What important and unusual physical property (for birds) do ostriches and penguins share?
bonelessness
waterproofness
webbed feet
flightlessness
There are about 10,000 living species of birds. Almost all of them can fly. Flying birds are classified in 29 orders. Most species belong to the order of perching birds. A few birds are flightless, such as the ostrich and penguin, but they evolved from a flying ancestor.