding sites within 1 km [46, CitationNational Roads Authority. 2006. Guidelines for assessment of ecological impacts of national road schemes. National Roads Authority, Dublin. 56 pp. 51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp.. To ensure reliability, several visits across biological seasons should occur (i.e., minimum of 2-3 times per year).  While bats are active throughout the night, peak activity occurs at dusk and before dawn; and surveyors should address bat activity during these time frames to provide comprehensive information of site utilization. The most effective detector survey period is June – August, which will provide information on maternity roosts. Earlier studies (April and May) and later studies (September) will yield information on alternative roosts [46]CitationNational Roads Authority. 2006. Guidelines for assessment of ecological impacts of national road schemes. National Roads Authority, Dublin. 56 pp..  Mist netting to capture and identify local bat species that may or may not be identifiable with bat detectors may be appropriate in certain circumstances (i.e., where detailed information on specific species is required, or where species of concern or high conservation value may occur).  In enclosed areas (e.g., bridges), harp-trapping may be employed to confirm the presence of species. (Please review Section 5.3 Survey Methodologies).

5.1 Surveyor Qualifications and Considerations

In the United States, there are no coincident standards nor specific qualifications to perform bat surveys. However, the assessment of bat presence requires expertise, experience and objectivity.  “It is comparatively easy to determine use of a site by bats, but absence is more difficult to prove. It requires greater effort to demonstrate beyond reasonable doubt that bats are not present or likely to be present [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. .”

Surveyors must be mindful and respectful, to prevent roost abandonment and accidental injury to or mortality of bats.  Additionally, the surveyor must be competent in identifying bats (may require capture and handling to determine/confirm species) and their respective habitat.  The specialist must be able to characterize the existing environment and evaluate its significance.  Where mitigation measures are necessary, the specialist must be capable of assisting the design and implementation of these measures.

To independently and competently conduct professional bat surveys, an individual should possess the following [8]CitationBat Conservation Trust. 2012. Professional Training Standards for Ecological Consultants. Bat Conservation Trust, London. 29 pp. ;

Expertise

• species status, distribution and conservation threats
• species-specific biology, ecology and ethology
• annual biological cycle and life history characteristics
• foraging strategies of different species
• physiology including adaptations to flight, echolocation, torpor, hibernation and energetics
• species-specific and seasonal requirements of roosts and the various natural features and anthropogenic structures available as roosts
• variety of available survey techniques, their appropriate application and limitations
• seasonality and conditions and their influence on surveys
• health and safety issues (e.g., unsafe structures, working at night)
• techniques to avoid and minimize negative impacts

Experience

• ability to identify sign(s), locate roosts and indicate probable species and roost type (e.g., maternity roost, night roost)
• capacity to identify habitats and roosts of importance within a landscape
• ability to assess appropriate survey level/effort
• ability to quantify potential impact(s) and deliver site- and species-specific recommendations for mitigation
• objectively assess the potential value of tree(s) or other structure(s) / feature(s) as bat roosts
• ability to capture, handle and/or transport individual bat(s) humanely and proficiently
• identify individual species and confidently age, sex and assess reproductive status
• communicate information and recommendations clearly and concisely

5.2.1 Desk Study (Pre-evaluation)

A desk study is the collation and analysis of currently available, relevant information. A desk study occurs within the early stages and will ascertain the type and intensity of further study. A preliminary landscape analysis (sources include Google Earth and EarthExplorer) can identify probable roost locations and landscape features favorable to the presence and/or transit of bats (e.g., mature forests, large trees, small fields, presence of water and watercourses) prior to site survey(s). Additionally, searches (e.g., natural resource databases, Smithsonian North American Mammals, International Union for Conservation of Nature, Map of Life distribution maps) performed prior to site surveys can provide information on the likelihood of vulnerable species being present (i.e., species of concern, T & E species). However, the absence of record(s) does not indicate the absence of species.
Where only minor impacts are foreseen, a simple assessment may initially be undertaken (See 5.2.2 Standard Survey) . Conversely, this exercise may indicate the potential for significant impacts, which warrants a detailed assessment (See 5.2.3 Advanced Survey). Chart 1 depicts the decision-making process and provides guidance on applicable survey level.

Objectives

Desk study objectives should include;

• delineate survey boundaries,
  Survey boundaries should encompass the development/disturbance footprint and an ‘area of influence’ that extends ≥1 kilometer from the project perimeter [6, CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. 23]CitationHolroyd, S. L., V. J. Craig, and P. Govindarajulu. 2015. Best Management Practices for Bats in British Columbia, Chapter 1: Introduction to the Bats of British Columbia. British Columbia Ministry of Environment, Victoria, British Columbia, 108 pp. . Note: Species-habitat relationships occur at varying spatial scales. Individual bat guilds are sensitive to distinct environmental factors and landscape pattern metrics. For example, Pipistrellus pipistrellus, a generalist species, demonstrates less strict selection of habitat components and prefers a high level of heterogeneity at a broader scale, acting as a “multiple-habitat” specialist. A more selective species, Rhinolophus hipposideros sensitive to small-scale habitat corridors (e.g., hedgerows) requires a high level of connectivity between habitat patches at a finer scale. Thus, for threatened or endangered species, multi-scale assessments may be necessary to adequately characterize habitat features and their spatial configurations that affect the abundance of populations or their assembly into local communities [16]CitationDucci, L., P. Agnelli, M. Di Febbraio, L. Frate, D. Russo, A. Loy, M. L. Carranza, G. Santini, and F. Roscioni. 2015. Different bat guilds perceive their habitat in different ways: a multi scale landscape approach for variable selection in species distribution modelling. Landscape Ecology, 30(10), 2147-2159.  
• identify potential species presence,
• evaluate habitat potential (presence and usage), and
• identify potential impact(s).

5.2.2 Standard Survey

An on-site visit can identify/confirm the potential importance or value of habitats and features. The resultant information identifies any prospective impacts and determines future survey objectives.  An assessment should include consideration of appropriate survey methods, survey intensity (i.e., level of effort) and proportionate footprint.

An exploratory survey to establish presence/absence, assess probability or severity of impact(s), and acquire information to recommend mitigation and/or compensation measures may include (See Appendix 3 for example data sheet);

General information

• date,
• surveyor name(s),
• site description (i.e., descriptive information and coordinates),
• proposed activity (e.g., construction, demolition, repair, maintenance),
• direct evidence of current or prior occupancy (e.g., guano, carcasses, cobweb-free entrances to voids, scratches, urine stains),
• species present,
• roost information including type (e.g., diurnal, nocturnal, maternity, hibernaculum), location, characteristics (e.g., crevice, swallow nest, drainpipe),
• intensity (e.g., number of bats, time and duration of use),
• roost substrate and dimensions,
• surrounding habitat (e.g., residential, agricultural, woodland), and
• conditions beneath roost (e.g., bare ground, railroad, watercourse, 4-lane highway).

