Birds of a feather flock together. Though the phrase is meant to be figurative, if you didn't know better, upon hearing it, you'd think that a bird was equipped with just one kind of feather.
The feathers on a bird's head and belly are much shorter than those on its back and tail. There's actually even more to the differences between these feathers than size.
There are a number of different kinds of feathers, and with different functions. The feathers that are most important in distinguishing one kind of bird from another are contour feathers. These are the body feathers, and together with the flight feathers of the wings and tail, they're what give a bird its shape and coloring.
There are also certain types of feathers that some birds have that others do not.
One good example are feathers called powderdowns. Though these insulating feathers are thinly scattered throughout the plumage of many birds, they are much more abundant and distinct in birds of the Ardeidae family, which includes herons and egrets. On these birds, powderdowns appear in dense patches on the breast and belly.
They're called powderdowns because the tips of the feathers disintegrate into a fine powder, which seems to help waterproof these birds, as well as help them preen, keeping themselves clean of slime and oil from a fishy meal.