Bats of the genus _Eptesicus_ are cosmopolitan in distribution. A single species occurs in North America, of which Engels (1936) recognizes four races in western United States. [Illustration: FIG. 45. Distribution of the big brown-bat, _Eptesicus fuscus bernardinus_, in Washington.] The big brown-bat appears early in the evening, often before the swallows have retired. This, and its large size, makes it relatively easy to study. It is principally a forest bat but also is found in towns and cities. It is common in Seattle and hunts around street lights and about the trees in the city parks. In its more natural habitat it flies over trees and clearings. Big brown-bats were repeatedly timed, with a car's speedometer, at 17 miles an hour as they flew down a road lined with tall trees. This is a greater speed than that at which they usually hunt. When the speed of the car was increased the bats dodged sideways, around the car. At lesser speeds they pulled ahead and escaped. Big brown-bats are less gregarious, when hunting, than some bats. One or two may be found in a small area, the limits of which are definitely fixed. We noted this repeatedly near Cottage Lake, King County, where the big brown-bats hunted along roads through second-growth conifers. The bats patrolled back and forth along a section of a road about a quarter of a mile in length. When a bat reached the end of its personal territory, it would wheel and return. On six successive trips a bat turned, to retrace its course, at points less than 50 feet distant from the point of the first turn. When the bat approached the turning point on the seventh trip, a bat from the adjoining strip of road approached the area. The two animals fluttered about each other with shrill squeaks, audible 50 feet away. The fluttering and squeaking continued for nearly a minute, after which both bats resumed their hunting. Darkness concluded the observations. On several occasions we stood on a road patrolled by a big brown-bat. The bat immediately detected the watcher and fluttered about his head and face. Big brown-bats ignore other species of bats hunting on their territory. Indeed, such comparatively slow flyers could scarcely drive the more speedy bats away.