A hummingbird. Photo courtesy of Julia Bayly

We do not understand much about virtue, as Socrates repeatedly observed. But one thing we know for sure is that size has nothing to do with toughness.

I was thinking about this while a ruby-throated hummingbird probed the flowers on the deck last month, not long before they all made the general vamoose for points south. It dive-bombed me — for fun or fight, I’m not sure — then hovered at the feeder like a fine-tuned helicopter. The ruby-throat’s average size is about three-and-a-half inches. It weighs about one-10th of an ounce. Its wings span barely 4 inches. Its eggs are the size of peas. It eats by poking its beak into blossoms and licking up sweet nectar a drop at a time.

A drop at a time — its tiny grooved tongue flicks 12 times a second. While it hovers, its wings beat 80 times a second. Its heart — an indicator of its metabolism, which is the second-highest among warm-blooded vertebrates (only shrews are more wired) — beats about 600 times a minute, and can double when the bird is really exerting itself. A hummingbird takes about 250 breaths a minute. (Humans take about 12.) It has to eat about every 10 minutes to survive in good health.

These numbers have the sound of precision biodelicacy. Large dragonflies have been known to eat hummingbirds. So have fishing spiders, quick-witted cats and the odd kestrel streaking out of the sky toward the flowers.

But these are unusual catches. In fact hummingbirds have few persistent enemies, and this is due at least in part to their nimbleness — they’re the only birds that can fly backward — and their alertness. They’re fiercely territorial, and mark off careful boundaries in the trees, which they defend like warriors.

But also, they are just physically tough. Hummingbirds can fly up to 50 mph (barn swallows, the reddish-bellied air acrobats, fly about 20 mph), and during spring courtship rituals the males swing and dive in great showy pendulums, beating their wings up to 200 times a second.

Most remarkable, and instructive, is the annual migration.

The ruby-throats are the only hummingbirds that nest east of the Rocky Mountains. They arrive in Maine around the beginning of May (the males get here first, the females a week or two later), and set up camp for the summer. In early fall they start stuffing themselves, partly with the nectar of the remaining wildflowers, partly with insects, and sometimes with tree sap from holes drilled by yellow-bellied sapsuckers.

For what is about to happen is one of nature’s amazing feats of endurance: The tiny hummingbirds, departing Maine at the end of September with stored-up energy, fly not just south, but on across the Gulf of Mexico, covering up to 620 miles nonstop.

The resilient ones make it to the winter homes in Central America. The average ruby-throat may accomplish this feat for four or five years. One durable hummingbird elder lived to be at least 9 years old. Although nearly 10% of other hummingbird species worldwide are threatened with extinction, ruby-throats are not. I don’t know whether to attribute this to good ecological fortune, or to their virtues as a species. One-tenth of an ounce, maneuvering like Blackhawk helicopter pilots around the dangers of the woods all summer and then flying the emptiness of Gulf space to Mexico.

That’s tough.

Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His recent book is “Summer to Fall: Notes and Numina from the Maine Woods,” available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.