Discover the clever optical trick that gives hummingbirds their characteristic iridescence, among other hummingbird facts.
Discover hummingbird facts and beautiful life-size pictures of hummingbirds in the aptly-titled Hummingbirds (Harper Design, 2014) by Michael Fogden, Marianne Taylor and Sheri L. Williamson. Boasting detailed species profiles that include information about behavior, plumage and habitat, as well as population statistics and flight maps, Hummingbirds is stuffed with enough hummingbird facts to satisfy even the most avid birder. The following excerpt is from the Introduction.
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Hummingbirds are tiny, captivating, vibrant, and pugnacious. They include the smallest birds in the world and many that are sublimely beautiful, with glittering, iridescent plumage ornamented with showy tufts and plumes. They have unique flying skills and a rare ability to enter a state of torpor. The smallest species have the highest metabolic rate of any warm-blooded animal and spend much of their life on a knife edge, often within hours of death by starvation. If they were any smaller, they would be unable to produce energy quickly enough to survive. Hummingbirds have extraordinary appeal, and their extravagant names, full of allusions to jewels, fairies, and sunshine, give an idea of the way in which they have captured the imagination. Fiery Topaz, Crowned Woodnymph, Empress Brilliant, Shining Sunbeam, and Long-tailed Sylph are good examples, as is the ancient Aztec name huitzitzil (rays of the sun). The Mexican chuparosa (rose-sucker) and Brazilian beija flor (flower-kisser) are picturesque descriptions of the birds’ feeding behavior, while the Cuban zum-zum is an apt description of how they sound in flight.
The beauty of hummingbirds appealed to artists, authors, and poets in the Western world, as expressed in Emily Dickinson’s poem “Within my Garden, rides a Bird.”
This fascination proved deadly for the birds, however, as it became fashionable in the mid-nineteenth century to use their feathered skins to decorate women’s hats. In South America, millions of hummingbirds were slaughtered and then exported to Europe. Many specimens found their way into museums, including some species described in this book that have never been seen since.
Today, hummingbirds continue to captivate us, but luckily for the species they now attract tourists rather than trappers. The growth in hummingbird tourism has escalated thanks to the rapid proliferation of hummingbird feeders in locations all over North, Central, and South America. It has never been easier to see rare or spectacular hummingbirds at close quarters than it is today — go to the right feeders in the right country, and it is even possible to see such iconic species as the Crimson Topaz, Gorgeted Sunangel, Wire-crested Thorntail, Marvelous Spatuletail, Sword-billed Hummingbird, Booted Racket-tail, and Velvet-purple Coronet.
According to the most recent taxonomic classifications, hummingbirds currently include 338 species in 105 genera. The majority are distributed through the New World tropics, with diminishing numbers to both the north and south. The Rufous Hummingbird breeds as far north as Alaska and the Green-backed Firecrown as far south as Tierra del Fuego. Few families of birds have representatives in such extreme environments, ranging from steamy equatorial rainforests to hot, dry deserts and freezing mountain peaks.
Unlike such attractive birds as American warblers, tanagers, and orioles, whose brilliant colors appear the same whatever the position of the viewer, the iridescent colors of hummingbirds change with the angle at which they are observed. Colors are often fleeting, and even appear black in poor light. Non-iridescent colors are produced by chemical pigments in the barbules of the feathers, which absorb some wavelengths of white light and reflect the rest, which the eye sees as the complementary color. On the other hand, the iridescent colors of hummingbirds are structural rather than chemical in nature, and are caused by interference.
Interference can perhaps be understood by considering the rainbow colors seen on a thin film of gasoline on a puddle of water. Light is reflected by both the water and the gasoline surfaces but, because of the distance it travels through the thin film of gasoline, light of a particular wavelength reflected by the water is out of phase with light of the same wavelength reflected by the gasoline. The out-of-phase wavelength interfere with one another and cancel each other out, the result being that the remaining wavelengths no longer combine to make white light and are seen as a color. The surface of the gasoline film appears rainbow colored because the distance light travels through the film, and hence the color that is produced, varies with the viewing angle. Since the wavelengths of light are very short, interference occurs only with very thin films. In hummingbirds, suitable films occur in the form of stacks of microscopically thin platelets in the outer layer of the barbules.
The dazzling iridescence seen on the crown, gorget, and breast of many hummingbirds is highly directional, appearing blackish when viewed from the side. It is caused by the mirror-like surfaces of the color-producing barbules. In the case of the vivid colors of the gorget, the “mirrors” concentrate the color so that it can be seen only from directly in front, as it would be seen by a territorial rival in a head-on confrontation. The brilliant gorgets of the Gorgeted Sunangel are good examples. Less brilliant colors result if the “mirrors” are curved so that the iridescence is scattered in all directions. For example, the iridescent greens seen on the body plumage of many hummingbirds, including the Sparkling Violetear, are less intense and can be seen from almost any angle.
Iridescent colors are rarely found in flight feathers, because the barbules that produce iridescence are modified and twisted in a way that weakens the feather structure. Iridescent flight feathers therefore do not stand up well to the stresses involved in the aerial acrobatics of a hummingbird. Nevertheless, iridescent flight feathers are found in a few species, notable examples being the Purple-throated Carib and the Great Sapphirewing.
Reprinted with permission from Hummingbirds: A Life-size Guide to Every Species by Michael Fogden, Marianne Taylor and Sheri L. Williamson and published by Harper Design, 2014. Buy this book from our store: Hummingbirds.