Photographs are invaluable to conveying both structure-specific details and evidence of occupancy. It is recommended that photographs are taken to support written documentation. Please be mindful and responsible when photographing bats.

Built structure information

• structure design (e.g., type, number of spans, height),
• structure material (e.g., concrete, metal, timber), and
• location and description of current, prior or potential roost sites.

Trees information

These landscape features are important habitat components – commuting routes, valuable foraging areas, and potential roosts for both crevice- and foliage-roosting species. Most species exhibit high fidelity to roosts, foraging sites and the commuting flyways that connect them. Thus, maintaining a particular tree can be more consequential than for other vertebrate species. 

There are common principles by which to identify trees with suitable cavities and crevices and/or trees with the probable occurrence of bats, including characteristics of growth and decay and indications of activity.

There are two broad categories of transportation-specific tree works which can negatively impact bats;

• arboriculture – the physical maintenance and manipulation of trees, particularly for occupational safety and health, and aesthetics,
• development-related tree and woodland management – whereby the primary objective is to facilitate development.

Bat consultants and surveyors must possess specific experience with woodland and tree survey techniques. Surveyors must have basic comprehension of tree ecology and biology because relatively minor growth characteristics can indicate the presence of decay cavities or splits that may not be visible to inexperienced observers [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp.. 

• cursory inspection of natural structures and trees in proposed activity “footprint.”

5.2.3 Advanced Survey

Most sites will warrant standard surveys. However, where site-specific conditions or other findings suggest the potential for substantial adverse impacts to bats, advanced surveys designed to further evaluate specific concerns may be recommended. Thus, survey effort should be proportionate to survey purpose (i.e., to obtain adequate results for specific objectives) and may further identify;

• species whose distribution includes site (identify potential for species of conservation concern),
• any features of particular ecological or conservation significance,
• specific roost sites (confirmed and potential) that occur in close proximity to site;
• detailed inspection of potential tree roosts identified by standard survey,
• any watercourses, flyways, crossing points, or foraging areas that may be impacted by construction and clearance activities,
• potential site-specific mitigation, compensation or enhancement measures,
• colony type and sex. Sexual segregation does occur within habitats of various species. Therefore, the occupation of habitats by males/females should be identified. This may become important (e.g., impact the selection of trees for felling) because a site that sustains females would be more significant than one that support males,
• identify time of survey with respect to biological season. Bat activity may differ between certain periods due to variations in availability of prey, recruitment of juveniles, or the availability of suitable roost sites. For example, summer roosts may not provide the appropriate microclimates necessary for hibernation. Therefore, a survey done outside the breeding season may impart a false impression of the site’s importance,
• bat activity surveys; appropriate during warmer months (April – September) and at dusk emergence and/or dawn re-entry and may include documentation of active foraging and commuting habitats, emergence times and locations, intensity (estimate of population), species assessment via manual/automated bat detectors, and camera/video equipment (FLIR, infrared).

Survey effort must be commensurate to the extent of development and likely impacts. Surveys may require at least one year to evaluate seasonal differences and should be planned well in advance. 

5.3 Survey Methodologies

The objectives, location, habitat type and activity (e.g. roosting, foraging, commuting, mating, swarming or migrating) will determine the most appropriate survey method(s). Methods may typically involve one or more of the following; 

5.3.1.2 Visual Surveys
Bats may use transportation structures at any time of the year and timing of work must take into account bat activity at each site. It is not unusual for several bat species to use different parts of the same structure.

Bridges

Systematically search for direct evidence of occupancy. Inspect key features and locations likely to support bats. Roost locations may include;

• open beams,
• structural fissures (e.g., cracked or spalled concrete, damaged or split beams, split or damaged timber railings),
• crevices (e.g., expansion joints, space between parallel beams, spaces above supports piers, space between adjacent concrete parapets/guardrails),
• alternative structures (e.g., drainage pipes, bolt cavities, open sections between support beams), and
• nests. When abandoned or unoccupied, nests provide ancillary roost habitat for bats worldwide. Occupancy rates can approach 39 percent [30]CitationJackson, J. A., B. J. Schardien, C. D. Cooley, and B. E. Rowe. 1982. Cave myotis roosting in barn swallow nests. Southwestern Naturalist, 27(4), 463-464. . Bats that exploit Hirundo rustica (barn swallow) nests lay nearly prostrate within the nest cup and those within Petrochelidon pyrrhonota (cliff swallow) nests (gourd-shaped enclosed structures) are typically concealed and undetectable without a borescope or fiberscope.

Please note that bridges, like trees, often conceal bats within features not visible from the ground.

Culverts

Roost locations may include;

• walls,
• structural fissures,
• transition points between culvert sections (e.g., where a concrete culvert transitions to a metal culvert, where a box culvert transitions to a circular culvert),
• alternative structures (e.g., drainage pipes), and
• nests, particularly Hirundo rustica and Petrochelidon pyrrhonota nests.

Trees and natural crevices

The presence of bats in trees or geological features (e.g., rock formations, cliff faces, riverbank crevices) can be difficult without external signs (e.g., presence of guano, audible sounds).  Occupancy can be established by examination of suitable crevices, cavities, limb fractures, and loose bark. Specialist equipment (e.g., rope access, borescope) may be required in certain circumstances.

Certain characteristics denote potential tree roosts. Probability generally increases with tree age, size and presence of damage. Inspect any cavity ≥ 10 mm in diameter [24]CitationForestry Commission England, Bat Conservation Trust, Countryside Council for Wales, and English Nature. 2005. Woodland management for bats. Forestry Commission Publications, West Yorkshire, England. 16 pp. . Roost locations may include;

• coniferous or deciduous trees with evidence of decline or decay;
• damaged trees, irrespective of age (e.g., due to lightning);
• excavations by primary cavity nesters (e.g., woodpeckers);
• rot holes;
• cracks, splits, crevices;
• snags, various stages of deterioration;
• loose, peeling bark;
• basal cavities;
• hollow trees/trunks;
• standing dead wood;
• live or dead leaves (Lasiurus spp.);
• palm tree fronds (Lasiurus ega, L. intermedius, L. xanthinus); and
• Spanish moss (L. intermedius).

