Feathers.
When a hummingbird first hatch they are the size of a raisin. The hatchlings have no feathers, their eyes are closed, and their skin is black.
As far as we know, there is no bird living without feathers.
The answer lies in their DNA, but the simplest way to tell that hummingbirds are truly birds is that they have feathers, and the only living creatures with feathers are birds.
No, the biggest difference between birds and other animals is that birds have feathers. Every bird has feathers and everything that has feathers is a bird. A Whistling Swan, in winter has the most with about 20,000 individual feathers. And the fewest feathers? That distinction goes to the Ruby-throated Hummingbird with about 940.
it lays eggs
Yes they are because of people kill them for their feathers and because of habitat loss
Yes, hummingbirds do molt. Until their first molt, the hummingbird has a thin tan or gray color on the outer edge of their feathers. This is most noticeable on the hummingbird's head. Female hummingbirds usually molt after nesting. Hummingbirds usually have one full molt a year.
A hummingbird has four heart chambers, has do all birds.
No, they do not. Somehow a story of a hunter finding a hummingbird in the feathers of a goose he shot started this rumor. This is completely false.
A hummingbird will only lay 1 to 2 tiny, pea sized white eggs. Three babies are too many for the female hummingbird to take care of.
The Ruby-throated hummingbird is the only hummingbird to breed East of the Mississippi River. However, the Rufous hummingbird is a migrant (meaning that it occasionally) ventures out of its territory. So the Rufous has been spotted in Pennsylvania rarely. The Ruby-throated hummingbird is easy to identify. The iridescent feathers on the neck(gorget) of the male Ruby-throated are ruby colored in sunlight.