The little brown bat is one of the most numerous bat species in many locations, including Oregon. With a body that rather resembles a mouse, and relatively long wings compared to its body size, it is also a voracious and talented hunter. For many people, few sights are more amazing than to see little brown bats feeding in the forest, especially near a lake or river, at dusk.
This little 'mouse with wings' seems to flutter without effort, in open areas, between tree limbs and other obstacles, never quite hitting them. They will skim low over the surface of water and abruptly fly high up into the air, pivot, and work back the way they came. Watching them zip around, missing things in their paths, including other bats; it becomes easy to forget that there is a definite reason for their movements. It is an important reason, too: feeding.
A little brown bat can eat over its own body weight in insects every night. It has such a high metabolism that this is necessary in order for the bat to survive. They would otherwise starve to death. This is a considerable accomplishment, too, considering the relative size of a flying insect such as a mosquito, and the size and weight of the bat, as small as it may be. The feeding behavior is one of the keys that make it possible for these little bats to eat so many insects in the short time between daylight and darkness.
Like many bats, the little brown bat hunts by using echolocation. It emits high-pitched squeaks and if these encounter an object, some of that sound is bounced back to them. From this information, they can determine the size of the object, whether it is moving or stationary, where it is located, and if it is moving, how fast it is moving.
With its tremendous aerial agility, this allows the bat to catch its prey and to avoid colliding with objects or even other moving bats.
Considering this, lets break down the previously observed feeding behavior. Detecting stationary objects, the bat misses tree branches and other stationary in its flight path. It then skims low across the surface of the water, where a great number of flying insects will be located. As it catches one, it eats it on the wing and is almost immediately ready for the next.
Detecting insects above, it angles up and through those insects, again eating as it goes. Then it turns back, drops altitude, and again skims across the surface, continuing to eat. Thus, it often completes a lazy figure eight pattern. This maneuver can be done repeatedly.
Though little brown bats can be found from low altitudes to high altitudes, they are also not strangers to towns or cities, though these present new problems and opportunities. For instance, though there are more obstacles, streetlights draw insects, making it easier for the bats to find and devour prey. Attics and crawlspaces also give the bats a convenient place to roost when they aren't hunting, and to hibernate when the weather gets cold.
Further, little brown bats are one of the first predators to adjust to eating non-native introduced flying insects. An example is a small green insect imported from Japan to the Klamath Falls area of Oregon, in the 70s. The idea was that these 'rice bugs', as they are locally known, as larvae, eat mosquito larvae, and the area had problems with mosquitoes. What wasn't considered, however, is that the rice bugs didn't have any natural predators. Populations of the little green midges exploded.
Enter the little brown bat. Deprived of the large quantity of mosquitoes they would normally have eaten, the bats gradually began to eat the midges.
Sadly, because of the bias of many people, little brown bats were killed quite often, when they were found in attics and the like. The people never realized the great good the little bat was doing. Thankfully, this attitude is slowly changing and the little brown bat population is recovering in the area. With this change, the number of rice bugs taken is on the increase. It will still take time for the bat population to get great enough to make a significant impact on the midges the bats are now feeding upon. These bats may look like winged mice, but they don't multiply anywhere near as quickly.
The feeding behavior of these bats is interesting to watch, whether a person is in town or out camping, and understanding how and why they feed as they do, unlocks some of the curious behavior exhibited. It is worthwhile to watch little brown bats feeding when possible, and to be thankful they are on our side.