Vireos and Peppershrikes (Vireonidae)

(vertebrate zoology) The vireos, a family of New World passeriform birds in the suborder Oscines.

(Vireonidae)

Class: Aves

Order: Passeriformes

Suborder: Passeri (Oscines)

Family: Vireonidae

Thumbnail description
A group of small, plain-colored songbirds of forests and woodlands; they feed by gleaning invertebrates from plants and may also eat small berries

Size
4–7 in (10–18 cm)

Number of genera, species
4 genera; 43 species

Habitat
A wide range of types of forests, woodlands, and shrublands, from boreal to humid tropical

Conservation status
Critically Endangered: 1 species; Endangered: 1 species; Vulnerable: 1 species; Near Threatened: 2 species

Distribution
Boreal regions of North America, tropics of Central and South America, and temperate woodlands of southern South America

Evolution and systematics

Vireonidae is comprised of 43 species of small arboreal songbirds, divided into four genera. The phylogenetic relationships of the Vireonidae with other families are not totally clear, but they appear to be closely related to the New World warblers (family Parulidae).

Vireonidae is divided into three subfamilies: the Vireoninae, consisting of the true vireos (genus Vireo) and greenlets (Hylophilus); the Cyclarhidinae or peppershrikes (Cyclarhis); and the Vireolaniinae or shrike-vireos (Vireolanius).

Physical characteristics

The vireos are small, plain-colored songbirds; the name vireo is derived from the Latin word for "greenish." The bird has a short, somewhat heavy, pointed beak, with a small hook at the end formed by the overhanging tip of the upper mandible. The wings may be rounded at the end, or may be more pointed. The legs are short but strong. Vireos are typically colored olive gray, olive brown, greenish, or yellowish above; they have a white, light gray, yellow, or yellow-washed breast and belly. Most species have a black line through the eye and a white stripe above it, but some have a light-colored eye-ring. A pale wing bar is generally present. The sexes are colored similarly.

Distribution

Vireos and their allies range widely over the Americas, from the boreal and temperate regions of North America, through the tropics of Central and South America, to the temperate woodlands of southern South America. They occur in northern Canada; throughout most of the United States, Mexico, and Central America; and in most of South America, as far south as Uruguay, northern Argentina, and northern Chile. Northern species of vireos are migratory, while those breeding in the tropics and subtropics are resident.

Habitat

These birds inhabit a wide range of forests and woodlands, including boreal, temperate, and tropical types.

Behavior

Vireos are usually solitary, or they appear as a breeding pair or family group. They sometimes participate in mixed-species foraging flocks during the nonbreeding season. They are deliberate but active birds. Their song is generally loud and melodic, and consists of several repeated phrases. Songs are varied and rather complex, and species may have from about 10 to more than 100 song types. The males sing frequently and persistently, often while foraging; they may even sing while on the nest.

Feeding ecology and diet

Vireos and their allies feed by gleaning insects, spiders, and other invertebrates from foliage, flowers, bark, and other plant surfaces. They also may eat small berries and other fruits.

Reproductive biology

Migratory species pair up soon after their arrival on the breeding grounds in the spring, with the male delimiting and defending the territory by song. The open, cup-shaped nest is made of spider and silkworm webbing, fine grass stems, other plant fibers, lichens, mosses, and feathers. The nest is usually located at the fork of a branch, hanging below the place of attachment, either close to the ground or high in the canopy.

The clutch size is two to five, and the eggs vary in color from whitish to speckled. Both sexes share in incubating the eggs and caring for the young. The incubation period is typically 12–14 days, and the nestlings fledge at nine to 11 days. The fledglings cannot fly well at first but are good at scrambling on branches and in shrubs. They are fed by the parents for about three weeks after leaving the nest.

Migratory species try to nest two to three times each season. Nesting vireos are highly vulnerable to parasitism by species of cowbirds, and to predation by small mammals, snakes, and predatory birds.

Conservation status

The IUCN lists five species in the Vireonidae as being at risk due to loss of habitat as a result of agricultural conversion of forest, logging, and other human activities. The Saint Andrew vireo (Vireo caribaeus) of the Caribbean island of Saint Andrew is listed as Critically Endangered. The Choco vireo (Vireo masteri) is known only from a tiny range in Colombia; it is Endangered because of the loss of most of its montane tropical rainforest habitat. The black-capped vireo (Vireo atricapillus) of Mexico and the southern United States is Vulnerable. The Noronha vireo (Vireo gracilirostris) of Brazil and the Blue Mountain vireo (Vireo osburni) of Jamaica are Near Threatened, but they too have suffered large population declines due to the loss and fragmentation of their habitats.

Significance to humans

Vireos and their allies are not of direct importance to humans. It is important that research be undertaken to better understand the biology and habitat needs of the rare and endangered species of vireonids.

Species accounts

Resources

Bent, A.C. Life Histories of North American Wagtails, Shrikes, Vireos, and Their Allies. New York: Dover Publications, 1965.

BirdLife International. Threatened Birds of the World. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, 2000.

Ridgely, R. S., and G. Tudor. The Birds of South America. Vol. 1. The Oscine Passerines. Austin: University of Texas Press, 1994.

Greenberg, R., D. K. Niven, S. L. Hopp, and C. A. Boone. "Frugivory and Coexistence in a Resident and Migratory Vireo on the Yucatan Peninsula." Condor 95, no. 4 (1993): 990–999.

Hopp, S. L., C. A. Boone, and A. Kirby. "Banding Returns, Arrival Pattern and Site Fidelity of White-Eyed Vireos." Wilson Bulletin 111 (1999): 46–55.

BirdLife International. Wellbrook Court, Girton Road, Cambridge, Cambridgeshire CB3 0NA United Kingdom. Phone: +44 1 223 277 318. Fax: +44-1-223-277-200. E-mail: birdlife@birdlife.org.uk Web site:

IUCN–The World Conservation Union. Rue Mauverney 28, Gland, 1196 Switzerland. Phone: +41-22-999-0001. Fax: +41-22-999-0025. E-mail: mail@hq.iucn.org Web site:

The Vireo Homepage. 2002.

[Article by: Bill Freedman, PhD; Melissa Knopper, MS]