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Evaluation of New England Bridges for Bat Roosting Including Methodology and Case Studies

Bats are known and documented to use bridge structures as roosts in various locations throughout the United States and abroad, but there is limited knowledge of how bats use bridges in New England. Significant population declines due to White-Nose Syndrome have resulted in several bat species being listed as state or federally threatened or endangered. If bats are using bridges as roosts, significant effort is required to ensure they are not disturbed or harmed during construction or maintenance work, requiring knowledge of assessment methods to identify likely roost locations in bridges. This thesis describes a two summer study evaluating the bat roosting potential in New England bridges. During this study, 191 bridges were rapidly screened throughout New England for bat roosting potential, with eighteen selected for more detailed evaluations. Various monitoring techniques to determine bat roosting potential were assessed at each bridge evaluated, including acoustic monitoring and analyses, infrared imaging, borescope inspection, visual inspection, emergence studies, and guano testing for species identification. The current federal form required to assess bat roosting in bridges slated for construction work was assessed for its appropriateness in the New England region. A supplemental form has been developed through this study that is recommended to be used in conjunction with the federal form to better assess roosting potential in New England bridges. Training and collaboration is also recommended for personnel completing forms and inspectors familiar with state bridges. When the study began, there was only one known bat bridge roost in New England known. After this two summer study, thirteen bridges have been positively identified as bat roosting sites in New England, with possible roosting at several other bridges. Information gathered through this study on bat roosting potential in bridges and the various monitoring techniques evaluated to positively identify bat roosting in bridges can be used as guidance for state Transportation Agencies developing protocol for construction at potential roosting sites.
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