Feathers!
Feathers - the only outwardly obvious characteristic unique to birds.
One unique characteristic distinguishing animals from members of other kingdoms is animals have more complex and rapid movements. The movement of sponges isn't more complex.
the endoskeleton
Neptune is extremely windy.
A.) warm bloodB.) hard boneC.) hairD.) liver
Neptune is extremely windy.
Birds have hollow bones. (Except for penguins, which now have solid bones to help them dive)
hair
The single most important characteristic that separates birds from other living creatures is the ability to fly and feathers
All birds have feathers and birds are the only animals that do!
The presence of a cell wall made of peptidoglycan in eubacteria and a lack of peptidoglycan in archaebacteria distinguishes them from members of the other four kingdoms.
absence of a cellular nucleus