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April 2001
Any moment now, the ruby-throated hummingbirds will be returning from their winter habitat in Central America. How will we entertain our guests, who come to mate, nest, and raise their young to continue their species?
Here near the northern edge of their range, their arrival in early May precedes the blooming of their nectar food sources. They instead drink tree sap oozing from the holes made by yellow-bellied sapsuckers and feed on small insects attracted to the sap.
Males and females associate only during mating and do not form a pair bond. Each male mates with several females. Each female makes her nest and raises her young by herself and protects a territory around her nest. She either builds a new nest or reuses an old one. The nest is located on a small tree limb, often covered with lichen and usually ten to twenty feet above the ground. It is protected by foliage above, and is often over or near water. Made of bud scales, lichens, and plant down, the nest is held together with spider silk. The outside diameter of the nest is only one to two inches, about the size of half a walnut shell.
The female lays two white eggs, each about the size of a pea. She incubates the eggs for about two weeks. The nestlings are in the nest for two to four weeks. Once the young fledge, they stay around the nest for up to month. The female often takes fledglings to nectar food sources. A female may mate again and have a second brood, but in Maine's cooler temperatures, nestlings may grow more slowly and females may not have time for a second brood.
Males aggressively protect a territory of about one quarter acre that contains nectar food sources and a perch or two. They chase out other ruby-throats and sometimes larger insects such as bumblebees and sphinx moths. As the season progresses, and other flowers bloom, the territory may shift.
Ruby-throats weigh less than a penny, about one tenth of an ounce. Their hearts beat more than six hundred times a minute. They must feed almost constantly during the day, every ten minutes. They feed at nectar sources, not by sucking, but by licking three times each second. Small insects and spiders on the flowers round out their diet. They perch frequently, to groom their feathers, rest and oversee their territory. At night, their body temperature drops, their metabolic rate slows, and they enter a state of torpor. They would starve overnight without this adaptation.
A small damp area, very shallow water, perhaps an eighth of an inch deep, or a hose mist will provide water for drinking and bathing, which they do at least once a day. In the very early and very late periods of the season when blooming flowers are scarce, nectar feeders are a great help, but only if kept scrupulously clean. Shrubbery and trees near the flowers provide the necessary perches between feeding bouts.
Our gardening efforts assist hummingbirds' survival. Their nectar food plants are tubular, odorless, nodding down and brightly coloured. Look carefully at plants when you are selecting them. While some flower clusters are upright, the individual flowers within the cluster may be nodding, such as penstemon. While ruby-throats seem to prefer red, orange and yellow flowers, they will also use white, blue, pink and purple ones. Annuals, biennials and perennials, as well as some shrubs and vines, with staggered blooming times will provide a continuous source of nectar food. Always select single blossoms instead of double ones so that the nectar is accessible. Large clumps and drifts of flowers are very attractive.
Unique to the Western Hemisphere, there are about three hundred and twenty species of hummingbirds. Most live their entire lives in South America, Central America, and the Caribbean. About sixteen species come into North America regularly to breed. The ruby-throat is the only hummingbird that breeds east of the Mississippi River.
By Nancy Coverstone (ncstone@umext.maine.edu), University of Maine Extension Educator in Androscoggin and Sagadahoc Counties
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