If the hummingbirds hovering around your nasturtiums seem busier than usual these days, there’s a reason. They are sucking out the nectar to stock up on sugar for energy on their long flight to Central America. They like the sugar water in feeding stations even better.

The little birds double their weight for the long trip. Banding studies show that they fly 20 miles or so a day over land. Then they take 18 to 22 hours for the 500 miles across the Gulf of Mexico, often nonstop, but sometimes they rest briefly on fishing boats or offshore oil rigs.

Hummingbirds come north in the warm months to avoid the competition for food and nesting space in the tropics. But they can’t stand cold weather. They are carnivores, eating as many as 500 insects and spiders a day. They need the nectar and sugar water for energy to go after the bugs. They breathe 250 times a minute and beat their wings as often as 80 times a second. Their wings rotate at the shoulder, permitting alternating forward and backward strokes so they can hover.

They are solitary creatures, migrating alone rather than in flocks or vees like ducks and geese. They are fiercely competitive and often fight each other over feeding grounds.

The fall migration already has begun, so any hummingbirds you see now may be visitors from Canada on their way south. The males, with their ruby throats, go first, so you may see only the less colorful females. The best advice is to keep the feeders loaded with sugar water until a few weeks after you’ve seen the last hummingbird. That way, they will keep coming next year. If they have to look elsewhere for their energy refill, they may skip your place next spring.