Chivi vireo

Appearance

The species looks similar to the related red-eyed vireo and yellow-green vireo. It is 12–14 cm in length, with the mass and length of the bill and wings varying in different subspecies.

Hatchlings are born almost naked with yellow skin and sparse down. Juveniles have brownish or tawny upperparts, with the greater and median coverts having brownish-green tips, and the head showing a less contrasting pattern than adults. The mouth lining is paler than adults up until 6 months of age. They may also show molt contrast on their wings.

Adult vireos are very similar, except in the subspecies ''diversus,'' where the female is smaller than the male. The crown is medium gray with thin but well defined gray borders, with a whitish supercilium extending above the ear coverts. The lores are a dull gray, and the nape, along with the side of the neck and the rest of the upperparts being a dull olive green. The area below the eyes is off-white in color. The wing coverts are dull gray brown, edged with olive green. The rectrices are green-gray in color, and have bright green edges. The undertail is very pale. The throat, breast, and belly are off-white or grayish-white in color, with a greenish tinge to the flank and sides of the breast. The upper mandible of the beak varies in color from black to blackish brown or a dusky gray, with the mandible being pale to blue-gray in color with a dark tip and paler base. The iris is brown in color, although it varies in shade from pale brown to reddish brown. The legs are pale brown to pale gray in color.

Naming

There are 9 subspecies of the chivi vireo:

⤷  ''V. c. chivi'' – The nominate, it is found in west and southwest Amazonia and south to central Argentina. It weighs 10.9–15.5 g , with a bill length of 11–13 mm and a wing length of 66–72 mm .
⤷  ''V. c. agilis'' – Found in east Brazil south through to Rio de Janeiro. It weighs 14.0–14.5 g . It is more brightly colored then the nominate, with a paler gray crown, the sides of the breast, flanks and vent being a brighter yellow.
⤷  ''V. c. griseobarbatus'' – Found in west Ecuador and northwest Peru. It weighs 13 g , with a bill length of 16–18 mm in males and 17–19 mm in females and a wing length of 62.5–71.5 mm . It tends to have a brighter green back than the nominate, with dark line bordering the crown and more yellow on the underparts, especially the flanks.
⤷ ''V. c. caucae'' – Found in west Colombia, on the Pacific coast, the western slopes of the West Andes and the valleys of the upper Río Patía and Río Cauca. It looks similar to the nominate subspecies, but is darker with more grayish ear coverts.
⤷ ''V. c. vividior'' Hellmayr & Seilern, 1913 – Found in Colombia, Venezuela, the Guianas, north Brazil and Trinidad. It weighs 12.8–21 g , with a bill length of 12–13 mm and a wing length of 71–75 mm . It has brighter yellow-green upperparts, with a relatively longer bill.
⤷  ''V. c. solimoensis'' Todd, 1931 – Found in east Ecuador, northeast Peru and extreme west Brazil. It weighs 12.5–15.0 g , with a bill length of 15–18 mm in males and 16–17 mm in females and a wing length of 60–68 mm . It is small, with a bright yellow behind, and the gray crown extending over to the hindneck.
⤷  ''V. c. tobagensis'' Hellmayr, 1935 – Found in Tobago. It is a large subspecies, with a heavy bill and a darker back.
⤷  ''V. c. diversus'' Zimmer, JT, 1941 – Found in east Paraguay, southeast Brazil, Uruguay and northeast Argentina. It weighs 15–17 g , with a wing length of 68.0–76.5 mm . Looks similar to ''agilis'', but has darker and duller upperparts, a brown-tinged back, and a mouse-gray on the top of the head. It is differs from ''chivi'' by having greener upperparts, flanks and sides, and a more yellow crissum .
⤷ ''V. c. pectoralis'' Zimmer, JT, 1941 – Found in north Peru, with a suspected population in Zamora-Chinchipe in southeastern Ecuador. Similar to ''griseobarbatus,'' but larger, with gray-tinged breast and throat and darker and duller green on the back.

Distribution

This bird is very widespread across most of northern, eastern, and central South America, with the exception of southern Chile and southern Argentina. Resident populations of the chivi vireo occur across northeastern Colombia, into Venezuela and the entirety of the Guianas into eastern Brazil. They also occur alongside many rivers in Amazonia, continuing into parts of Peru, Bolivia and Ecuador, with some resident populations inhabiting western Colombia. More migratory populations are found in south and southeastern Brazil, Paraguay, Bolivia, and Uruguay, along with the northern areas of Argentina. In the non-breeding season these populations travel north as far as Venezuela, eastern Colombia, eastern Ecuador, and eastern Peru.

