“Perhaps more so than for any other wildlife issue, the potential effect on bats is independent of the scale of the operation concerned. Very small structures can be important to large populations of bats or to species of critical conservation importance. All highway projects should take account of the potential presence of bats.“
“Although the preservation of traditional commuting routes is important, “bats continue to seek new connections in a changing landscape. We must therefore not just aim at maintaining existing and highly important routes but also at a general ‘permeability’ of the landscape.”
“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.”
“Bat species can differ as much from one another as a swallow does from a mallard.”
Forty-seven microchiropteran species of 20 genera and three families populate the United States. Of those species, 61.7 percent (29) and potentially 87.2 percent (41) exploit manmade transportation infrastructure (i.e., > 6 m bridges, box culverts, drainage structures).
Artibeus jamaicensis, Jamaican fruit-eating bat
Choeronycteris mexicana, Mexican long-tongued bat
Corynorhinus rafinesquii, Rafinesque’s big-eared bat
Corynorhinus townsendii, Townsend’s big-eared bat
Eptesicus fuscus, big brown bat ‡
Lasionycteris noctivagans, silver-haired bat
Lasiurus cinereus, hoary bat
Leptonycteris yerbabuenae, lesser long-nosed bat
Macrotus californicus, California leaf-nosed bat
Myotis austroriparius, southeastern myotis ‡
Myotis californicus, California myotis
Myotis ciliolabrum, western small-footed myotis
Myotis evotis, long-eared myotis
Myotis grisescens, gray myotis ‡
Myotis leibii, eastern small-footed myotis ‡
Myotis lucifugus, little brown myotis ‡
Myotis occultus, Arizona myotis
Myotis septentrionalis, northern myotis ‡
Myotis sodalis, Indiana myotis ‡
Myotis thysanodes, fringed myotis
Myotis velifer, cave myotis ‡
Myotis volans, long-legged myotis ‡
Myotis yumanensis, Yuma myotis ‡
Nycticeius humeralis, evening bat
Nyctinomops macrotis, big free-tailed bat
Parastrellus hesperus; canyon bat, western pipistrelle
Perimyotis subflavus, tri-colored bat ‡
Tadarida brasiliensis, Mexican free-tailed bat
‡ denotes species susceptible to white-nose syndrome
Eumops floridanus, Florida bonneted bat
Eumops perotis, greater bonneted bat
Eumops underwoodii, Underwood’s bonneted bat
Idionycteris phyllotis, Allen’s big-eared bat
Leptonycteris nivalis, Mexican long-nosed bat
Molossus molossus, Pallas’ mastiff bat
Mormoops megalophylla, Peter’s ghost-faced bat
Myotis auriculus, southwestern myotis
Myotis keenii, Keen’s myotis
Myotis melanorhinus, dark-nosed small-footed myotis
Nyctinomops femorosaccus, pocketed free-tailed bat
Globally, bats are intrinsic to healthy ecosystems, community integrity and vital ecological processes. They provide valuable ecosystem services, products and provisions, cultural benefits and contribute considerably to mammalian diversity. Notwithstanding, bats confront multiple threats; habitat destruction and modification, climate change, pesticides and pollution, disease and human development 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.
Our objective was to produce comprehensive but practicable guidelines to harmonize transportation requirements with environmentally sustainable management practices – a framework by which transportation authorities can orchestrate bat mitigation, management and conservation initiatives.
Transportation authorities 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.
There are no rules Bats exhibit inter- and intraspecific plasticity (e.g., roost selection and seasonal activity) and no overarching “rules” exist to determine probability or pattern of use. “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.” Bat Conservation Trust 2007
Timing is key Biological milestones (e.g., maternity season, hibernation) may vary geographically and by species; optimal timings must develop from practical experience and familiarity with endemic species.
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.
The publication ‘Bats in American Bridges,’ by Keeley and Tuttle, 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.
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