By BILL CHAISSON
By Bill Chaisson
Even before I traveled to Mexico and the western United States and encountered a portion of the multitude, I thought it was a shame that we had only one hummingbird species in the eastern U.S. This is a frequent occurrence in the biogeography of songbirds and small mammals or, in short, anything that has difficulty dispersing over high mountain ranges.
For example, there is one eastern towhee, but there are three western species, the Abert’s, the canyon, and the California towhee, as well as the spotted towhee, only recently distinguished from the eastern. Another example: there is only one quail in the eastern U.S., the bobwhite. There are five out west: the California, the Montezuma, the scaled, the mountain, and Gambel’s. Among mammals, the clearest example is the chipmunk. Here in the east, we have one species (currently ubiquitous), while out west there are 22.
The ruby-throated hummingbird is found throughout the eastern half of the continent, north to the southern edge of the great coniferous forest that stretches across Canada. In Canada it ranges west to the Rockies, but in the United States it doesn’t get much beyond the Mississippi Valley. The ruby-throat’s weight can be measured in grams, but it manages to migrate to the Caribbean and Mexico each fall in search of plants that flower during the winter months and temperatures that won’t turn it into an avian ice cube.
Like several of our migratory bird taxa, the origin of the hummingbird family, Trochilidae, and the apex of its diversity is in the Neotropics. During the interglacial intervals of the Pleistocene, these tropical families have diversified by expanding northward into the subtropical and temperate latitudes that were repeatedly disrupted during glacial intervals. Several times over the past 2 million years, the climate of the southern United States has more closely resembled the present climate of southern Canada. Each time the disrupted ecosystems recover during the ensuing warm period, it represents an opportunity for new bird species to develop in newly (re)opened territory, a phenomenon known as allopatry.
A 2007 paper in the journal “Systematic Biology,” Jimmy McGuire of UC Berkeley and three colleagues used statistical analysis of several DNA sequences to classify about half of the 334 extant species. They concluded that most hummingbird groups originated in the lowlands of South America and spread north into Central America and Mexico, but only reached North America relatively recently. In a 2014 paper McGuire and others added the dimension of time, estimating that the ancestral hummers had colonized South America from the Old World 22 million years ago. They found that the northward spread of the group was affected by the emergence of the Panama land bridge (between 3 and 5 million years ago). The ruby-throated hummingbird is part of the “bee” group (one of eight in the family) which, unlike most of the other clades, is thought to have originated in Central America.
The ruby-throat (Archilochus colubris) shares a genus with the black-chinned hummingbird (A. alexandri) of northern Mexico and the American Southwest. Both are tiny animals between 3 and 3.5 inches long and weighing perhaps 5 grams (2/10 of an ounce). The male birds have “gorgets,” bibs of glossy feathers that cover the throat and upper breast. The ruby-throat is named for its gorget; the black-chinned’s is a dark metallic purple.
I put out a hummingbird feeder in late spring and was soon unsatisfied with it. It had no perches, and I didn’t think the design allowed the wells to fill with enough nectar. So, I bought a two-tiered model with bright yellow plastic flowers around the nectar wells and visitation immediately improved.
Hummingbirds favor red or orange flowers, but you will see them hovering at tubular blooms of all colors, including trumpet creeper, cardinal flower, honeysuckle, jewelweed, bee-balm, red buckeye and red morning glory. Sugar concentration in the nectar is the paramount criterion. They also pick insects out of the air like a flycatcher or pluck them from spider webs (they will also eat the spiders). Young birds in the nest are fed nectar and insects, as nectar does not offer sufficient protein to sustain rapid growth.
A couple of weeks ago I remarked in a column called “When birds become retiring” that I was waiting for more hummingbirds to come to my feeder. Because they are fiercely territorial and solitary, I was hoping that the female, who raises the young on her own, would bring her fledged brood to the feeder. That has not materialized and we continue to see mostly the male, who may or may not let any others feed at his station.
Hummingbirds are polygamous and do not form pairs; both males and females may have multiple mates. The males arrive first in the spring and court females that enter their territory. The females then build a nest made of leaf bud scales held together with spider web and lined on the outside with lichens. The walnut-sized nests are placed on top of a branch that is descending at a low angle, usually in a deciduous tree. They may be repaired and used year after year.
According to the “Atlas of Breeding Birds in New Hampshire,” ruby-throated hummingbirds are found throughout New Hampshire, but are not common. They arrive in May and begin to depart in mid-August. Even in New Hampshire, the females may raise two broods in a season, building a second nest before the initial brood is out of the first. Many northeastern birds head for the Gulf Coast, where they pause to double their fat content in order to make the 800-mile flight across the Gulf of Mexico to the Yucatan.
Bill Chaisson, who has been a birdwatcher since age 11, is a former editor of the Eagle Times. He now works for the Town of Wilmot and lives in Sutton.
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