5.3.1.3 Emergence and Re-entry Surveys

Where potential presence is high, but cannot be confirmed, surveyors can perform dusk emergence and/or dawn re-entry surveys. Emergence and re-entry surveys can provide additional information (e.g., number of bats, species, flight paths to and from roost) to help determine the importance of an identified roost and potential significance of any impacts. Emergence surveys should commence > 15 minutes before sunset and continue for two hours after sunset [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. .
Dawn re-entry surveys can help detect summer roosts, particularly those of species who form small colonies, emerge late or are difficult to identify with bat detectors. Emergence and re-entry surveys should occur when bats are most active (April – September).
Dawn re-entry surveys of maternity roosts are oftentimes most successful July – August when re-entry attempts by newly volant juveniles are both obvious and of extended duration. These surveys should commence > 90 minutes before sunrise, as Myotis spp. typically return to roost sites earlier than other species.

5.3.1.4 Acoustic Surveys (active and passive)

Passive acoustic monitoring can identify periods and locations of peak activity levels. Automated activity surveys are non-intrusive and can help determine bat activity over lengthy time intervals; particularly winter (November – February), when bat activity is irregular. For winter activity, a minimum of two, two-week surveys sessions are recommended, one of which should occur between December and February [7]CitationBat Conservation Trust. 2007. Bat surveys: good practice guidelines. Bat Conservation Trust, London. 87 pp. . Various exogenous and endogenous factors influence activity patterns, which can further vary by habitat, season, species and locality (e.g., cool temperatures and precipitation typically suppress bat activity).

In more exceptional cases it may also be appropriate to use the more invasive survey techniques described below. Surveyors should employ non-invasive survey methodologies first and foremost.  The decision to employ invasive techniques may occur only where essential information cannot be acquired with less intrusive methods and must consider bat welfare and time-of-year vulnerability.

5.3.2 Invasive

• capture (i.e., hand nets, mist nets and harp traps)
• biotelemetry (i.e., radio-tracking)

Capturing bats via netting and harp traps can provide valuable information relative to species identification, sex determination and breeding status; and are necessary to adhere radio transmitters to individuals. Biotelemetry can provide further informative data on foraging areas and flyways and effectively pinpoint roost locations. Nonetheless, these techniques are invasive and warrant careful consideration. The minimum number of visits necessary to obtain the appropriate information will be situation and objective-dependent. Please prioritize animal welfare. If any method of capture causes, or appears to cause, distress or harm, please cease activities immediately and solicit further advice.

Time surveys to minimize the potential capture of parturient or lactating females; heavily pregnant bats may give birth or abort their fetus while captive [23]CitationFinnemore, M., and P. W. Richardson. 2004. Catching bats. In Mitchell-Jones, A. J., and A. McLeish, eds. 3rd Edition Bat Workers’ Manual. pp. 41-48. Joint Nature Conservation Committee. . Please become familiar with your state’s endemic bat species and their respective maternity seasons, which vary by species and region. Conservatively, refrain from conducting capture surveys from late May to mid-July, unless exceptional, and justifiable, circumstances exist.

These aforementioned methods should only be undertaken by specialist surveyors with prior demonstrable experience. 

5.4 Appropriate Time Schedules

Chiropteran ecology and ethology influence both timings of surveys and therefore, operational activities (See Figure 1 for an overview of the bats’ annual cycle). Bats exhibit considerable diversity and plasticity – both within and between species. Consequently, the annual cycle may vary. These biological milestones can further vary geographically; thus, optimal timings must develop from practical experience and familiarity with local species. All bat surveys should be undertaken at the appropriate time of year to collate the information required (e.g., summer surveys to detect maternity roosts and winter surveys to detect hibernating bats). 

5.5 Assessment

An evaluation of survey results and supplemental information are necessary to assess the importance of existing habitats/features, the magnitude of foreseeable impacts and their relationship to local bat populations. Impacts typically encompass habitat loss and degradation, severance of habitat features, disturbance and mortality. These impacts may be direct, indirect, permanent, temporary or cumulative. Assessments should include relative impact(s), their influence on the integrity and conservation status of relevant bat communities and recommendations for mitigation measures.

Depending on the magnitude and intensity of impact(s), populations are vulnerable to complete fragmentation, which can (i) reduce genetic diversity, thereby increasing susceptibility to extinction; and (ii) isolate subpopulations by decreasing interpopulation movement, thereby increasing the possibility of local population collapse [48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London..

5.5.1 Habitat loss and degradation
Habitat loss and degradation can have significant impacts on bat populations. Operational activities can have direct and indirect effects on roosts, foraging areas, commuting routes, prey abundance and important landscape elements. These effects may include;

• loss or degradation of habitats and fragmentation of remaining areas;
• disruption to local hydrology;
• physical/noise/light disturbance, which may affect roost viability;
• modification of roost microclimate, due to vegetation removal;
• impact to important foraging areas or existing roosts, due to tree removal;
• disturbance, injury or mortality of roosting bats; and
• delayed emergence or roost abandonment, due to nighttime lighting spillage onto adjacent foraging habitats or roosts [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp. .

Kerth and Melber [32]CitationKerth, G., and M. Melber. 2009. Species-specific barrier effects of a motorway on the habitat use of two threatened forest-living bat species. Biological Conservation, 142(2), 270-279.  attribute lower reproductive success and smaller foraging areas of female Myotis bechsteinii to a major roadway that restricted habitat accessibility. In bats, both reduced reproductive success and increased mortality will profoundly affect local colony size and overall population size. 

5.5.2 Severance of habitat features

Bats employ a tapestry of roosts, flight paths and foraging areas within the landscape. These routes parallel linear landscape elements including treelines, hedgerows, minor roads, tree canopies, watercourses and ditches. The ecological function of linear features include (i) navigational guide, (ii) foraging potential and (iii) weather/predator avoidance. Both permanent and temporary severance of these habitat features may therefore, cause major impacts to bat populations. Severance may cause barriers to movement, thereby restricting access to critical resources and disrupting foraging activity. Level of use, species involved, availability of alternative habitat and features, and degree of impact (i.e., permanent or temporary) will influence the potential significance of the severance.

The severance of linear features can be caused by,

• operation and construction of new roadways,
• removal of habitat features due to highway maintenance; and
• improvements and/or widening of existing roadways and associated infrastructure.

