Vireo olivaceus is a vocal species that is 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 delineate territory boundaries, and are only sung by males. Both sexes use a call described as a catbird-like mew usually used in aggressive encounters or when predators are near.
Vireo olivaceus also uses postures and body movements to visually communicate. These postures have been identified as Crest-erect Alert, Head-forward Threat, Tail-Fanning, and Gaping displays. All of these displays are used in aggressive encounters between either sexes and are usually followed by pecking if an individual does not retreat. Like all birds, red-eyed vireos perceive their environments through auditory, visual, tactile and chemical stimuli.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Currently, Vireo olivaceus 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.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
There are no known adverse effects of Vireo olivaceus on humans.
To some extent, Vireo olivaceus controls insect pest populations through it's insectivorous diet. Red-eyed vireos provide little economic benefit to humans.
As primarily insectivores, Vireo olivaceus 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.
Commensal/Parasitic Species:
Vireo olivaceus is primarily an insectivorous species, but also occasionally eats fruit. Diet changes seasonally from nearly exclusively insects during the spring and summer to nearly all fruit during the winter. Main food sources include butterfly larvae (Lepidoptera), beetles (Coleoptera), mosquitoes (Diptera), cicadas (Homoptera), wasps and ants (Hymenoptera), grasshoppers (Orthoptera) and dragonflies (Odonata). These vireos also consume snails (Mollusca) and spiders (Arachnida), 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 (Rubus), elderberries (Sambucus canadensis), Virginia creeper (Parthenosisus quinquefolia), sassafras (Sassafras albidum), spicebush (Lindera benzoin), dogwood (Cornus), northern arrowwood (Viburnum recognitum), northern bayberry (Myrica pensylvanica), and southern magnolia (Magnolia grandiflora).
Animal Foods: insects; terrestrial non-insect arthropods; mollusks
Plant Foods: fruit
Primary Diet: carnivore (Insectivore )
Vireo olivaceus is a migratory species that inhabits the Nearctic and Neotropical regions. During the non-breeding season, this species inhabits northeastern South America and is found east of the Andes Mountains as far south as Uruguay. In early spring, Vireo olivaceus travels north through southern Central America, along the Gulf coast and across Cuba, Haiti and the Dominican Republic. Vireo olivaceus breeds 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 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.
Biogeographic Regions: nearctic (Native ); neotropical (Native )
Vireo olivaceus prefers to breed in deciduous or mixed forest with dense canopy cover. In coniferous dominated stands they are most often found near riparian areas. 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, Vireo olivaceus 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.
These vireos are largely considered forest interior species but recent research is suggesting otherwise. Red-eyed vireos have been shown to select sites based on high levels of canopy cover and may be influenced very little by edge effect or fragmentation.
Range elevation: 0 to 3000 m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; forest ; rainforest
Other Habitat Features: urban ; riparian
The annual adult survivorship for Vireo olivaceus is estimated at 0.58. Survival rates for chicks post-fledging is much lower, estimated at 0.28. The oldest known red-eyed vireo was banded as an adult in 1963 and recaptured in 1972, making the individual at least 10 years old. Vireo olivaceus is not kept in captivity. 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.
Range lifespan
Status: wild: 10 (high) years.
Like all Vireo species, Vireo olivaceus is a small, perching songbird with relatively large, hooked bills. They measure 15.24 cm in length, feature a 25.4 cm wingspan, and weigh an average 18 g. Red-eyed vireos are recognized for their dark red irides 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 supercilium and a dark gray eye-line. Bills and legs are dark gray to black. Vireo olivaceus exhibits no sexual dimorphism and juveniles resemble adults, but are more gray-ish green overall.
Closely related species include Vireo flavoviridis and Vireo altiloquus. Their breeding ranges do not overlap, but they may overwinter in similar regions of South America. Vireo flavoviridis can be distinguished by brighter and more extensive yellow under tail coverts, flanks and cheeks. They also have a pale, larger bill as opposed to the dark smaller bill of Vireo olivaceus. Vireo altiloquus is overall brownish-green, with very pale yellow on the under tail coverts and flanks, as well as a defining black "whisker" or lateral stripe down the throat. Each of these species is best defined by song.
Average mass: 17 g.
Average length: 15.2 cm.
Average wingspan: 25.4 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Adult Vireo olivaceus 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.
Known Predators:
Anti-predator Adaptations: cryptic
Vireo olivaceus is a monogamous species, but the length of pair-bonds is currently unknown. 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. Red-eyed vireos have been observed to perform a "swaying" display, but this is currently hypothesized to be used to appease individuals rather than court.
Mating System: monogamous
Males arrive on the breeding grounds from mid-March to early May and immediately establish territories. First year individuals are able to breed. 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 after 10 to 12 days and reach independence after an additional 25 days when the parents stop providing food.
Breeding interval: Red-eyed vireos breed once yearly.
Breeding season: The breeding season for red-eyed vireos occurs from mid-April to August.
Range eggs per season: 3 to 5.
Range time to hatching: 11 to 14 days.
Range fledging age: 10 to 12 days.
Range time to independence: 35 to 37 days.
Average age at sexual or reproductive maturity (female): <1 years.
Average age at sexual or reproductive maturity (male): <1 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Male Vireo olivaceus 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 subsequent brooding of the young is also performed solely by the female. Hatchlings are altricial at birth, which requires significant parental care to feed, protect, and warm the defenseless young. Both parents actively consume or remove egg shells from the nest, which likely reduces the chance of predation by removing the scent of eggs. Fecal sacs are also removed by both parents, mostly by females, and are consumed until the 7th day post-hatch. 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 post-fledging, but then drastically decrease feeding until 25 days post-fledge when feeding ceases.
Parental Investment: altricial ; male parental care ; female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)
