A major challenge to Darwinian evolution is explaining 'rudimentary' organs. This is particularly relevant to birds: rudimentary wings occur in fossils, as well as in developing, molting, and flight-impaired birds. Evidence shows that young birds flap small wings to improve locomotion and transition to flight. Although small wings also occur in adults, their potential role in locomotion is rarely considered. Here we describe the prevalence of rudimentary wings in extant birds, and how wings wax and wane on many timescales. This waxing and waning is integral to the avian clade and offers a rich arena for exploring links between form, function, performance, behavior, ecology, and evolution. Although our understanding is nascent, birds clearly show that rudimentary structures can enhance performance and survival.

达尔文进化的主要挑战是解释“基本”器官。这与鸟类特别相关：原始的翅膀出现在化石中，以及发育，蜕变和飞行受损的鸟类中。有证据表明，幼鸟拍打小翅膀可以改善运动并过渡到飞行。尽管成年人也有小翅膀，但很少考虑它们在运动中的潜在作用。在这里，我们描述了现存鸟类中基本机翼的流行情况，以及机翼在许多时间尺度上如何起蜡和消逝。这种蜡化和减弱是鸟类进化枝不可或缺的组成部分，为探索形态，功能，性能，行为，生态和进化之间的联系提供了一个广阔的舞台。尽管我们的理解是新生的，但鸟类清楚地表明，基本结构可以提高性能和存活率。