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.
A hummingbird
The smallest birds are hummingbirds. The smallest hummingbird is the Bee Hummingbird.
Hummingbird
The world's smallest bird is the Bee Humingbird.
the humming bird its egg is the size of a jelly bean
The smallest bird is the bee hummingbird, which is 5.7cm long and weighs 1.6g.
Probably a black-legged falconet or hummingbird.
Hummingbird is smaller..
the hummingbird
Hummingbird
hummingbird
hummingbird