Why do birds move that way?

Dear Matt

I was staring out the window the other day at a bunch of birds. Most of the birds were walking around, but a couple of them were hopping. Does this mean something?

-- Bird Watcher, San Diego

Do hoppers look down their beaks at the ordinary walkers as some lower life forms? Don't invite them to parties? Won't let them join the country club? Could be. To big thinkers in birdland, it indicates the evolution of the species and adaptation of birds to various habitats. Hoppers, they say, were principally tree dwellers, since hopping is the most efficient way to navigate from limb to limb. Descendants of ground-feeders generally walk. Some do both; but since they use up more energy hopping, they'll avoid that. As dependent as they are on wing power, hummingbirds can't do either one.