鸟纲是脊椎动物亚门的一纲。体均被羽，恒温，卵生，胚胎外有羊膜。前肢成翼，有时退化。多营飞翔生活。心脏是2心房2心室。仅保留右体动脉弓，左体动脉弓退化。骨多空隙，内充气体。呼吸器官除肺外，有辅助呼吸的气囊。我国的鸟类分为游禽、涉禽、攀禽、陆禽、猛禽、鸣禽六大类。此六类统称为鸟类的六大生态类群。全世界已发现有超过一万种；中国有1400多种。
鸵鸟的排泄行为与其它鸟纲动物有明显的区别。
The excretion behavior of African ostrich was remarkably different from that of other birds.
目的：了解鸟纲蜗管听毛细胞突触的超微结构。
Objective: to understand the ultrastructure of the synapses of the auditory hair cells in avian cochlea.
麻雀，曾为四害，鸟纲雀形目文鸟科麻雀属鸟类的统称，灰头土脸幻想涅槃。
Sparrow, the small wild bird, once denounced one of the Chinese four pests, the general title of the family Passeridae, with ashed apperance dreaming of fantasy nirvana.
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