アブラコウモリ（Japanese Common Pipistrelle) Pipistrellus abramus
In Japan 日本
Japanese Common Pipistrelles can be found from the southern region of Hokkaido to Okinawa prefecture. They are the most common bats in non-mountainous areas of Honshu, Sikoku and Kyushu. They roost almost exclusively in man-made structures. They roost in attics, under the roof tiles and shutter pockets of houses. They also roost under the parapet wall caps of buildings and narrow spaces between concrete blocks of raised roads and railroads. We can't even imagine where they used to roost before human population had increased to the point we have today. This situation is similar to the barn swallow.
Japanese common pipistrelles are often seen flying in large numbers over water surfaces or near water. This is because the small insects they prey on swarm over such bodies of water. The bats sometimes skim over and drink the water in the evening after a hot day. Once, we captured a Japanese Common Pipistrelle flying straight out of a roost with a mist net and put an identification band on its arm. Then, we happened to recapture the exact same bat about one hour later returning from feeding session. We found that the bat of 6g gained an additional 1g.
Japanese Common Pipistrelles emit ultrasound calls from their mouths and listen to the echoes bouncing back from obstacles and prey(echolocation). In their search phase, Japanese Common Pipistrelles emit short pulses with 5ms durations 10 times per second. One pulse consists of a frequency modulated(FM) component which is a short, steep sweep dip in the frequency from 80kHz to 40kHz and a quasi-constant frequency component(QCF) which is a short, relatively constant frequency at the end of the call. The peak frequency of the call is about 45kHz.
When bats hunt at night they are also exposed to the danger of being hunted by nocternal predators. Japanese Common Pipistrelle’s remains are often found in the pellets of brown hawk owls. Sometimes they emerge in early evening or late afternoon while it is still light and are hunted by Northern Goshawks and Common Kestrels. Recently, these birds of prey have become urbanized and built nests in buildings. So, Japanese Common Pipistrelles which are abundant in urban areas are one of their best targets.
Baby bats of Japanese Common Pipistrelle are born in late June or July. Most bats give birth to only one pup at a time, but Japanese Common Pipistrelles are hightly fertile compared to other species, and bear two or three pups. The pups are born blind and naked. Eight or nine days after the birth, their eyes open. Within two weeks of the birth, the pups are fully furred. The pups make their first flight in early August. They become as large as adults in late August but still weigh less than adults. Juvenile Japanese Common Pipistrelles' fur is darker in color than adults' fur.
Japanese Common Pipistrelles fly out at around sunset to forage. Lactating females go back to their roost in one hour to feed babies but non-lactating bats don't always go back to the roost during the night. Instead, they often use a night roost in places such as a building wall near the feeding site. They are often seen resting at night roosts in groups in late August as in this picture.
The lifespan of Japanese Common Pipistrelle has not been investigated enough, but the longest life recorded of a female bat is 5 years old and, for a male bat is 3 years old, which are very short lifespans for a bat. It has been reported that most male bats die within 10 months.
Japanese Common Pipistrelles stop flying out on cold nights in late November, and go into hibernation. Mating occurs in October, which is just before hibernation. On some warm days in winter they rouse and fly out. Our D500X Bat Detector has captured Japanese Common Pipistrelle calls in January. If the weather becomes warm in March, the bats go out to feed at night.
In Taiwan 台湾