London Bridge Tourist Attraction and Bat Roosting Habitat

Nearly 50 years ago the London Bridge (of nursery rhyme fame), was disassembled and shipped overseas from London to California. It was then trucked to Lake Havasu City, Arizona, where it was reconstructed and rededicated in October 1971. Kay Nicholson, a senior member of Logan Simpson’s team of biological resource specialists, recently completed a bat survey of the bridge in advance of maintenance work to repair and make safety improvements.

The Bridge

The London Bridge is a 5-span structure consisting of a 3-cell reinforced concrete box girder superstructure with cantilevered end spans. The bridge is home to hundreds of bats, which inhabit the nooks and crannies of its hollow interior. The concrete core of the bridge is covered by granite stone facing that was relocated from the original London Bridge in London, England.

The Project

The bearing chamber in the bridge pier closest to the island requires repairs because that chamber is flooded. General contractor T.R. Orr is modifying the bridge to make safety improvements ladders and hand rails in the lower vault chambers associated with the piers) and constructing a wall along the mainland abutment slope beneath the cantilevered end span. A bat survey was required because the bridge is suspected to harbor a large maternity colony during the summer, and the extent of bats roosting during the spring when construction work will occur on parts of the bridge was unknown. Day roosts protect crevice-dwelling bats from predators, weather changes, and provide safety to juvenile bats (pups). Mothers and their pups are vulnerable when their roosts are disturbed or destroyed.

The Survey

Logan Simpson’s Kay Nicholson conducted the bat survey by walking inside the bridge within each outer corridor (i.e., below the southbound lane and the outer northbound lane) of the upper utility gallery for the entire length of the bridge. With assistance from a superintendent with T.R. Orr, she climbed down through access doors into each of the lower vault chambers that slope down toward the piers where maintenance work is planned. Crevices where bats could be roosting were examined with a borescope to determine if any day-roosting bats were present.

The Discovery

Guano (bat feces) was observed on the floor below numerous holes in the walls and ceiling of the upper utility gallery. Using a borescope, it was determined that the holes in the walls were unoccupied. However, a thick, sticky-looking substance surrounding a hole in the ceiling, along with a larger pile of guano below that hole, provided the first clue that the bridge might be occupied by bats. Upon closer inspection, five bats, most likley Yuma myotis (Myotis yumanensis), were roosting in what appeared to be a down drain in the ceiling. With further examination, it was determined that the down drain was plugged above by the lower surface of the bridge roadway. Throughout the survey, the only crevices where bats were observed roosting were these “down drains” in the ceiling. A total of 17 live bats were detected roosting in seven of these ceiling “down drains.” In the lower vault chambers, no bats were found, though staining and guano were present as evidence of bats having roosted there previously.

The Results

The locations where bats were observed roosting was compared to where T.R. Orr will be working in the bridge. Logan Simpson’s Kay Nicholson determined that as long as bat activity does not increase during the course of construction, the maintenance project will not impact roosting bats. T.R. Orr plans to complete construction prior to late spring/early summer, when bat activity is expected to increase and a maternity colony may be present.

Lake Havasu City London Bridge Bats from Logan Simpson Inc. on Vimeo.