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 birth mass: 1.5 to 1.8 g.
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: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
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)