However, the movement pattern of elephants in this region has not basically changed for over a century, as inferred from descriptions recorded during the 19th century. In the Nilgiri Biosphere Reserve three elephant clans had overall home ranges of , and in the beginning of the 1990s. During three years of survey, their annual home ranges overlapped to a large extent with only minor shifts in the home ranges between years. Conservation The pre-eminent threats to Asian elephants today are habitat loss, degradation, and fragmentation, which are driven by an expanding human population, and lead in turn to increasing conflicts between humans and elephants when elephants eat or trample crops. Loss of significant extents of elephant range and suitable habitat continues; their free movement is impeded by reservoirs, hydroelectric projects and associated canals, irrigation dams, numerous pockets of cultivation and plantations, highways, railway lines, mining and industrial development. Poaching of elephants for ivory is a serious threat in some parts of Asia. Poaching of tuskers impacts on sex ratios that become highly female biased; genetic variation is reduced, and fecundity and recruitment may decline. Poaching has dramatically skewed adult sex ratios in the Periyar Tiger Reserve, where between 1969 and 1989 the adult male:female sex ratio changed from 1:6 to 1:122. Elephant conservation in northern West Bengal has been set back due to high-levels of human–elephant conflict and elephant mortality owing to railway accidents. The railway track between Siliguri and Alipurduar passes through of various forest divisions. Every day, 20 trains run on this track at high speeds. Elephants that pass through from one forest patch to another dash against the trains and die. A total of 39 dead elephants were reported during the period of 1958 to 2008, of which ten were reported killed between 2004 and 2008. In Bangladesh, forested areas that served as prime elephant habitat have undergone drastic reduction, which had a severe impact on the wild elephant population. Habitat loss and fragmentation is attributed to the increasing human population and its need for fuel wood and timber. Illegal timber extraction plays a significant role in deforestation and habitat degradation. As a result of the shrinking habitat, elephants have become more and more prone to coming into direct conflict with humans. In Myanmar, demand for elephant ivory for making tourist items is higher than ever before. The military government shows little interest in reducing the ivory