To the Bat Cave!

A Creepy Cave

Xiayunling Village， located at Beijng’s Fangshan District， has been the source of many legends about bats. In 2001 summer， zoologist Dr. Ma Jie from the Chinese Academy of Sciences （CAS） went there to search for unknown bat species. After some time， the young doctor found his efforts paying off. From locals， he learned of a huge， dangerous cave that an unbelievably massive population of bats reportedly inhabited.

With this information， CAS’s Institute of Zoology carried out a bat research project in Xiayunling. Brave scientists began periodically visiting to explore the cave for bats. Their bravery is not just talk： Zoologist Dr. Zhang Jinshuo asserted that small-scale collapses happen in the cave all the time. A slight geological accident could trigger a major collapse and bury every scientist in the cave alive.

Recently， a six-member expedition consisting of researchers and animal photographers ventured into the cave. The group’s target was the Rickett’s big-footed bat， a species of vesper bat with large sharp claws and small eyes. The enormous cave features a complex environment and multiple layers. However， no authoritative answer has determined how many layers the cave has. Dr. Lu Jinbo with the Beijing Institute of Geological Survey believes that since caves around Fangshan generally have eight layers， its underground karst caves would as well. Rivers divide lands into smaller terraces， and for the same reason， underground rivers erode limestone to form multi-layered caves. However， the collapsing situation differs from cave to cave.

It is not easy to find bats in such a complicated environment. Expedition members dared not speak loudly because above their heads， long cracks were already visible on many massive rocks， which could collapse instantly without notice. Upon entering the second layer of the cave， fresh bat droppings indicated active bat activity in the area. Greater horseshoe bats inhabited this layer. Considerable numbers of the insect-eaters have been found around Beijing. Compared with other bats， greater horseshoe bats are more resistant to cold and the caves help further： In northern China， the temperature in caves is usually higher than ground temperature in winter.

Seeking Rickett’s Big-footed Bats

The deeper the expedition went， the slipperier the ground became. Collapse accumulations formed the first three layers of the cave and chemical deposits began to appear at the fourth layer. Explorers found scattered calcium carbonate deposits， most of which were covered with moist mud. With various kinds of sediment， this layer resembled karst caves of southern China and ropes were required in order to continue further.

The fourth layer was spacious. But upon entering， vague noises could already be heard. Stone flowers lined the wall， and more stalactites were found. With the noises becoming louder and occasional bats flying overhead， the team realized that a large number of bats waited ahead. When they finally arrived at the fifth layer， the explorers saw countless Rickett’s big-footed bats on the cave roof. They clustered together and squealed like rats when people approached. Hanging upsidedown， the bats gripped the cave roof with their feet and stretched their bodies across rocks. It took a nine-hour trek to witness the only fish-eating bat in Beijing.

Dr. Glover Morrill Allen （1879 –1942） from Harvard was among the first foreigners to closely observe and study Rickett’s big-footed bats. He determined that the rarely-seen creature can catch fish with its feet. Based on Darwinian principles， Dr. Allen believed that every notable organ developed a special function. For this bat， it was its big feet. Although he couldn’t prove big-footed bats eat fish – fish remains were not found in the species’stomachs – the scientist stuck to his theory， with his only evidence being the bats’giant fishhook-like feet. His bold speculation was finally proved correct in 2002. After collecting 15 big-footed bats from the cave， Dr. Ma Jie from CAS discovered fish remains in some of their stomachs， proving at least three fish were consumed by the species.

Most major species of bats living around Beijing such as greater horseshoe bats， Barbastella beijingensis， and even Rickett’s big-footed bats， subsist primarily on insects. Thus， the forest coverage situation in Beijing’s Fangshan District greatly affects them. After conducting surveys at Xiayunling， the expedition learned that in recent years， the population of bats in the area has declined sharply， which leaves forests and rivers around Beijing under threat. This situation is grim enough to inspire humans to worry about the survival of bats， a creature that once enjoyed a relatively stable forest eco-system.