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.

生存环境是一个原因，更主要是它们在冰雪和地面之间被称为“雪下空间”里得不到护，有些旅鼠会在冬天生下数量惊人却无法存活旅鼠。