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

Take the ruby-throated hummingbird, for example, which could be hovering by your flowers like a fine-tuned helicopter right now. It’s about 3 1/2 inches long. It weighs about a tenth 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 out 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 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 (hummingbirds are the only birds that can fly backwards) 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 winter homes in Central America. The average ruby-throat may accomplish this feat for four or five years. Some durable hummingbird elders have lived to be 12.

I like our two cats, who skillfully keep mice from infesting the walls and squirrels from chewing up the logs of the house. But despite their 8-pound heft, they’re fat, lazy, mollycoddled Romans with an easy morning’s ride compared to the one-tenth-ounce hummingbirds, who maneuver like Blackhawk helicopter pilots around the dangers of the woods all summer and then fly the emptiness of Gulf space to Mexico. Now, that’s tough.

Dana Wilde, dwilde@bangordailynews.net