Zoology · Ch 2 — Kingdom Animalia
Class Aves
Class Aves
Aves (Latin avis, bird) are commonly known as birds, and the class's single characteristic feature — found in no other living animal — is the presence of feathers, together with the ability to fly (lost secondarily in a few groups such as the ostrich, kiwi and penguin). The forelimbs are modified into wings, while the hind limbs are adapted for walking, running, swimming or perching depending on the species. The skin is dry and largely devoid of glands, apart from the oil (preen) gland at the base of the tail, used for waterproofing feathers.
The exoskeleton includes epidermal feathers, leg scales, claws, and a horny covering on the beak. The endoskeleton is fully ossified (bony), but the long bones are hollow, containing air cavities — pneumatic bones — which lighten the skeleton for flight. The large flight muscles (pectoralis major and minor) are well developed. Respiration is carried out by compact, spongy lungs connected to air sacs that supplement gas exchange, and the heart is four-chambered, supporting a fully homeothermic (warm-blooded) metabolism. Migration and parental care are both well marked in this class, and the urinary bladder is absent. …
What this figure shows. Eight bird body forms spanning the class's diversity: Vulture, a large soaring bird with broad wings and a bare head; Flamingo, a long-legged, long-necked wading bird with a distinctively down-curved bill; Common Emerald Dove (Tamil Nadu's state bird), a compact bird with iridescent green wing patches; Woodpecker, a bird with a stiff tail and a strong straight bill for drilling into wood; Penguin, a flightless bird with flipper-like wings adapted for swimming rather than flight; Ostrich, a very large flightless bird with long bare legs built for running; Humming Bird, a tiny bird with a long thin bill adapted for hovering flight and nectar feeding; …