Loss of habitat is to blame, specifically, the lack of the pocket of air between snow and ground called the “subnivean space.” There lemmings winter and give birth to prodigious litters of young.

生存环境的缩小是一个原因，更主要的是它们和地面间被称“空间”里得不到保护，有些旅鼠会冬天生数量惊人却无法存活的小旅鼠。