Like all Vireo species, red-eyed vireos are small, perching songbirds with relatively large, hooked bills. They measure 15.2 cm in length, feature a 25.4 cm wingspan, and weigh an average 18 g. Red-eyed vireos are recognized for their dark red eyes that adults feature. However, this characteristic is rarely seen in the field as they are often at the tops of trees. They are olive-green across the nape, back, wings and tail. Throat, breast, and belly are bright white, while the under tail coverts and flanks are pale yellow. These vireos have a gray crown with a contrasting thick, white stripe above their eye and a dark gray stripe through their eye. Bills and legs are dark gray to black. Males and females look alike and juveniles also resemble adults, but are more gray-ish green overall. (Cimprich, et al., 2000; Sibley, 2000)
Red-eyed vireos are migratory birds that inhabit North, Central, and South America. During the non-breeding season (winter), this species inhabits northeastern South America and is found east of the Andes Mountains as far south as Uruguay. In early spring, red-eyed vireos travel north through southern Central America, along the Gulf coast and across Cuba, Haiti and the Dominican Republic. Red-eyed vireos breed across nearly all of the United States, excluding the southwest region. Red-eyed vireos are rarely found south of Oregon or west of Colorado. Their breeding range extends as far north as the Northwest Territories in Canada and stretches from nearly coast to coast across southern Canada. Some Vireo olivaceus populations remain in South America to breed and move as far south as northern Argentina, but stay east of the Andes Mountains. Red-eyed vireos are common breeders during the summer in forests across Michigan. (Cimprich, et al., 2000; Sibley, 2000)
Red-eyed vireos prefer to breed in deciduous or mixed forest with dense canopy cover. In pine forests they are most often found near rivers or streams. They also breed in forested urban parks or cemeteries with old-growth trees that provide a dense canopy. They may be found anywhere from sea level to 2,000 m above in the Rocky Mountains.
In migration, red-eyed vireos can be found in habitats similar to those used for breeding. They visit a slightly broader range of habitats during migration and may be found in forest edge, second growth forest, or citrus groves.
During the non-breeding season, red-eyed vireos prefer rain forests, second growth forests, plantations and forest edge habitats. They select habitats located from sea level to 3,000 m above. (Cimprich, et al., 2000; Dunford, et al., 2002; Siepielski, et al., 2001)
Red-eyed vireos are monogamous, meaning that one male and one female pair together to breed and raise young. It is currently unknown if the same pairs form every year. Males arrive early at the breeding grounds to establish territory and pair formation occurs shortly after the females arrive. No courtship rituals have been observed, but males often chase potential mates and occasionally pin the females to the ground. (Cimprich, et al., 2000; Nolan, 1962)
Males arrive on the breeding grounds from mid-March to early May and immediately establish territories. Red-eyed vireos can breed as young as 1 year old. Females arrive 3 to 15 days later and select a nesting site within a male's territory. Nests are generally constructed in the crook of a branch in the mid- to understory layer. The most successful nests are well concealed from above by foliage. Female red-eyed vireos build the cup-shaped nests using grasses, twigs, roots, bark strips, or spiderwebs. The females line their nests with softer materials such as grass, pine needles, and occasionally animal hair.
Once the nest is constructed, females lay an average clutch of 4 white, spotted eggs. Females perform all incubation which lasts between 11 and 14 days. After the young hatch, they are tended by both parents. The tiny hatchlings initially weigh between 1.5 and 1.8 g. The young fledge (leave the nest) after 10 to 12 days and reach independence after an additional 25 days when the parents stop providing food. (Cimprich, et al., 2000; Ehrlich, et al., 1988)
Male red-eyed vireos invest time and energy in establishing suitable nesting territories. Males frequently engage in chases and physical aggression to defend their territories. Once females arrive, they provide the majority of parental care. Females select suitable nesting sites and complete all nest construction. Incubation and later brooding of the young is also performed solely by the female. Hatchlings are altricial at birth, meaning they are featherless with eyes closed and are unable to move. These defenseless chicks need a lot of care from their parents, who must warm, feed, and defend their young for several weeks. Both parents actively consume or remove egg shells from the nest, which likely reduces the chance of predation by removing the scent of eggs. Males contribute to feeding the hatchlings, but females provide the majority of food. Parents continue to feed the young frequently until 15 or 16 days after the young fledge, but then drastically decrease feeding until 25 days after fledging when parents stop feeding altogether. (Cimprich, et al., 2000)
The oldest known red-eyed vireo was banded as an adult in 1963 and recaptured in 1972, making the bird at least 10 years old. Just over half of all adult red-eyed vireos survive each year. Only 1 out of 4 chicks survive after leaving the nest. Causes of mortality are poorly understood but likely include parasites, brood parasitism, predation, and stress of long-distance migration. Many birds do not survive migration and perish in collisions with buildings or other tall objects during night journeys. Red-eyed vireos are not kept in captivity. (Cimprich, et al., 2000; Klimkiewicz, et al., 1983; Noon and Sauer, 1992)
Red-eyed vireos are Neotropical migrants that perform long-distance migrations twice yearly between North and South America. On migratory flights, these birds are nocturnal and will join mixed species groups or groups with up to 30 other vireos. They may stay in mixed species groups on the wintering grounds in South America, but they are solitary and territorial during the breeding season. Red-eyed vireos are more aggressive than most birds and will chase or physically attack others of either gender. They spend much of their time in the upper to mid canopy levels of dense forest, and are most active during dawn and dusk during the breeding season. (Cimprich, et al., 2000)
During the breeding season, males defend a territory that ranges in size from 0.86 to 3.71 hectares. Females will travel slightly outside of their mates' territory. Territory size appears to be density dependent, as when more males inhabit an area, their individual territory sizes shrink. (Cimprich, et al., 2000)
Red-eyed vireos are vocal birds that are frequently heard calling from the upper forest canopy. Their primary call is mostly two-note phrases that are mnemonically described as "Look up! See me? Over here! Do you hear me?" Male red-eyed vireos are one of the most persistent singers of all birds and have been recorded singing 10,000 songs in one day. These songs are used to announce territory boundaries, and are only sung by males. Both genders use a call described as a catbird-like mew usually used in aggressive encounters or when predators are near.
