By Crystal Chung @crystalkchung
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The incredible images, taken by university researcher Kei Nomiyama, show a colony of eastern bent-winged bats hibernating in a man-made cave.
Also known as Little Japanese Horseshoe Bats, for several years the complete disappearance of the animals during the winter season baffled researchers as environmentalists could not locate their winter hideout.
After much research, this massive colony of around 4,000 bats were found hiding in the mountain on Shikoku Island - the smallest of the four main islands of Japan.
The 36-year-old researcher, who mainly focuses on environmental pollution, said: “When winter comes, eastern bent-winged bats form a colony for hibernation.
"For many years bat researchers were looking for a winter colony, however we realised that they completely disappeared.
“This phenomenon was a complete mystery for researchers. After many years we finally found this valuable colony. This was huge delight for us."
During the winter months when temperatures drop to just above freezing, the bats go into hibernation in caves.
Kei, who lives in the city of Matsuyama on Shikoku island, said: “The artificial bat cave exists up in a mountain in Shikoku island.
"In order for me to reach the cave, I have to drive for about three hours by car from my hometown."
The photos show the tiny little animals grouped together and flying through artificial cave where they have set up home for the winter.
Although the exact location of the cave is unknown, as researchers cannot give away the precise location, it is understood it is actually a channel used to access a mountain.
The eastern bent-winged bat gets its name from its unique anatomy - on the third 'finger' of its wing, the last bone is four times longer than the middle one, giving a bent appearance.
Researchers state that there are thought to be just under 41,000 of the bats left, after a population decline of 67 per cent since the 1990s.
Kei said: “The number of these bats decreases every year in Japan. This may be due to the influence by environmental destruction."