Final answer:
Birds have adapted to flight by developing hollow bones with internal support structures, having a single functional ovary in females to reduce weight, and evolving a beak made of keratin instead of teeth and heavy jawbones.
Step-by-step explanation:
Adaptations in Birds for Flight
For birds to shave weight for flight, they have evolved a number of adaptations. First, birds possess hollow bones, also known as pneumatic bones, which significantly lighten their weight without compromising strength due to the internal cross struts known as trabeculae. These adaptations are crucial as they allow for the necessary lift during flight while minimizing energy expenditure.
Secondly, birds have reduced reproductive organs. The females of most species possess only one functional ovary, thus reducing body mass and contributing further to the economy of flight by decreasing the overall weight carried by birds. Lastly, the evolutionary replacement of teeth with a beak made of keratin has also contributed to weight reduction. Keratin, which also composes feathers, scales, and hair, provides the necessary strength for feeding without the extra weight of teeth and jawbones. It's important to note that adaptations like a large body size or thick plumage are not primarily for weight reduction. In fact, a large body size may actually work against flight in terms of weight, as seen in the flightless ostrich, and thick plumage, while not heavily contributing to weight, serves more for insulation rather than weight reduction.