Red-eyed vireos also use postures and body movements to visually communicate. These postures consist of raising head and crest feathers, thrusting heads forward, fanning tail feathers or holding their mouths open wide. All of these displays are used in aggressive encounters between two males, females, or a male and a female. If one of the birds does not retreat, these body movements are usually followed by pecking at each other. Like all birds, red-eyed vireos perceive their environments through the senses of sight, sound, touch, taste, and smell. ("Whatbird.com: Field Guide to Birds of North America", 2007; Cimprich, et al., 2000)
Red-eyed vireos are primarily insectivores, but also occasionally eat fruit. Diet changes seasonally from nearly exclusively insects during the spring and summer to mostly fruit during the winter. Main food sources include butterfly larvae, beetles, mosquitoes, cicadas, wasps and ants, grasshoppers and dragonflies. These vireos also consume snails and spiders, although rarely. Red-eyed vireos are foliage gleaners and capture insects setting on leaves or stems while perched, flying or hanging upside-down. There have been a few observations of red-eyed vireos drinking water that had collected on leaves.
Fruits and trees often utilized by red-eyed vireos include dewberries, elderberries, Virginia creeper, sassafras, spicebush, dogwood, northern arrowwood, northern bayberry, and southern magnolia. (Cimprich, et al., 2000)
Adult red-eyed vireos are occasionally preyed upon by sharp-shinned hawks. Eggs and nestlings are significantly more vulnerable than adults and are predated by many species including American crows, blue jays, common grackles, eastern chipmunks, and red squirrels. Red-eyed vireos employ aggressive swooping and pecking to deter predators. Some incubating females crouch into the nest, remain motionless, and rely on their olive coloration as camouflage. Both males and females produce catbird-like mews or "myaahs" when intruders near their nests. (Cimprich, et al., 2000)
As primarily insectivores, red-eyed vireos impact the insect populations they prey upon. Adults, young, and eggs may all be preyed upon and may support local predators. Red-eyed vireos also serve as hosts to parasites such as protozoan blood parasites, feather lice, mites, and hippoboscid flies. Red-eyed vireo nests are often parasitized by brown-headed cowbirds, usually resulting in nest failure. Vireos have on occasion buried the cowbird eggs and built a new nest over top, but this behavior is rare. (Cimprich, et al., 2000; Ehrlich, et al., 1988)
There are no known negative effects of red-eyed vireos on humans.
To some extent, red-eyed vireos control insect pest populations through their insectivorous diets. Red-eyed vireos provide little economic benefit to humans. As one of the most vocal bird species, red-eyed vireos' frequent songs are enjoyed by many bird watchers.
Currently, red-eyed vireo populations are stable and distributed across a wide geographic range. For these reasons, they are of least concern to conservation organizations. As migratory birds, red-eyed vireos are protected under the United States Migratory Bird Act. Although these birds are currently abundant and can tolerate low levels of habitat destruction, large-scale habitat changes can result in local extinctions. Red-eyed vireos have been shown to tolerate selective harvesting or small areas of clear-cutting that only cause small canopy openings. Any activity that significantly reduces canopy cover (extensive clear-cutting, strip mining, cultivating) can cause red-eyed vireos to abandon the area for 20 to 30 years. If these activities must occur, efforts should be made to leave adequate canopy cover and find a balance between human resource use and environmental protection. (Cimprich, et al., 2000)
Rachelle Sterling (author), Special Projects, Tanya Dewey (editor), University of Michigan-Ann Arbor.
2007. "Whatbird.com: Field Guide to Birds of North America" (On-line). Red-eyed Vireo. Accessed March 17, 2011 at http://identify.whatbird.com/obj/573/_/Red-eyed_Vireo.aspx.
Cimprich, D., F. Moore, M. Guilfoyle. 2000. "The Birds of North America Online" (On-line). Red-eyed Vireo (Vireo olivaceus). Accessed March 16, 2011 at http://bna.birds.cornell.edu/bna/species/527.
Dunford, W., D. Burke, E. Nol. 2002. Assessing edge avoidance and area sensitivity of red-eyed vireos in Southcentral Ontario. The Wilson Bulletin, 114/1: 79.
Ehrlich, P., D. Dobkin, D. Wheye. 1988. The Birder's Handbook. New York: Simon and Schuster.
Klimkiewicz, M., R. Clapp, A. Futcher. 1983. Longevity records of North American birds: Remizidae through Parulinae. Journal of Field Ornithology, 54/3: 287-294.
Nolan, V. 1962. The swaying display of the Red-eyed and other Vireos. The Condor, 64: 273 - 276.
Noon, B., J. Sauer. 1992. Populations models for passerine birds: Structure, Parameterization, and Analysis. Pp. 441–464 in D McCullough, R Barrett, eds. Wildlife 2001: Populations. New York, New York: Elsevier Applied Sciences. Accessed March 17, 2011 at http://gis.fs.fed.us/psw/publications/noon/noon8.pdf.
Sibley, D. 2000. The Sibley Guide to Birds. New York: Alfred A. Knopf.
Siepielski, A., A. Rodewald, R. Yahner. 2001. Nest site selection and nesting success of the Red-eyed Vireo in Central Pennsylvania. The Wilson Bulletin, 113/3: 302.