One in five of the United Kingdom’s wild land mammals are at risk of extinction within the next decade, The Guardian reports. Researchers from The Mammal Society and Natural England combed through publications and monitoring surveys to produce the first comprehensive estimates of the country’s wild mammal populations since 1995. Whereas some animals like deer and otters have grown in number, others have experienced major declines, largely because of human activity like farming and road collisions. The population of hedgehogs has dropped by two-thirds, for example, and the number of water voles has plummeted from 1 million to just 132,000. Incomplete data mean even these estimates may be optimistic, and the authors say better monitoring of the country’s mammals is urgently needed.