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Black-capped Vireo Life History

Habitat

Habitat Scrub

Black-capped Vireos nest in low, scrubby vegetation, chiefly oak scrub, with scattered plants at a variety of heights. Dense, head-high vegetation is a common aspect of their many different nesting areas. This kind of habitat usually occurs on poor, sandy or rocky soils, often in ravines or canyons. Black-capped Vireos sometimes use successional growth that comes back after fires or other disturbances. Although Black-capped Vireos nest in oak-juniper habitats, specifically places with eastern redcedar and Ashe juniper, they’re more likely in areas dominated by oaks, including blackjack, shin, Vasey, Spanish, and plateau live oaks. In these habitats are also plants like Texas persimmon, southern hackberry (sugarberry), roughleaf dogwood, redbud, flameleaf sumac, and evergreen sumac. After the breeding season, a few Black-capped Vireos move into more arid environments, taller forests, and stream corridors. Wintering birds in western Mexico inhabit arid, scrubby foothills and canyons.

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Food

Food Insects

Black-capped Vireos eat mostly insects and their larvae, which they pick from leaves, twigs, and smaller branches, especially in oaks. They sometimes hover briefly to grab prey, and on occasion hang upside-down to inspect dead-leaf clusters for insect larvae. Males tend to forage a bit higher in trees than females. Their diet consists of adult and larval moths, butterflies, beetles, and flies, katydids, and spiders, along with small amounts of plant matter.

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Nesting

Nest Placement

Nest Tree

Male and female visit possible nest sites together, though the female probably makes the decision and does most of the inspection. Males build multiple starter nests in the territory, but the actual egg nest is usually in a different location and built mainly by the female. Nests are set in forks of branches, about 3 feet off the ground, in small scrubby trees or bushes, typically in small oaks.

Nest Description

Both male and female build the nest, but the female does most of the work, constructing an open cup made of leaves, grasses, plant fibers, and plant down, lined with grasses and camouflaged with paper, string, snake skin, feathers, spider cocoons, and other oddments. Nests average about 2.2 inches across and 2.3 inches tall, with interior cup about 1.8 inches across and 1.5 inches deep.

Nesting Facts

Clutch Size:2-5 eggs
Egg Description:

Smooth and white.

Condition at Hatching:

Naked and pink, with eyes closed.

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Behavior

Behavior Foliage Gleaner

Male Black-capped Vireos arrive on the breeding ground before females and immediately establish territories by singing and defending against rivals, even chasing them hundreds of feet in the air. Territory sizes vary considerably, from 2.5 to 25 acres or more. Females choose mates by inspecting both the males and their territories. Males perform courtship displays that involve opening and quivering the wings and singing in horizontal posture. (Threat displays against other males look similar.) In a seldom seen but remarkable courtship display, the male fluffs up his body feathers (revealing a striking underwing pattern in black and yellow at the bend of the wing), rears back on the perch to near a tipping point, and shows off each side of the face rhythmically to the female. Males also perform courtship flights, fluttering in an arc away from females, which may follow. Once paired, males guard females closely until she has laid eggs. Females also chase away other females. Black-capped Vireos have a complex mating system. A territorial male may partner with a female that remains with him through the fledging of the young. But a paired female may also leave the territory while young are still in the nest to partner with another male. In some cases, the female may return to help the male finish raising the young birds, but in other cases, she leaves the male to feed their young on his own. Females also sometimes depart the male’s territory and bring the young with her as she pairs with a different male on another territory. Likewise, males may court and mate with more than one female in a breeding season. After eggs have hatched, territorial males sometimes tolerate the presence of young males (with gray napes) in the territory. After the breeding season, most Black-capped Vireos apparently forage alone rather than remaining in family groups.

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Conservation

Conservation Red Watch List

Black-capped Vireos are scarce, and the species was federally listed as Endangered in 1987 in the United States. In 2018, after extensive conservation efforts, it was removed from the list. Partners in Flight estimates that the U.S. breeding population is 11,000, rates the species a 16 out of 20 on the Continental Concern Score, and includes it on the Yellow Watch List for species with restricted ranges. Major threats include habitat loss and fragmentation because of agricultural and residential development. Nest parasitism by Brown-headed Cowbirds has also had a devastating impact on vireo populations, but conservation efforts to control cowbird populations has helped to reduce that impact. Habitat maintenance and habitat creation through prescribed burning are also positive management tools. Fire suppression is a serious threat to this species, as it encourages maturation of oak-juniper scrub into juniper habitats that the vireo cannot use for nesting.

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Credits

Grzybowski, Joseph A. (1995). Black-capped Vireo (Vireo atricapilla), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2019. Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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