Species profile: Ruby-throated Hummingbird
Published: May 1, 2000
|There he was, resplendent in his metallic green body and dazzling red throat, hovering at the window in the exact spot where the sugar-water feeder had hung the previous summer. Much to my surprise, the male Ruby-throated Hummingbird we had dubbed "Guard Bird" (often shortened to GB) was already back in Wisconsin from his winter retreat in the Tropics. |
Since we had observed only one male ruby-throat at the feeder the previous year, and because many hummingbirds exhibit site loyalty, we felt confident that this was in fact Guard Bird. "Where's the food?" he seemed to be wondering. Admittedly, it was May 6, and I had been a little slow in putting out our hummingbird feeders. I quickly filled the feeder and hung it in its usual place; within minutes, GB was busily sipping sugar water.
Guard Bird had been the dominant male at both the flowers and the feeders in my bird garden. He maintained his autocratic control over the food and habitat by chasing all other hummingbirds away - all except "his" females. In what amounts to an avian form of prostitution, male hummingbirds exchange food for sex from the females. Competing males are promptly escorted out of the area on a fast track that would make any bird's head spin.
Male Ruby-throated Hummingbirds advertise their dominance with dramatic aerial displays of sweeping pendulum flights, 40 to 50 feet above the garden. These displays not only warn off other males; they also impress females in the area. Proof of GB's success in that department appeared last July when the feeders in our yard were suddenly repopulated with short-tailed green hummingbirds with white bellies - presumably GB's offspring.
Like other male ruby-throats, GB played no part in the rearing of last year's young. Female ruby-throats
select the nest sites and craft tiny cups of plant down, fibers, and bud scales, which are attached with spider silk to tree limbs. Each nest, placed about 10 to 20 feet above the ground, looks so much like a knot on the branch that you can look at one and easily miss it.
After five to ten days of nest building, the female lays the first of two pure- white eggs, which are the size of navy beans. She incubates the eggs for 14 to 16 days until they hatch. For the next three weeks, she feeds the youngsters by regurgitating nectar and tiny insects into their throats with her swordlike bill, a somewhat unnerving sight to behold.
Throughout the southeastern states, two broods per season are common. Ruby-throats in the northern part of the species' range also sometimes raise a second brood.
Short periods of cold weather are not a big problem for adult hummingbirds. They endure low temperatures by placing themselves into a state of torpidity to save energy. Torpidity slows down their respiratory and metabolic systems, making the diminutive birds appear to be asleep or dead. People who find "sick" hummingbirds hanging from sugar-water feeders may not realize that the birds are most likely awaiting warmer weather and better feeding conditions.
When fully powered-up, hummingbirds are the most amazing of all flyers. They are the only birds that can fly
forward, backward, and up and down. These amazing aerialists can also hover at dead still or fly straight at speeds of up to 75 miles per hour. If you hang a sugar-water feeder just outside a window, you can see how a hummingbird's wings rotate to accommodate any direction of flight.
Perhaps the most astounding feature of these remarkable little birds is their annual migration to and from the
Tropics. The male ruby-throats leave first, followed by the females and later by juveniles. It is truly amazing how a young hummingbird, hatched just a few weeks earlier and weighing no more than one-tenth of an ounce, knows when to fly south, where to go, and how to get there.
In fact, a great many Ruby-throated Hummingbirds do not make it to their wintering grounds in the Gulf Coast, Mexico, and Central America. Many perish en route, particularly those that cross the 600-mile stretch of water in the Gulf of Mexico. Night fishermen in the Gulf tell stories of exhausted and disoriented birds of all kinds that land on their boats; the many exhausted birds that don't find a boat on which to rest presumably die.
Those hummingbirds that survive the journey south and the winter that follows return in spring, hungry after a long and physically demanding trip. And some, like GB, appear on patios like mine throughout the country
expecting to find feeders filled with sugar water awaiting their arrival.
Did You Know?
• The ruby-throated is just one of 16 species of hummingbirds that breed in the United States and Canada, but the only one regularly found east of the Rockies. The other species frequent the West Coast, the High Rockies, and the Southwest. All can be attracted to sugar-water feeders and to gardens containing nectar-producing flowers (see "Gardening for Birds" on page 76 of the June 2000 issue).
• The heart of an adult male Ruby-throated Hummingbird beats about 200 to 600 times per minute, but the heartbeat can accelerate to about 1200 beats per minute if the bird is feeding or agitated.
• Hummingbirds eat small insects in addition to nectar. Some studies indicate that insects may comprise up to 60 percent of a Ruby-throated Hummingbird's diet.
|George H. Harrison writes from his home in Hubertus, Wisconsin.||