Near maternity roosts, severance becomes more consequential, as reproductive females and young (i.e., critical sectors of the population) are affacted [12, CitationBickmore, C. 2003. Catherine Bickmore Associates. Review of work carried out on trunk road network in Wales for bats. A report produced on behalf of the Transport Directive, Welsh Assembly Government & Countryside Council for Wales. 48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London. . “This could have an effect on the favourable conservation status of the species locally and may also have wider implications for the species at a regional and possibly national level dependent on the rarity of species concerned” [48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London. . 

5.5.3 Disturbance

Installation of temporary or permanent lighting can introduce barriers to movement, sever foraging areas, discourage emergence or precipitate roost abandonment. Roost adjacent lighting may modify microclimatic conditions (i.e., humidity or temperature) or cause disturbance, which may precipitate roost abandonment. Similarly, maintenance projects can potentially disturb roosting bats via employment of inappropriate methodologies or materials, or modification of roost parameters.

5.5.4 Mortality

Mortality may occur from reactive behavior, traffic differences, or accidental roost
destruction. Some species may continue to follow severed commuting routes, endangering those individuals that traverse roadways. Anecdotal observations [12, CitationBickmore, C. 2003. Catherine Bickmore Associates. Review of work carried out on trunk road network in Wales for bats. A report produced on behalf of the Transport Directive, Welsh Assembly Government & Countryside Council for Wales. 27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp. indicate that “air turbulence caused by fast and large road traffic can suck nearby bats into the path of oncoming vehicles.” Traffic inflation, resulting from improvements or new construction, may cause significant mortality, particularly when adjacent to nursery roost(s), with inexperienced juveniles most vulnerable. Mortality rates increase during July and August, coincident with the occurrence of volant young; and late September – early October, which may correlate to mating and autumnal migration [31, CitationLesiński, G. 2007. Bat road casualties and factors determining their number. Mammalia, 71(3), 138-142. 25, CitationGaisler, J. Z. Řehák, and T. Bartonička. 2009. Bat casualties by road traffic (Brno-Vienna). Acta Theriologica, 54(2), 147-155. 36, CitationLesiński, G., A. Sikora, and A. Olszewski. 2011. Bat casualties on a road crossing a mosaic landscape. European Journal of Wildlife Research, 57(2), 217-223. 41]CitationMedinas, D., J. T. Marques, and A. Mira. 2012. Assessing road effects on bats: the role of landscape, road features, and bat activity on road-kills. Ecol Res, 28, 227-237. .

5.6 Documentation

An assessment report should include,

• information from collective survey(s) including important habitat features (e.g., existing roosts, foraging areas, commuting routes) species present, et cetera and their relative importance;
• the potential effects of the relevant operational activity;
• recommendations for mitigation and an explanation and/or justification for selecting these recommendations;
• recommendations to prevent, reduce and as fully as possible offset any significant adverse effects; and
• monitoring methods and protocols, if applicable.

6 Mitigation Measures

This section provides mitigation measures by which to avoid, minimize and if possible, remedy adverse effects. Where elimination of adverse effects is not possible, measures can be implemented to alleviate the severity of impacts. Species differ relative to sensitivity and exploitation (e.g., roost choice, travel corridors, flight heights, foraging strategy) of the landscape. Therefore, any mitigation measures should endeavor to accommodate the species with the most sensitive requirements or conservation
status. Mitigation measures must be project-specific, and proportionate to the importance of population(s) and scale of potential impacts. If in-situ mitigation is not possible, off-site habitat creation and enhancement of existing suboptimal habitat should be considered.

6.1 Avoidance

Avoid disturbing sites while bats are present whenever possible. Avoid permanently destroying/altering bat roosts whenever possible.  Avoidance of an area, structure, or site with bat presence remains the best mitigation measure for the protection of bats. Many roosts are seasonal and therefore, operational activities may occur within the period when bats are absent.

Optimum season for operational activities for different roost types are as follows;

• for maternity and nursery roosts, conduct activities 1 October to 1 May
• for summer roosts, conduct activities 1 September to 1 May
• for hibernacula, conduct activities 1 May to 1 October
• for swarming / mating sites, conduct activities 1 November to 1 August

Please become familiar with your state’s endemic bat species and their specific biological seasons, which vary geographically. 

6.2 Minimization

6.2.1 Appropriate Time Schedules

Bennett et al. [10]CitationBennett, F. M., S. C. Loeb, M. S. Bunch, and W. W. Bowerman. 2008. Use and selection of bridges as day roosts by Rafinesque’s big-eared bats. Am. Midl. Nat., 160(2), 386-399.  recommend an inspection interval of 3-5 times annually to determine use. Lengthy time intervals between biological investigations and construction increase the probability of occupancy; and therefore, the unreliability of those evaluations.
Maternity colonies form from April onwards and remain relatively cohesive through mid- to late August. Young, born May-July, are non-volant (i.e., not capable of flight or evasive action, wholly dependent on mothers) for several weeks and thus, are extremely vulnerable to disturbance by human activities (e.g., restoration, reinforcement or demolition of structures).
Please become familiar with your state’s endemic bat species and their respective maternity seasons, which vary by species and region. Contact your state wildlife agency to learn specific details about time-of-year restrictions, regulations, sensitive species (T & E species, state species of concern) statutes and/or requisite permits. Please note, the minimum standards provided here may not be sufficient to avoid, minimize, or mitigate impacts to listed bat species.

6.2.1.1 Wildlife Exclusion

Specific mitigation measures to exclude must be in situ prior to demolition or maintenance activities.

Exclusion practices to prohibit migratory birds with ≥ 3/4” netting does not exclude bats. Any indication of bats necessitates the appropriate installation of 3/8” netting. If bats are present, installation should not occur April – August when bats are exceptionally vulnerable to disturbance. If hibernating bats are present, installation can not occur late November – early March.
Bats can be excluded with one-way valves, professional sealants and/or 3/8” exclusion netting. One-way devices (e.g., tubes, cones, mesh) permit bats to exit but not re-enter the structure(s). Exclusion may occur September – March. If bats are present, installation of one-way valves must occur prior to netting. Winter exclusion must entail a survey to confirm either, 1. bats are absent or 2. present but active (i.e., continuously active – not intermittently active due to arousals from hibernation).
Application of sealants without prior surveying or professional exclusion can entomb bats. We therefore advocate the preclusion of sealants unless a qualified consultant confirms the absence of bats.

Any exclusion product may cause disturbance, harm or fatality if improperly installed. It is the responsibility of the hiring agency to ensure anyone performing these activities is knowledgable in the appropriate and humane application.

