大多数鸟在孵卵期间腹部羽毛脱落形成孵卵斑。孵卵斑是由于真皮层加厚，血管增多造成的，有利于腹部热量的传导。不同类群的孵卵斑数目在1-3个不等，而同种鸟的孵卵斑数是一致的，因此可以作为判断亲缘关系的依据。[1][2]
参考资料
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