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Status: Population size: 3.6 million Photo by Bob Steele.

Costa's Hummingbird
(Calypte costae)

Costa's Hummingbird is a desert species restricted to the far southwest and retreating just south of the border in winter months. Adult males have an extravagant loop and dive display that tells other birds its species and fitness. Its total distribution in both breeding and nonbreeding seasons is small. This, combined with widespread habitat destruction and alteration, has landed this bird on the Audubon WatchList.

Identification
Costa's have a light green back lacking rufous coloring on its short tail. Adult males have an iridescent purple crown and gorget (throat patch) that extends down around the outside of the chest (flared). Adult male Anna's have more red in their crown and gorget and their gorget is not flared. Female Costa's has gray underparts and may have a purple spot in the center of her throat. Females and juveniles are difficult to distinguish from Black-chinned and Anna's Hummingbirds.

Adult males can be identified by their unique courtship display composed of three parts. The male first flies toward the object of the display (usually an adult female) and makes several passes over her. He then climbs steeply before making several vertical loops during which the male whistles. Loops can be 25-40 m high. The male finishes by zigzagging away from the female parallel to the ground. He shows up nearby soon afterwards and may repeat the sequence. He also whistles while perched, another way he can be identified in the field.

Distribution and Population Trends
Occurs mainly in Southern California, Arizona, Baja California, and western Mexico, but also extends into Nevada, extreme southeastern Utah, and southeastern New Mexico. Their range is expanding into new and historically occupied areas in parts of Arizona and California. Vagrants have been increasingly reported since 1970, but could be due to increased interest in hummingbirds. Christmas Bird Counts in Cabeza Prieta National Wildlife Refuge show greater abundance of Costa's during wetter years when chuparosa and desert lavender bloom. California coastal scrub habitat has been nearly completely eradicated, undoubtedly resulting in destruction of local Costa's populations. This species is a resident of the Sistema de Islas Sierra Madre Occidental and a winter resident of Cuenca del Rio Yaqui, two Mexican Important Bird Areas.

Ecology
Costa's are most abundant in the deserts of southern California and Arizona from March to April at the height of the breeding season. Females care for the young on their own, as is custom among hummingbirds. Nests are built in shrubs and trees with variable cover, depending on climate and dominant vegetation. The nests are located only 1-2 m above ground and are usually shallow, loosely constructed, and flimsy. A clutch of two is laid anywhere from February to May, depending on location, and incubated for 15-18 days, with young fledging 20-23 days later. A second clutch is attempted if the first one fails. By late June they have dispersed to coastal habitats.

Habitats occupied by Costa's Hummingbirds include Sonoran desert scrub, the Mojave desert, California chaparral, California coastal scrub, and the Cape deciduous forest of Baja California. It consumes nectar and insects, the latter which it captures by flycatching or by gleaning from vegetation. The migratory patterns for Costa's Hummingbird are complicated and not thoroughly studied, but some birds move to coastal California and Baja during the warmer summer months after breeding is completed and it generally contracts its range in colder months to the southern portion of the range within Mexico.

Threats
Costa's relies on several habitats threatened by development such as the endangered California coastal scrub habitat. The Sonoran desert scrub habitat is the largest and most intact habitat used by Costa's, but development is a threat here as well, where the rate of development is increasing. Desert scrub is being cleared for agriculture and flood control along major rivers. South African bufflegrass is planted widely in desert scrub for cattle grazing, a plant that fuels fires, thus wiping out native flowers and nesting trees that are not fire-resistant. Intensive cattle grazing in other habitats has unknown effects on Costa's. While hummingbirds can adapt to bird feeders and ornamental plants, Anna's probably outcompetes Costa's in such places. The extent of use of urban areas by this species is not well known. Costa's is known to hybridize with Calliope, Anna's, Black-chinned, and Broad-tailed Hummingbirds, which can dilute the gene pool of each of these species.

Conservation
Habitat management is of utmost priority for this species. Natural habitats need to be preserved and restored. This can be achieved by removal of invasive species such as bufflegrass and prevention of fires in desert scrub. Costa's might also benefit from frequent, natural burns in California chaparral, where it nests in shrubs.

Partners in Pollination/Alianza para Polinizacion, a consortium of non-profit organizations, universities, and businesses, was formed in 1995 to increase awareness of the importance of pollinators to ecosystems, encourage research and conservation on plant/pollinator interactions, and influence policy related to plant/pollinator conservation.

The Arizona-Sonora Desert Museum's Migratory Pollinators and Their Corridors project is working to educate, develop community stewardship, and conservation for plant/pollinator systems in the U.S. and Mexico (http://www.desertmuseum.org/conservation/mp/polpart.html).

What Can You Do?
Audubon's Important Bird Areas program is a vital tool for the conservation of Costa's Hummingbirds as well as other species. To learn more about the Important Bird Areas program, and how you can help, visit: http://www.audubon.org/bird/iba/.

Information on where Costa's Hummingbirds occur and in what numbers is vital to conserving the species. Help in monitoring this and other species by reporting your sightings to eBird. A project of Audubon and the Cornell Lab or Ornithology, eBird is the world's first comprehensive online bird monitoring program: http://www.audubon.org/bird/ebird/index.html.

Volunteers are also crucial to the success of long-term monitoring programs such as the Breeding Bird Survey (BBS). The BBS helps determine the distribution of species such as the Costa's Hummingbird and monitors population trends. To find out how you can get involved, log on to: http://www.mp2-pwrc.usgs.gov/bbs/participate/.

The Southeastern Arizona Bird Observatory has a hummingbird banding station on the San Pedro River. Their website not only provides information about hummingbirds, but the station also offers hummingbird workshops for visitors, including one on hummingbird banding and one on hummingbird identification. For more information, visit: http://www.sabo.org/hummers.htm.

References
Baltosser, W. H. and P. E. Scott. 1996. Costa's Hummingbird (Calypte costae). In The Birds of North America, No. 251 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D. C.

Kaufman, K. 1996. Lives of North American Birds. Houghton Mifflin Company, New York.

Sibley, D. A. 2000. The Sibley Guide to Birds. National Audubon Society. Chanticleer Press, New York.