As far as we know, there is no bird living without feathers.
All birds lose their feathers,so your answer is that all birds do.
All birds have feathers, and all birds have down, which are the softer, inner feathers.
No. All birds have feathers.
A vulture doesn't and I think a Condor also.
The pigeon is a bird. All birds have feathers, although sometimes the type of feather varies.
Down feathers comprise the fluffy, heat-retaining layer that lies under the water-repellent outer feathers. Down keeps the bird warm. The outer features keep the bird dry. Down ticking, i.e., the feathers stuffed into pillows, mattresses, etc., comes mostly from ducks, especially eider ducks (hence eiderdown.)
yes infact the penguin doesn't have feathers But they do. All birds have feathers of some sort.
Yes. All eagles have feathers on their heads.
All of them.
how the feathers protect the bird
The emu is a bird. Therefore, like all birds, it has feathers. The feathers are wispy, but they are feathers, not fur or hair.