Please respect wildlife. Do not poison, pressure wash, trap, relocate, or in any other manner harm, harass or kill bats. These are ineffective, unnecessary techniques, potentially illegal, and do not comply with acceptable standards. 

6.2.1.2 Maintenance

Maintenance activities include, but are not limited to, cleaning, preventative maintenance to preserve and lengthen service life, technical and specialized repairs and stream channel maintenance. These activities may involve the operation of support vehicles and equipment, pavement repair, welding and grinding operations, and associated pollutants, which may impact nearby bat colonies.

Minor maintenance activities (e.g., wing wall repair or underpinning foundations) typically have minor or no impact on bats. However, more substantial maintenance operations, including replacement or strengthening of structures above water level, should entail a bat assessment [6]CitationBat Conservation Ireland. 2010. Bats and waterways. Guidance notes for planners, engineers and developers.. If bats are present, exclusion procedures should be implemented prior to maintenance activities.

Some maintenance activities (e.g., sealing cracks and crevices) may entomb bats or cause the abandonment of non-volant young. Additionally, these activities can create excessive noise, vibrations, and modify thermal conditions of roosts; and consequently, may promote roost abandonment. If bats are present, exclusion procedures should be implemented prior to maintenance activities.

Night-time maintenance activities can affect bats. Light, odors and noise can delay or discourage bats from emergence, or potentially, cause site abandonment. Activities adjacent to flyways and roosts should be avoided, especially when bats are most vulnerable (mid-March – end of July). If operations are inevitable, we recommend the installation of very localized lighting in the worksite zone, avoiding surrounding areas to reduce the barrier effect. The temporary erection of noise barriers and/or light screens may also be considered. Temporary infrastructure (e.g., stockpile areas, roads for construction traffic) should be constructed at a distance from roosts [51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp. .

Vibrations from noise disturbances within 0.8 km of a known or suspected hibernaculum may cause arousal from hibernation. The disturbance to hibernating bats reduces the probability of survival because arousals and the return to euthermy depletes imperative fat reserves (i.e., energy supply).

Maintenance activities which involve the replacement of bridge components with contrastive products may modify roost microclimate, dimensions, illumination, et cetera; and consequently, may promote roost abandonment.

6.2.1.3 Clearance Activities 

Keeley [45]CitationNational Roads Authority. 2005. Guidelines for treatment of bats during the construction of national road schemes. Environmental Series on Construction Impacts, Dublin, Ireland, 8 pp.  asserts “the most significant impact of road construction upon bats is in the clearance phase of the scheme, namely tree-felling, the removal of hedgerows and other vegetation..” These landscape features are important habitat components for insectivorous bats.

Tree management

Tree-felling can occur 15 September to 30 November, and 15 March to 15 April. These months coincide with periods of volant young and hibernation, with the assumption that bats are not hibernating within the site footprint. Please consider weather fluctuations and geographical location for appropriate time schedules.

Immediately prior to felling, potential roost trees (e.g., trees with snags, cavities, exfoliating bark) should be examined for presence/absence of bats and/or other bat activity. Bats rarely roost openly, and are most commonly present within tight spaces and crevices; therefore, a borescope or fiberscope may be necessary for definitive presence/absence. The National Roads Authority [46]CitationNational Roads Authority. 2006. Guidelines for assessment of ecological impacts of national road schemes. National Roads Authority, Dublin. 56 pp.  further recommends a nighttime detector survey, which should occur from dusk through dawn to ensure that bats do not re-enter the tree. An inspection “confirms the status of the tree only at the time of inspection and where there is a delay of one day or greater the tree must be re-assessed.” If bats are present, felling should not occur 15 April – 15 September to ensure the protection of maternity colonies and non-volant juveniles.

If possible, do not fell any trees with potential roosts from 1 May to 31 August (possible occurrence of maternity colony) and 1 December to 14 March, due to the possible occurrence of a maternity colony, and hibernating bats, respectively.

Tree removal activities within .8 km of a known or suspected hibernaculum can occur between 15 November and 15 March and between 15 September and 15 March within 16 km of the hibernaculum [57]CitationUnited States Fish and Wildlife Service. 2007. Biological opinion on the Ohio Department of Transportation’s statewide transportation program for the federally-listed endangered Indiana bat (Myotis sodalis). US Fish and Wildlife Service, Ohio Ecological Services Field Office, Reynoldsburg. 55 pp. .

If exclusion procedures must be implemented, a bat specialist can provide direction relative to the necessary actions and appropriate time periods. If a roost tree must be felled outside the optimum season, the specialist must endeavor to remove any bats to safety. Live bats may be released once all tree-felling has concluded.

If tree felling must occur, the tree should be checked carefully for signs of bat occupancy. A bat specialist can endeavor to facilitate the capture of individual bats. Once felled, the roost can be cut out and strapped to a nearby, sound tree in a similar situation to its original position. If bats are in a crack of a branch kept open by stress, care must be taken when cutting so that the crack does not close and crush the bats. Holes may harbor bats so care must be taken not to cut into, or directly above them. Bat roosts within hollow branches that must be removed can be relocated and attached to another tree via heavy duty webbing [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp..

We encourage the implementation of mitigation measures to compensate for the loss of tree roosts (See Section 6.3 Compensation).

6.2.2 Protection of proximate roosting / foraging habitat

Those species that exploit transportation structures may benefit from proximate tree cavities and natural rock crevices. Therefore, clearance activities within the right-of-way may cause the destruction of secondary roosts and diminish habitat integrity (e.g., loss of foraging areas and structures that compose flyways). “A break, even a few metres long, in the linear structures that form flyways is likely to reduce or prevent access to foraging areas or more remote roosts” [51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp. .

The removal of trees and vegetation decreases the availability and abundance of foraging habitat and provisional roosts for individuals occupying structures, as well as, local bat assemblages that select trees as primary roost sites. Linear landscape features form an important component of the commuting routes for bats, as well as essential foraging sites. Hedgerows and treelines function as “roads,” and migration or long-distance flights may be dependent on these discernible landscape features. The USFWS [57] CitationUnited States Fish and Wildlife Service. 2007. Biological opinion on the Ohio Department of Transportation’s statewide transportation program for the federally-listed endangered Indiana bat (Myotis sodalis). US Fish and Wildlife Service, Ohio Ecological Services Field Office, Reynoldsburg. 55 pp. proposes the protection of land via conservation easement or deed restriction to offset the loss of suitable habitat, particularly near waterways / riparian areas. We advocate native tree plantings to create future habitat and travel corridors and restore connectivity and landscape permeability. Additionally, the control of invasive plant species can further create quality habitat.

