September 17, 2019
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Why the hummingbirds in your backyard are so mysterious

Courtesy of Richard Spinney
Courtesy of Richard Spinney
The ruby-throated hummingbird is the only hummingbird to nest east of the Great Plains.

The more I learn about ruby-throated hummingbirds, the less I understand. For instance, there are more than 325 hummingbird species in the New World. A couple dozen visit the western United States, and half of them nest there. But the ruby-throat is the only hummingbird to nest east of the Great Plains, and I don’t know why.

I know that nights in the Rockies can get too cold for them. Unlike western hummingbirds, ruby-throats are not well adapted to freezing temperatures, which occur at elevation even in mid-summer. Ruby-throated hummingbirds have the fewest feathers of any bird, about 940. They get chilly.

For some birds, the Rockies are a barrier to westward expansion. But ruby-throats winter in Central America, along with other hummingbird species, and no mountains prevent them from following their cousins northward from Mexico up the west side of the Rockies. For some reason, they don’t.

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Maybe it’s a food thing. Certainly the vegetation is different out west, but there must be something ruby-throated hummingbirds could eat over there.

Perhaps the other species in the west are more aggressive, keeping the ruby-throats at bay. But I doubt it. As anyone who hosts ruby-throated hummingbirds in the backyard can tell you, our hummers are pretty darned aggressive. The rufous hummingbird is a western species that overlaps its range with the ruby-throat. The rufous has demonstrated its ability to drive off ruby-throats, but I don’t know if all the other species can. Maybe. At 3.5 inches long, our guys are smaller than most hummingbird species. But they’re not as small as the 3-inch calliope hummingbird, which thrives out west. Furthermore, some of the western species get along with other hummingbirds so well that they interbreed.

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Ruby-throated hummingbirds are the most widespread hummingbird species in the world, enjoying a range that extends from Texas to Labrador and everything in between. Perhaps one reason no other hummingbird lives in the east is because none can accomplish the ruby-throat’s migratory route. To reach its wintering grounds in Central America, it flies across the Gulf of Mexico and Caribbean, making the 500-mile jump in a single flight lasting 20 hours. That requires a lot of stored energy, and tiny hummingbirds have little room for storage. It would take 150 individuals to make up one collective pound of hummingbirds.

The long migration is dangerous. Most hummingbirds die the first year. The average lifespan is only about three years. They may look fast, but the bird’s top speed in level flight is only 30 mph. They are nimble enough to avoid most danger in the air, but their feeding habits make them vulnerable to a diverse set of predators, especially if the hunter stakes out a feeder. Greater roadrunners have been spotted doing it. Cats do it. In the tropics, certain snakes hide near attractive flowers. Even a bullfrog or praying mantis is capable of hummer-cide.

Large spider webs snare hummingbirds. I suppose that’s fair. Hummingbirds eat a lot of small spiders. Hummers get their energy from nectar, but their protein comes from a diet of small insects, especially spiders. They are particularly adept at snatching them out of the air from floating strands of web.

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Ruby-throated hummingbirds expose themselves to loads of danger. Although they jump across the Caribbean in one flight, the rest of their migration is leisurely. They fly low in daylight, feeding as they go. When they leave Maine over the next few weeks, they may travel only 20 miles a day, grazing in flower patches all the way to the Gulf of Mexico.

But even that is changing. Over the past quarter-century, some ruby-throated hummingbirds have not bothered to cross the ocean at all. They’ve taken up winter residence in Florida, and even as far north as South Carolina. Climate change.

Since our hummers aren’t in a rush, you needn’t be either. Feeders can stay up through October. Even after your neighborhood ruby-throats have departed, a migrant from the north may pass through and take a sip. More importantly, you might get a rare vagrant from the west. Anything can happen in migration season. Rufous hummingbirds are famous wanderers, and even though they don’t breed in the east, they are regularly seen along the Atlantic seaboard in autumn.

Don’t worry that your feeder will delay migration. The hummers know when it is time to leave, and you can’t talk them out of it. Just be sure to keep your feeder clean, and the food fresh.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.

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