Holloway Wood Duck/Bat House Combo Update

Mark Kiser

Surrounded by a forest and wetlands, Honorary Research Associate Bill Holloway’s property on Toledo Bend Reservoir in western Louisiana is ideal for bats and many other wildlife [TBHR, Fall 1999]. The fact that Wood Ducks (Aix sponsa) share some of the same housing with bats makes his story even more interesting. In February 1999, Bill constructed a pair of combination Wood Duck/bat houses, with duck compartments at the top and roosting chambers for bats below. About 20 free-tailed bats moved in within several months, but when a Wood Duck built her nest in one of the houses in May, the bats suddenly departed. They returned that September, two months after the nestlings fledged. Curious, he left the nesting compartments open for another year to see if the same pattern would emerge.

The next spring, Bill discovered his design was right on target. Hundreds of bats had moved in the previous fall and winter, and when a Wood Duck built her nest in May, the bats did not object. Perhaps initially, bats needed some adjustment time to get used to their “noisy” upstairs neighbors. They have been getting along quite amicably ever since. Wood Ducks nested in both houses in 2001, and hundreds of free-tailed bats continue to use both houses in addition to two ventilated chambers between the pair.

Metric Conversion: 1 inch = 2.54 cm
Figure 2: Front and back are made from 1/2-inch (13 mm) exterior plywood; the sides and roof are made from 3/4-inch (19 mm) exterior plywood. All partitions are 1/4-inch (6 mm) plywood and are dadoed (cut with a router) into the sides. Grooves should be added to one side of all bat roosting and landing surfaces for footholds. Prior to assembly, stain bat roosting surfaces with a dark color, leaving duck compartment interiors untreated. Seal all joints with a paintable latex caulk and assemble houses with exterior-grade screws. Use one coat of primer on house exteriors, followed by two coats of water-based paint or stain. Landing areas are painted black. Place four to five inches (10 to 13 cm) of wood shavings in the bottom of the duck compartments (do not use sawdust, as it retains too much moisture). As an option, adding hinged roofs for each duck compartment facilitates checking and cleaning of nests. To shed rain, slope roofs downwards by adjusting the lengths of the side and front pieces. For more information on Wood Duck boxes, visit the California Waterfowl Association’s Web site at www.calwaterfowl.org/Nestbox.htm or call 916-648-1406. Design by Bill Holloway. Drawing by John Wilcox.

Bill Holloway’s 48 inch-tall (1.2 m) houses are taller than previous duck/bat combo designs. While the top 18 inches (46 cm) resemble a typical duck box, the bottom 30 inches (76 cm) are devoted solely to bats. Each bat section consists of seven roosting chambers spaced 3/4 inches (1.9 cm) apart. Two ventilated, 48 inch-tall (1.2 m) chambers between the houses furnish additional roosting space for bats. Six-inch (15 cm) landing areas provide easy access to all chambers.