Where trees of importance to bats are situated along the periphery of the construction footprint, the potential of retaining these trees should be outlined within the deliverables and discussed with relevant personnel prior to site clearance [45]CitationNational Roads Authority. 2005. Guidelines for treatment of bats during the construction of national road schemes. Environmental Series on Construction Impacts, Dublin, Ireland, 8 pp. .

If possible, retain treelines and vegetation adjacent to watercourses. Confine operational activities on watercourses to one side of the channel to minimize damage to the wildlife corridor. Protect and identify with tags, flags, et cetera, trees and shrubs to be retained during operational activities.

Implement a management scheme where removal of important trees and shrubs are replanted with similar or native species within the same year of activities. To minimize the potential for vehicle collisions, roadside plant species should not attract insects and hence, indirectly bats. Sétra [51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp. recommends an approximately 10 m wide strip without woody vegetation on either side of the roadway. 

6.2.3 Vegetation Removal

Bats orient themselves by, and fly parallel to, linear landscape elements; including tall vegetative cover, transition zones (i.e, edge habitat), minor roads and waterways. Bats exploit these linear features to locate and capture prey and to safely commute between roosts and feeding areas.  The removal of vegetative cover and treelines, loss of mature trees and disturbance of wetlands all affect the availability of vertebrate prey and foraging sites for bats.  A gap of 10 m or more may cause some species to abandon both the commuting route and roosting site [15, CitationEntwistle, A. C., S. Harris, A. M. Hutson, P A. Racey, A. Walsh, S. D. Gibson, I. Hepburn, and J. Johnston. 2001. Habitat management for bats: a guide for land managers, land owners and their advisors. Joint Nature Conservation Committee, Peterborough, UK. 5]CitationBat Conservation Ireland. 2010. Bats and waterways. Guidance notes for planners, engineers and developers. .

6.2.4 Lighting

Light pollution effects ecological interactions across various taxa and can negatively affect critical behaviors. Obligatorily nocturnal species, i.e. bats, are particularly sensitive to artificial illumination, which can influence behaviors such as foraging and commuting, emergence, roosting, breeding and hibernation. Artificial lighting can sever commuting routes from roosts, via light spillage, onto hedgerows and watercourses. Such disturbance disrupts the ecological functionality of the landscape by creating barriers to effective animal movement.

According to Morrison [43]CitationMorrison, D. W. 1978. Lunar phobia in a neotropical fruit bat, Artibeus jamaicensis (Chiroptera: Phyllostomidae). Anim. Behav. 26, 852-855. and Fenton et al. [21]CitationFenton, M. B., N. G. H. Boyle, T. M. Harrison, and D. J. Oxley. 1977. Activity patterns, habitat use, and prey selection by some African insectivorous bats. Biotropica, 9, 73-85., light intensities as minimal as moonlight may reduce bat foraging behavior. While light sensitivity varies by species, microchiropterans generally exhibit a higher tolerance of red visual light than white light [6]CitationBat Conservation Ireland. 2010. Bats and waterways. Guidance notes for planners, engineers and developers.. Some species abandon traditional commuting routes when illuminated by either high-pressure sodium (orange) or light emitting diode (‘LED,’ white) street lights, which can deter bats from reaching their preferred foraging habitat [54,CitationStone, E. L., G. Jones, and S. Harris. 2009. Street lighting disturbs commuting bats. Current Biology 19, 1123–1127. 55]CitationStone, E.L., G. Jones, and S. Harris. 2012. Conserving energy at a cost to biodiversity? Impacts of LED lighting on bats. Global Change Biology, 18, 2458–2465.. Experimental illumination alters obstacle avoidance capabilities of Myotis lucifugus [49]CitationOrbach, D. N., and B. Fenton. 2010. Vision impairs the abilities of bats to avoid colliding with stationary obstacles. PLoS ONE, 5, e13912.. A maternity roost of 1000-1200 Myotis emarginatus was abandoned after lighting spilled directly onto the entrance [13]CitationBoldogh, S., D. Dobrosi, and P. Samu. 2007. The effects of illumination of buildings on house-dwelling bats and its conservation consequences. Acta Chiropterol. 9, 527-534. . Myotis lucifugus and Eptesicus fuscus numbers declined by 53-89 percent and 41-96 percent respectively, after installation of incandescent lamps (40 and 60 watts), cool fluorescent lamps (40 watts) and spotlights (150 watts) inside nursery roosts [35]CitationLaidlaw, G. W. J., and M. B. Fenton. 1971. Control of nursery colony populations of bats by artificial light. J. Wildl. Manage. 35, 843-846.. Species-specific responses can differ due to biological season (e.g., for Myotis grisescens, increased travel distances to foraging areas for lactating females suppress juvenile growth rates; [56]CitationTuttle, M. D. 1976. Population ecology of the gray bat (Myotis grisescens): Factors influencing growth and survival of newly volant young. Ecology, 57, 587–595.), distance to alternative routes (e.g., commuting costs become prohibitive for Pipistrellus pipistrellus when foraging areas are > 5 km from the roost; Speakman et al. 1991), flight morphology and echolocation (i.e., fast-flying species that employ long-distance echolocation systems regularly forage around street lamps; [50]CitationRydell, J. 1992. Exploitation of insects around streetlamp by bats in Sweden. Funct. Ecol. 6, 744-750.) and predation risk (i.e., higher light levels increase exposure to visual predators). Lighting can modify bats’ roosting sites, commuting routes and foraging areas, particularly along waterways. Bats commute and forage along dark wildlife corridors (e.g., rivers, canals) and consequently shy away from highly illuminated sections. Therefore, illuminated structures can impede their flight to suitable feeding areas.

Lighting along waterways should be avoided at all times. In addition, buffer zones (i.e. dark zones) should be included adjacent to waterways. Intensely lit areas may impair bats’ vision and cause disorientation, inhibit movements and prevent access to roosts and foraging areas. Illuminated roosts may cause abandonment or delay emergence. This can reduce foraging times (i.e., miss peak levels of insect activity, decrease foraging bouts) and thus, body weight, reproduction and winter survivability. Therefore, it is essential that lighting plans for a development site and around known roosts take into consideration the exit points, flight paths and foraging areas for bats and ensure these areas are not illuminated. However, light intolerance can be beneficial to dissuade some species from using customary commuting routes that cross traffic and thus, increase the potential for bat-vehicle collisions. Lights positioned close to identified crossing points can deter bats when placed at 10 m intervals.

