Assessing Bridge Characteristics for Use and Importance as Roosting Habitats for Bats

Project status

In progress

Start date: 03/01/15
End date: 02/28/18


Principal investigators:

Co-principal investigators:

About the research

The results of this study will be critical to better understanding when bridge replacement/repair/rehabilitation projects have the potential for "taking" (i.e., harassing, injuring, or killing) federally threatened or endangered bat species. This work will lead to efficiencies within the Federal Highway Administration, state departments of transportation, and county engineer offices by informing and ensuring the Fish and Wildlife Service is consulted when necessary. Bats play an important role in the natural balance of many ecosystems. As a result, there has been a growing concern about the number and status of bats in the United States and beyond. Concern over bat populations is primarily driven by the fact that habitats used by bats for roosting and foraging have been disturbed, altered, or reduced. In Iowa, at least one federal endangered bat is known to exist and thought to be potentially impacted by habitat influences. Conservation efforts targeted towards bats can be hampered by a lack of information on their habitats and usage. As a result, many questions may go unanswered as to how to provide suitable environments especially at critical roosting times (e.g., maternal). Fortunately, many bat species are able to adapt to a variety of roosting locations. These roosting locations can include natural "structures" (e.g., caves, trees, rocks, etc.) and man-made structures (e.g., bridges, buildings, etc.). Further complicating the situation is that some locations may be used during brief time durations and sometimes for specific usages (hibernation, maternity, etc.). Although it is widely accepted that bats use bridges as roosting sites, very little attention has given to understanding the characteristics associated with their use as day, night, or maternal roosting sites. Fortunately, unlike periods prior to the 1960s, bridges are recognized as potential roosting locations. This recognition is critical to starting to understand how, why, and when bats use bridges as roosting sites.
The primary objective of this work is to better understand what bridge characteristics (including local topography and habitat availability) are the most likely to be used by bats as roosting locations. The secondary objective of this work is to document the means and methods developed and followed to conduct this work such that the evaluation protocol can be exported to other states/regions. The objectives will be achieved by: (1) establishing the general types of landscape characteristics and "structure" characteristics bats generally prefer; (2) identifying, using geographic information system (GIS) data, bridges in Iowa that are in bat-friendly landscapes; (3) conducting field-surveys of bridges identified using GIS-data to be bat-friendly to identify: (a) evidence of bats using the bridges as roosting locations; (b) structural characteristics of bridges used as roosting sites; (4) analysis of collected information to identify structure/environmental conditions that are most likely to attract roosting bats; (5) reparation of guidance on process and procedures for determining bridge likelihood as a bat roosting habitat in other states/regions; and (6) conducting outreach on applying the research results.



  • Federal Highway Administration Surface Transportation Program (STP) funding
  • Iowa Department of Transportation