Two Additional Species Documented to Use Bat Houses

Yuma myotis in British Columbia
When one of Canada’s largest nursery colonies of Yuma myotis (Myotis yumanensis) lost its home last spring, it provided the perfect opportunity to test whether this species would accept bat houses. On March 14, a fire destroyed the historic Squilax church that was the roost of this well-known colony of 2,000 female Yuma myotis (described in Bats of British Columbia).

In April, before the bats’ return to the area, wildlife biologist Dave Low worked with local schools to build bat houses for the returning colony. Six of the houses they made were a wedge-shaped design—about two feet high, with a straight back, forward-sloping roof, and a front that sloped back to a single three-quarter-inch-wide entry space at the bottom. It contained three partitions one-and-one-quarter inch apart, and the fronts and backs were insulated with one-inch sheet Styrofoam. Each house was made from a half sheet of plywood, stained black, and covered with an asphalt shingle roof. A local high school class built an additional 20 single-chambered BCI-designed beginner’s bat houses that they stained light brown. All 26 houses were placed on poles about 14 feet above the ground. Twenty-three of them were erected in forest openings over a four mile strip adjacent to the nearby river and lake. Two single-chambered and one wedge-shaped house were placed in the open space left by the burnt church.

In May, BCI member Chris Harris enlisted the assistance of a local high school to build and erect 19 more houses, using the BCI large nursery house design. He located three pairs on the site of the former church (pictured) and placed the others along the nearby river. All 19 houses were on poles 15 to 18 feet high with all but one being mounted in pairs back to back. Each house was painted either dark brown, light brown, or silver, and oriented in different directions to test the best conditions for Yuma myotis.

By the end of May, only three bats had been attracted to any of the houses. The other returning bats had spread out to previously known Yuma colonies in buildings up to 15 miles away. About 40 percent of the 2,000 church bats, including individuals Chris Harris had previously banded, moved into an old store located a mile southeast, where Yuma myotis were already living.

But starting in late July, small numbers of bats began to appear in all of the BCI large nursery houses. On Aug-ust 10, regional biologists on a bat census discovered 269 Yuma myotis in the wedge-shaped house at the original site. Nine days later, Chris Harris found no bats in this house, while at least 160 bats were jammed into a dark brown pair of nursery houses at the church site. By September 3, all six of the BCI nursery houses at the original church site were filled with bats, including banded individuals from the original church colony. At last check on October 6, four of these houses still contained about 85 bats.

Thus, with a total of 38 houses to choose from, most of the bats had squeezed into the few houses at the original church site. It will be interesting to observe their choices over the next several years. Based on current knowledge, the bats should eventually show a preference for black or dark brown, uninsulated houses with three-quarter to one-inch roosting crevices. The largest houses should be used first, with the smaller ones occupied as the others fill up.

Evening Bats in Florida and Texas
Researcher Laura Finn has identified Ernie Stevens’s nursery colony of 125 bats as consisting primarily of evening bats (Nycticeius humeralis, also known as twilight bats) and a few Mexican free-tails. The colony lives in a shaded bat house in Stevens’s yard in central Florida. Three additional evening bat nursery colonies of about 100 bats each were identified living with Mexican free-tail bachelor colonies in bat houses near Harlingen, Texas. These houses are all exposed to full sun. In each case, the bats seemed to prefer crevices three-quarters to one inch wide. Two-inch-wide crevices were avoided by both species.