Vireo atricapillablack-capped vireo

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Geographic Range

The range of V. atricapilla extends from Northern, Western and Central Texas to Northern Mexico. During the summer V. atricapilla breeds primarily in the Edward's Plateau of Central Texas. In the winter (non-breeding season), V. atricapilla can be found in the flatlands and Pacific foothills of Western Mexico (throughout the states of Sonora and Guerrero). (Scott 1987; Tveten 1987)

Habitat

In general, black-capped vireos prefer low thickets in scrub-oak woodlands, arid hilly regions and ledges on steep hills near water. It is believed that the largest known concentration of V. atricapilla can be found near Austin, Texas, located in the Edward's Plateau region which encompasses 17 % of the state of Texas. Geographically, this area consists of oak thickets combined with heavy ground cover as well as shallow, rocky canyons that receive abundant, bright sunlight. These places are described as "the hottest places imaginable", for birds at least. (Kutac 1989; Tveten 1987)

Physical Description

V. atricapilla is the smallest and most distinctly marked of all North American Vireos. This bird is fairly small with an average height of 11 cm and wingspan of 16.5 cm. This bird is unique in that it is the only North American bird to have white spectacles on a jet-black head. The female, however, has more of a slate-gray head coloration. Both males and females have red eyes and yellow to whitish wing bars. These birds are generally olive above and white below with yellow flanks. The female is smaller in size and juveniles are more brown above , rather than olive, and buffy below. Black-capped vireos are also distinctly different from all other New World, neo-tropical Vireos because of their quick action, bold patterns and quick flight. The flight of V. actricapillus is quick, nervous and rarely sustained. (Oberholser 1974; Tveten 1987; Scott1987)

Reproduction

V. atricapilla arrives at its breeding region in early March and has migrated south by late September. The actual breeding begins in mid-April and ends in early August. These birds are monogamous. The nests of the birds can be found in forked twigs of small trees or shrubs, usually 2-6 ft. up (rarely any higher). The actual nest is compact, cup-like and rounded in shape with thick walls. It is composed of leaves, coarse grasses, bark strips, catkins and spiders' cocoons, all bound together and supported with long plant fibers, spider webs and wool. The inside of the nest is lined with finer grasses. The nests are built by both males and females but the majority of the work is done by the female. The nest is built within six to nine days. Females have a clutch size of three to five eggs. The eggs of V. atricapilla are sub-elliptical to long sub-elliptical. On the exterior they are smooth but non-glossy, pure white and unmarked. Once again, black-capped vireos show their uniqueness in that their eggs are unmarked while all other vireos have spotted eggs. The average size of the egg is 18 x 13 mm. Incubation time ranges from 14 -17 days. Both males and females take turns in keeping the clutch warm. When the altricial nestlings hatch, they are naked with yellowish to pink skin. Males bring 75 % of the nestlings' food. They are fed for another four to seven days. The young leave the nest about ten to twelve days after hatching. Black-capped vireos have a success ratio of one to two chicks per two adult pairs. This low success ratio is attributed to female brown-headed cowbird nest parasitism. (Ehrlich et al 1988; Baicich & Harrison 1997; Tveten 1987, Oberholser 1974)

Behavior

V. atricapilla is easier heard than seen due to its secretive behavior. These birds prefer to hide within thick oak clumps where they feed and nest. Black-capped vireos rarely fly in the open unless migrating. The best locator of V. atricapilla is its song. The males sing throughout the breeding season, even in midday heat and while feeding. The song is characterized by a persistent string of hurried, twittering, varied two or three note phrases and is described as hurried, waspish and "restless, almost angry in quality". Its song is harsher than other vireos'. However, Black-capped vireos do not sing during flight. (Scott 1987; Tveten 1987; Oberholser 1974)

Communication and Perception

Food Habits

Black-capped vireos are active feeders that like to eat insects. Their diet consists primarily of caterpillars and beetles. Young birds seem to prefer spiders as a supplement to their diet while adults prefer berries. Both glean the insects from foliage in a "characteristic pose" of hanging upside down and then fluttering to a lower branch. (Tveten 1987)

Economic Importance for Humans: Negative

Economically, the decline in the population of the black-capped vireo has had a negative impact on humans in terms of restrictions on urban growth and development needed to meet the expanding demographics of the Central Texas area.

Conservation Status

In October of 1987 the U.S. Fish and Wildlife Service placed V. atricapilla on the endangered species list. These birds face extinction primarily because of nest parasitism by female brown-headed cowbirds. it is believed that up to 90 % of black-capped vireos' nests are infected by these brood parasites. The actual process shows that in most cases the female parasite will actually remove the hosts' eggs from an untended nest and then deposit her own. Even if the hosts' eggs are not removed, the vireos still have great odds against survival due to the fact that the incubation period of the brown-headed cowbird is shorter (10 - 12 days) than the Black-capped vireos (14 - 17 days). The hosts' eggs still have even greater odds against their survival if they do hatch because they rarely can compete for nest space and food with the older and larger cowbird hatchlings.

In addition, severe habitat loss, due to urbanization and over-browsing by animals, adds to the susceptibility to extinction of V. atricapilla. Before the 1950's, V. atricapilla was found in Kansas and Oklahoma, as well as in Texas. The last reported sighting of V. atricapilla in Kansas was in 1953.

Fortunately, habitat management and conservation is taking place at many Texas state parks and recreation areas in order to preserve the remaining and dwindling population. Also extermination, of some of the plentiful, brown-headed cowbird populations that take part in nest parasitism which in turn affects the reproductive success of the black-capped vireos, is currently taking place.

(Tveten 1987; Perrins & Middleton 1985; Robbins, Brunn & Zim 1983)

Contributors

Jessica Drake (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

visual

uses sight to communicate

References

Baicich, P., C. Harrison. 1997. A Guide to the Nests, Eggs and Nestlings of North American Birds, 2nd ed. San Diego: Academic Press/Natural World.

Ehrlich, P., D., Wheye, D.. 1988. The Birders Handbook: A field guide to the natural history of North American Birds. New York: Sunon and Shuster.

Kutac, E. 1989. Birder's Guide to Texas. Houston, Texas: Lonestar Books.

Oberholser, H. 1974. The Bird Life of Texas. Austin & London: University of Texas Press.

Perrins, D., D. Middleton. 1985. The Encyclopedia of Birds. New York: Facts on File Publishing.

Robbins, C., B. Brunn, H. Zim. 1983. A Guide to Field Identification, Birds of North America. New York: Golden Books.

Scott, S. 1987. Field Guide to the Birds of North America, 2nd ed. Washington, D.C: National Geographic Society.

Tveten, J. 1993. The Birds of Texas. Fredericksburg, Texas: Shearer Publishing.