Different light types presumably have different effects, and these effects may be species- and behavior-specific. Choice of light type, and hence its spectral distribution, will inevitably be a compromise between wildlife and public requirements. However, potential negative impacts on light-averse bats and insects can be minimized by avoiding short wavelength “blue” lights [20]CitationFalchi, F., P. Cinzano, C. D. Elvidge, D. M. Keith, and A. Haim. 2011. Limiting the impact of light pollution on human health, environment and stellar visibility. J. Environ. Manage. 92, 2714-2722.. To mitigate negative effects, artificial light should be restricted to “(i) where it is needed, (ii) when it is needed, and to (iii) an illumination level that achieves its purpose but does not exceed it” (Lewanzik and Voigt 2014). Planning conditions to minimize disturbance include;

• hours of illumination (i.e., provide some hours of darkness),
• light levels (i.e., install lighting that complies with the lowest light levels necessary for human health and safety),
• light height (i.e., reduce the amount of light spillage where it is not needed by restricting the height,
• directional lighting (i.e, direct light to only where necessary to prevent light spillage; position lights to avoid sensitive areas, particularly roost exit points); internal and external louvres can reduce light spillage by ≤ 97% [18]CitationEmery, M. 2008. Effect of street lighting on bats. URBIS Lighting Ltd..

Best practice for minimizing light impacts include [6]CitationBat Conservation Ireland. 2010. Bats and waterways. Guidance notes for planners, engineers and developers.;

bat roosts 

• no direct illumination, particularly on exit points
• position lights to avoid sensitive areas
• employ low pressure sodium or high pressure sodium lights
• avoid the employment of mercury or metal halide lamp
• restrict hours of illumination
• restrict lights to maintain/create dark zones (i.e., establish ‘darkness corridors’ to enhance fragment connectivity)

foraging and commuting routes

• avoid lighting along watercourses
• avoid lighting along important commuting routes
• avoid the employment of mercury or metal halide lamps
• minimize light spillage with shields, masks and louvres
• maintain light columns as low as possible
• restrict lights to maintain/create dark zones

6.3 Compensation

Where impacts cannot be avoided or lessened, it may be possible to compensate for these impacts or restore some aspect of the natural environment to an approximation of its previous condition (e.g., planting of native trees and shrubs to compensate for the loss of hedgerows or woodland; habitat creation in areas adjacent to the road, including wetlands; connecting bridges or passages to help link fragmented habitats). Consideration should be given to the presence of existing important roosts and proximate foraging habitat. A coherent network of roosts, habitats, and flyways should be retained to ensure the viability and favorable status of populations [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp..

O’Connor et al. [48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London.  note, “… given the relatively little time that bats have been such an important consideration and only the relatively recent advent of detailed bat surveys using developing technologies in bat detectors and recording devices, some of this mitigation has been designed and built based on the best available general knowledge and understanding of bat activity to predict how bats may react to such mitigation, rather than on actual results of specific highway severance mitigation examples or research.”

Consistent and scientific analyses of mitigation measures are immensely deficient. The development of best practices for mitigation necessitates pre- and post-implementation monitoring.  We recommend sufficient, comprehensive surveys to gather ‘best available information’ on structure (i.e., type of mitigation measure, dimensions) implementation, successful elements (e.g., landscaping), environmental considerations (e.g., land-use, lighting), et cetera. Continual monitoring of temporary mitigation can inform development/modification of permanent migration, including the design or placement of mitigation structures [48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London.  .

6.3.1 Provision of habitat features

Important habitat features include;

• natural roosts,
• foraging resources (i.e., areas supporting insect populations),
• linear features (e.g., hedges, treelines, waterways), and
• connectivity between habitats and roosts.

“Bat species can differ as much from one another as a swallow does from a mallard” [38]CitationLimpens, P., P. Twisk, and G. Veenbaas. 2005. Bats and road construction. Ministerie van Verkeer en Waterstaat, Rijkswaterstaat, Dienst Weg-en Waterbouwkunde. 28 pp. . Despite both inter- and intra-specific differences, bats generally exploit landforms as a ‘network in the landscape.’ There exists an elegant system of roosts, flight paths and foraging areas; with different aspects of the landscape fundamental to different biological requirements (e.g., summer roosts, hibernacula, ponds and watercourses). To adequately compensate for lost or fragmented habitat, one must consider these important components of “bat habitat”. 

6.3.1.1 Foraging Areas

Development of small-scale landscapes with heterogeneous structure can compensate for lost foraging areas. Limpens [38]CitationLimpens, P., P. Twisk, and G. Veenbaas. 2005. Bats and road construction. Ministerie van Verkeer en Waterstaat, Rijkswaterstaat, Dienst Weg-en Waterbouwkunde. 28 pp.  recommends the development of comparable or superior feeding habitat or landscape with similar or larger dimensions. It is important to create and maintain a landscape as permeable as possible.

6.3.1.2 Linear Features

Various strategies are currently available to mitigate for the severance of flyways/dispersal routes including;

• the manipulation of linear landscape features,
  Employ existing linear features or create flyways (e.g., plant hedgerows) to guide bats toward safe crossing points, including realignment away from dangerous crossing points. Temporary flyways (e.g., cut trees, in barrels of sand, with mesh ribbon to mimic leaves, placed before nightfall along flyways crossed by the working area) [27] CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp. can be used until permanent replacements are in situ or vegetation has matured.
• increasing the height at which bats traverse roadways, and
  Encourage bats to fly higher over roadways with fences, tree planting, et cetera (e.g., hop-overs).
• provision of crossing structures.
  In addition to increasing the height of flyway approaches, structures can be used to maintain bats at height as they cross the road or allow them to cross under the road. Examples include green bridges, lighting columns and culverts.

6.3.1.3 Crossing Structures

Crossing structures are site-specific movement corridors positioned over roadways that bisect important habitat and include underpasses, overpasses and hop-overs. In determining structure design, consider the following points [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp.;

• cost effectiveness, e.g., combining with other compatible uses, such as pedestrian bridges and watercourse/culverts can minimize cost;
• position structures along the line of existing flyways and connect to adjacent landscape features, e.g., hedgerows, treelines;
• shorter span structures may be more successful;
• structures should not be lit; and
• determine design by reviewing current best practice information.

