Pregnant bats get maternity ward at Fort Casey

People and pets are not the only mammals with camping privileges at Fort Casey Historical State Park. On March 13, 2019, staff installed two handmade bat boxes for the park’s bat maternity colony.

When Fort Casey and area staff launched a Capital project to replace the roof and windows on its historic park office building, they knew there were bats in the attic. The .2-oz, 1.5-inch flying mammals often whipped through the office, creating a health hazard.

Following Washington Department of Archaeology and Historic Preservation and federal standards, contractors installed 11 individually glazed wood-framed windows and slate tiles to match the original roof. The contractor cleaned the attic and added insulation, and park staff added lights and sealed the space. 

But the building had been designated as a bat maternity colony by the Washington Department of Fish and Wildlife (WDFW). So, park construction and maintenance specialists, in consultation with WDFW and private bat experts, set about building maternity boxes for the bats. 

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Pregnant or nursing bats require special habitat: dark, warm, dry and high off the ground. Therefore, staff painted the boxes black inside and out, covered them with the old slate roof tiles and mounted them between two 12-foot timber posts near the building. Little compartments inside give the mamas and babies their privacy. 

At last count, there were approximately 300 mother bats in the attic, and the boxes accommodate that number. Planners opted against adding guano to draw the bats back to the familiar smell, because a deadly fungus called white nose syndrome could not be ruled out in the guano.

The roofing and window replacement cost $160,000. The bat boxes made up a small part of that budget. 

Bats provide natural pest control. They prey on insects, including mosquitoes. The Fort Casey Yuma Myotis bats arrive at the park in spring and leave in October, for parts unknown.