At the Zoo: Desert Hummers
by Alex Hawes
The doorway into the Smithsonian National Zoo’s Pollinarium exhibit draws visitors into a verdant habitat painted by the petals of heliconia, pentas, red salvia, blue porterweed, and other flowering plants. Butterflies float by on wings that flutter lazily in the silence. But if one listens carefully, the quiet may be interrupted by a faint hum—which blossoms into a buzz when a sprightly figure darts to the fore and hovers in mid-air. This airborne magician is none other than the Costa’s hummingbird (Calypte costae).
A male and female Costa’s hummingbird arrived at the National Zoo in April 2000. Last February, the female hatched two chicks, who soon joined their parents zipping through the exhibit. To advance zoo breeding efforts for the species and avoid possible conflict between father and son, the male chick was sent to the National Aviary in Pittsburgh in November. With the unexpected death of the father last spring, a male Costa’s from another institution may eventually join the remaining mother and daughter in hopes of breeding and further expanding the diversity of Costa’s in zoos.
Costa’s hummingbirds of both sexes shimmer with a greenish bronze hue across much of their bodies. The crown and gorget of males glisten in iridescent violet or magenta when the sun strikes at the right angle. About half of adult females display a tuft of purple on their throats. Female and young Costa’s are often mistaken for Anna’s hummingbirds (Calypte anna)—their closest relatives—in the field, confounding study of their distribution.
Wild Costa’s hummingbirds primarily range from southern Nevada, Arizona, and California to northwestern Mexico and Baja California. The birds are occasionally sighted as far north as British Columbia and even Alaska. The proliferation of birdfeeders and exotic plants in urban backyards could explain the Costa’s apparent expansion into the Pacific Northwest, while plantings of non-native tree tobacco (Nicotiana glauca) may have encouraged their recent spread eastward into parts of New Mexico and Texas.
Costa’s habitat includes chaparral, coastal scrub, desert washes, and other generally arid terrain. The hummingbirds migrate seasonally in search of various species of cacti, desert lavender (Hyptis emoryi), and other flowering plants. Those birds that inhabit the Sonoran Desert in the winter months, for example, often escape to the Pacific coast for summer. In the Sonoran, the favored red flowers of ocotillo (Fouquieria splendens) bloom fruitfully in early spring, while chuparosa (Justicia californica) flowers offer plentiful nectar throughout winter. (Fittingly, chuparosa is one of several words for hummingbird in Spanish.) Like most hummingbirds, Costa’s rely on nectar to fuel their high-energy lifestyle. These agile birds also snatch flies out of the air and may prey upon insects and spiders crawling on branches and tree trunks. At Pollinarium, Costa’s hummingbirds feed on fruit flies and a nectar blend rich in protein and carbohydrates.
The timing of Costa’s breeding varies with latitude and climate. Males emit a shrill whistle—once compared to “the highest and sharpest note that can be made on a violin”—to impress females during swooping display dives. Both males and females defend breeding and feeding territories (if nectar is not superabundant) as well as nesting sites. Females fabricate nests in shrubs several feet above ground, using spider webbing to hold nests in place and leaf litter for camouflage. They almost always lay two eggs, which incubate for 15 or 16 days on average. Young Costa’s first leave the nest at about three weeks of ago.
One of the smallest hummingbirds found in the United States, adult Costa’s weigh three grams on average (one-tenth of an ounce)—about as much as a penny. Their diminutive size, which allows the birds to shed excess heat, is likely an adaptation to their unforgiving, arid surroundings. Once the lords of these desert realms, Costa’s are increasingly finding company, however. University of Arkansas at Little Rock biologist William Baltosser, the foremost expert on Costa’s hummingbirds, speculates that people installing hummingbird feeders and exotic plants in their backyards are helping larger hummer species to muscle Costa’s out of parts of their historic range. Alteration and development of Costa’s habitat—particularly of California’s coastal scrub—and the planting of combustible, non-native grasses for cattle forage pose further threats to their survival as a species.
ZooGoer 31(2) 2002. Copyright 2002 Friends of the National Zoo. All rights reserved.
