1.
birds, rabbits
A counter for birds and rabbits. Historically, rabbits were counted with this counter because monks could eat rabbit meat if they called them 'birds.'
羽 is specifically for birds and rabbits. Pronunciation varies: 一羽, 二羽, 三羽, 六羽, 八羽, 十羽. The origin of counting rabbits with this counter is said to come from Buddhist monks who wanted to eat meat; by calling rabbits 'birds,' they could justify eating them.