A hummingbird huddles on my fence in the rain scowling resentfully. I'm probably anthropomorphizing but he sure looks miserable. He's in no actual danger. Animals have evolved various adaptations to deal with the cold. Frogs and turtles move to the bottom of the lake, hibernating down where cold water holds more oxygen. There's a snow fly that self-amputates its frozen limbs and grows new ones. Unlike my little visiting friend, many birds migrate when days grow short and the weather cools. But this Anna's Hummingbird (Calypte anna) has developed a unique way to survive the winter.
Anna's Hummingbird is the only hummingbird seen regularly during winter in California. Instead of migrating, it may move short distances to find better feeding grounds or a well-supplied feeder. Anna's Hummingbirds overwinter in our area, entering a state of torpor when temperatures drop. In hummingbirds, torpor lasts overnight in contrast to hibernation which is more prolonged.
When this hummingbird enters torpor, its metabolic, heart, and respiratory rates drop. Its normal body temperature is 107 degrees Fahrenheit; during torpor, that can drop to 48 degrees. The heart beats about 1,220 per minute when flying but drops to 50 beats per minute during torpor. Once the sun comes up, hummingbirds quickly return to full activity.
Anna's are the largest hummingbirds on the West Coast. They are found from Baja California north to Vancouver B.C. They are mostly green and gray with a white dot on the outside corner of the eyes. As a testament to the beauty of their iridescent feathers, a flock of hummingbirds may be called a bouquet, a glittering, or a shimmer. The reddish-pink throat and cap of my fence visitor identify him as a male.
When courting, a male will catch the female's eye by flitting back and forth in front of her, then climbing as high as 130 feet in the air. He then completes a courtship dive, plummeting at speeds up to 60 mph and stopping on a dime in front of the object of his admiration.
Anna's Hummingbirds eat nectar from various flowering plants, most likely manzanita this time of year. They also eat small insects and tree sap. They feed through a long, tube-like tongue that absorbs nectar much like a paper towel absorbs water. Due to the ability to rotate their wings in a circle, they can fly forward, backward, up, down, or flutter in place. Hummingbirds can even fly upside down to evade predators.
Anna's Hummingbird was named for an Italian duchess, Anna de Belle Massena. As Mistress of the Robes to Empress Eugénie, wife of Napoleon III, she impressed the French naturalist, Rene Lesson with her beauty. He named the bird after her though ironically, hummingbirds were only found in North America and it is unlikely she ever saw one.
コメント