Where using existing structures is not possible, consideration can be given to purpose built crossing structures, noting the uncertainty of their effectiveness [27]CitationHinde, D. 2008. Nature conservation advice in relation to bats. Highways England Interim Advice Note 116/08. 57 pp.. Underpasses are applicable particularly where a new road is carried upon a raised embankment allowing insertion of a tunnel (culvert) beneath the road, or the topography allows the building of a bridge over a hedge, stream or other feature that represents an existing flight line (Altringham 2008). The consensus relative to width is “the wider the passage the more it will be used by bats” [51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp. . A height of 4.5 m and width of 4 – 6 m has been recommended to ensure accessibility for all species.  The optimal size for culverts is 3 m, with a minimum of 1.5 m.
Underpasses, and overpasses, benefit bat species by permitting them to cross roadways close to established commuting points [51]CitationSétra, CETE de l’Est, and CETE Normandie-Centre. 2009. Bats and road transport infrastructure - threats and preservation measures. Sétra Information Notes, Economics Environment Design Serie n 91, 22 pp. .  In certain circumstances, these structures offer a solution to facilitate movement from nearby roosts to foraging areas and alternative roosts.  To encourage employment of these structures, plantings should direct bats towards the bridge or underpass; bats instinctively follow these linear elements to crossing points. Planting of linear  corridors should happen early in the construction phase and, where possible, should comprise relatively mature plants, both to ensure these are established quickly and, ideally, so that bats discover these routes before project completion. Valuable treelines or vegetation loss during the clearance phase can be detrimental to bat communities. The installation of hedges/shrubs can direct bats to safe crossing points.  However, the time requirement for plants to grow reduces the effectiveness of this measure. Temporary netting or fencing can therefore be installed to avoid gaps (See Figure 2). 

Overpasses, when connected to landscape structures, can also direct bats over roadways. The addition of plants along the length of one side, or an opaque windbreak (between 1.5 m and 3 – 4 m) may further enhance this measure (Figure 3).
In Europe, green bridges – overpasses with vegetation – were traditionally for medium to large mammals [48]CitationO’Connor, G., R. Green, and S. Wilson. 2011. A review of bat mitigation in relation to highway severance. Highways Agency, London.. In recent years, however, evidence indicates that bats exploit green bridges as guiding features similar to hedges and rows of trees (See Figure 3). Simple removable overpass structures consist of wires or wire netting stretched horizontally between two masts on either side of the roadway.  These may be installed either temporarily, to appraise the suitability of a location before installing more substantial structures or as a permanent mitigation measure (Figure 4). 

A hop-over consists of dense vegetation (e.g., trees, shrubs) or other materials (e.g., wood, wire netting, mesh wire with climbing vegetation) planted on either side of a road with overhanging branches that create a continuous canopy above the roadway (Figure 5).  Limpens [38]CitationLimpens, P., P. Twisk, and G. Veenbaas. 2005. Bats and road construction. Ministerie van Verkeer en Waterstaat, Rijkswaterstaat, Dienst Weg-en Waterbouwkunde. 28 pp.  provides recommendations for hop-overs; however, few studies examine their effectiveness. Hop-overs are typically created by means of tall trees or 6 m high wire netting with dense low vegetation to encourage bats to fly higher. 

General recommendations include;

• for high-flying species, the crowns of existing trees on either side of the road should meet to maximize success
• for relatively low-flying species, it may be necessary to plant dense thickets up to 6 m high to force bats to fly higher
• where the flight path is being used by species that will fly through clutter (e.g., vegetation), it may be necessary to use a wooden screen/mesh 4-5 m high with the addition of lighting at the hop-over location. The lighting must illuminate the road, but not the surrounding area.

The requisite for specific measures to mitigate fragmentation and the successfulness of these measures appears to vary between species, possibly due to factors such as flight pattern and foraging behavior. Other location-specific factors may influence the approach to mitigation provision, including; 

• proximity to features that contribute to life phases (i.e., seasonal activity or
  behavior) critical to survival or reproduction (e.g., roost sites); and
• proximity to features that facilitate foraging or movement (e.g., watercourses, vegetation).

6.3.1.4 Alternative roosts

Independent roosts

Where sizable roost(s) are lost, alternative structures (i.e., bat houses, boxes) can be built to expiate these impacts. The structure should adequately support the displaced colony with respect to roost size (internal dimensions should correspond to target species), thermal value (i.e., traditional wooden bat boxes do not replicate the thermal dynamics of concrete or thick beam timber bridges). Where bat roosts in bridges are lost due to demolition, rebuilding or engineering constraints, new roosting sites should be created within the structures, duplicating the original crevice dimensions [42]CitationMitchell-Jones, A. J. 2004. Conserving and creating bat roosts. In Mitchell-Jones, A. J., and A. McLeish, eds. 3rd Edition Bat Workers’ Manual. pp. 41-48. Joint Nature Conservation Committee. .

This measure should also include suitable boxes to satisfy the general requirements of different bat species present year-round.  Alternative roosts may provide critical short-term roosting opportunities and should be employed to complement any mitigation measures to protect roosts.  The installation of alternative roosts may reduce the impacts to local bat populations and provide safe roosting sites for colonies where natural sites are not available.

The erection of these roosts should be initiated prior to commencement of operations (site construction / demolition) and must be appropriately sited (adjacent to suitable foraging areas). Boxes should be monitored for acceptance and seasonal occupancy, and those that remain vacant for > 2 years should be relocated. Boxes should be installed on bridges with soffit > 1 m above highest recorded water levels, which permits bats to safely drop into flight from roosts. To improve the effectiveness of alternative roosts, we recommend installation two years prior to project commencement.

To minimize the potential for bat-vehicle fatalities, particularly for bridge roosts over roadways, we alternately recommend the erection of purpose-built structures that are built within the right-of-way.

Integral Roosts

Numerous states have become environmental stewards, actively engineering or retrofitting transportation structures to accommodate bat colonies.  New construction offers an exceptional opportunity to incorporate bat roosts at minimal cost [31]CitationKeeley, B. W., and M. D. Tuttle. 1999. Bats in American bridges. Bat Conservation International, Inc., Austin, Texas. Resource Publication, 40 pp. . At the conceptual design phase, bat specialists can communicate with and advise engineering contractors on appropriate dimensions to accommodate many different species.

To minimize vehicle fatalities, we recommended that ‘integral’ roosts not be incorporated into section(s) that will span traffic lanes. The addition of ancillary, nonfunctional drainage pipes with sealed tops would provide integral roosts with minimal or no vandalism.