translation.en: Two years ago the migrating birds had a multiple event where thousands died because of a mutation occurring in the virus, which made the species range broaden dramatically.
translation.zh: 两年前，候鸟 发生了一场复杂的事件， 由于病毒发生了变异 数千候鸟死亡， 使得所感染的物种范围急剧扩大。