1- Body Cover; Their body totally covered with feathers, essential
for thermoregulation, flight, camouflage, and signaling (social and
sexual).
2- Respiration; Air breathing through lung (Birds have one of the
most complex respiratory systems of all animal groups.
- Upon inhalation, 75% of the fresh air bypasses the lungs and flows
directly into a posterior air sac which extends from the lungs and.
connects with air spaces in the bones (pneumonic bones) and fills them
with air.
3- Reproduction; Oviparous (lay hard shelled eggs).
4- Feeding Offsprings, can eat directly after being hatched, no
mammary gland or milk secretion, most of them exhibit parental care
and feeding.
5- Thermoregulation; Homoeothermic, maintains a stable internal
body temperature regardless of external influence.
6- Dentation; Mostly Toothless, and highly modified beaked jaws
according to their feeding habitat
7- Musculoskeletal system; Most of them are tetrapod, with extreme
modifications of the 2 forelimbs into wings.
8- Digestive and urogenital system; Cloaca; a single Exit/entrance
opening where excretion of both urine and fecal matter, copulation
and egg laying occur.