In concise language, briefly talk about why elk are rare animals.

It is native to the marshland in the middle and lower reaches of the Yangtze River in China, and feeds on grass and aquatic plants. I am gregarious, good at swimming, and like to feed on tender grass and aquatic plants. The courtship estrus begins at the end of June and lasts for about 6 weeks. Once widely distributed in East Asia. Later, due to natural climate change and human factors, it was almost extinct in the late Han Dynasty. In the Yuan Dynasty, in order to hunt, the remaining elk were captured and transported to the Royal Hunting Garden for breeding. By the19th century, there was only one group left in Beijing Nanhaizi Royal Hunting Park. Soon after being discovered in the West, it was captured by Eight-Nation Alliance and disappeared from China. Until 1898 was purchased by Britain and propagated to 255, some individuals were sent back to China on 1983. After that, more elk returned to their hometown, and some of them were released into the wild.