Females prefer low elevations, while males are more often found in mountainous areas, particularly from West Texas through Arizona, and northward through at least Oregon. At BCI's workshops in the mountains of southeastern Arizona, we net more than a hundred hoary bats each summer. Fall migration is one of the rare times when hoary bats form groups larger than mother-young family units. At this time, both sexes travel together, often in groups of hundreds, migrating some of the longest distances of any bat. They also overwinter in all the states along the Gulf of Mexico and in northern Mexico.
Hoary bats are the only bats known to hibernate out in the open.
Several have been found on tree trunks, and at least one each has been spotted in a woodpecker hole, a squirrel's nest, and a clump of Spanish moss. It survived a snowstorm and temperatures as low as 7 degrees Fahrenheit. Like red bats, hoary bats wrap up in their extra large, densely furred tail membranes to stay warm, raising heart rates as temperatures fall below 23 degrees. Although no one has seen hoary bats mate, we suspect that, like red bats, they mate in flight, in late summer or early fall, with male and female flying in tandem. The sperm are apparently stored in the female until she ovulates in the spring.