Some hummingbirds will embark on their fall migration, a move tracked by birdwatchers nationwide who are eager to spot these tiny birds fluttering in their gardens or to their feeders. But ...

Small but speedy. Tiny but aggressive. Little bodies, big appetites. Hummingbirds are a study in extremes. They are the lightest North American birds. Most weigh less than two pennies at 3 to 4 grams.