It inhabits the canopy and subcanopy of dry to wet forests, along with borders, light woodland, restinga, gallery forest in the cerrado, dense scrub, small tree groves, and secondary growth with tall trees. It inhabits semi-deciduous, várzea and secondary forests in Peru, ascending into montane valleys in the south. In central Amazonian Brazil, the bird is not common in mature forests, with these habitats being inhabited by migrant red-eyed vireos. It has been recorded up to an elevation of 1,900 m in Bolivia and 2,600 m in Peru, but is usually only found up to an elevation of 1,500 m in Colombia and Brazil, and up to an elevation of 1,300 m in Ecuador. It can also inhabit highly disturbed and modified habitats as long as tall trees are present.

Status

The chivi vireo is listed as a least concern species by the IUCN. The species is common across its large range, and seems to have a stable population. The population may also be increasing locally. Also, its acceptance of disturbed habitat increases its chances of survival.

Behavior

The species is largely resident throughout its range, but in the south of its range, the subspecies ''chivi'' and ''diversus'' are known to be migratory. There are also some subspecies that are likely to undertake short migrations.

Habitat

This bird is very widespread across most of northern, eastern, and central South America, with the exception of southern Chile and southern Argentina. Resident populations of the chivi vireo occur across northeastern Colombia, into Venezuela and the entirety of the Guianas into eastern Brazil. They also occur alongside many rivers in Amazonia, continuing into parts of Peru, Bolivia and Ecuador, with some resident populations inhabiting western Colombia. More migratory populations are found in south and southeastern Brazil, Paraguay, Bolivia, and Uruguay, along with the northern areas of Argentina. In the non-breeding season these populations travel north as far as Venezuela, eastern Colombia, eastern Ecuador, and eastern Peru.

It inhabits the canopy and subcanopy of dry to wet forests, along with borders, light woodland, restinga, gallery forest in the cerrado, dense scrub, small tree groves, and secondary growth with tall trees. It inhabits semi-deciduous, várzea and secondary forests in Peru, ascending into montane valleys in the south. In central Amazonian Brazil, the bird is not common in mature forests, with these habitats being inhabited by migrant red-eyed vireos. It has been recorded up to an elevation of 1,900 m in Bolivia and 2,600 m in Peru, but is usually only found up to an elevation of 1,500 m in Colombia and Brazil, and up to an elevation of 1,300 m in Ecuador. It can also inhabit highly disturbed and modified habitats as long as tall trees are present.The species is largely resident throughout its range, but in the south of its range, the subspecies ''chivi'' and ''diversus'' are known to be migratory. There are also some subspecies that are likely to undertake short migrations.

Reproduction

The species nests in the austral spring in the south of its range, and in the middle of the year in the north. The populations in Venezuela, Tobago, and Colombia nest in May–June, while the populations of the nominate subspecies in Peru have been seen nesting in November. Brazilian populations are thought to nest in October–January.

Nests of ''vividior'' are generally built in a cup shape out of grass, vegetable fibers, and small amounts of plant down in a tree fork, while nests of ''griseobarbatus'' are cup-shaped structures built out of dry weeds, vines, and bark and lined with black lichen, feathers, and seed down. The nests of ''griseobarbatus'' had an external height and depth of 50 mm and 77 mm, with an internal height and depth of 31 mm and 52 mm.

Eggs are laid in clutches of 2–4 at a time. Eggs vary in appearance and size between different subspecies. The mean size of eggs in ''griseobarbatus'' is reported to be 22.0 mm × 13.1 mm , while that size of eggs in Brazil is 20.32 mm × 14.65 mm , and the size of eggs in Argentina being 18.5 mm–19.0 mm × 13.0 mm–14.5 mm . The average mass of eggs measured in southeastern Brazil was 2.27 g .

Eggs of ''vividior'' are white with some blackish spots on the larger end of the egg. Eggs of ''griseobarbatus'' are said to be white with sparse and faint markings. Eggs in eastern Brazil have been described as white. The eggs in northeastern Argentina have been described as being white and having gray or fine chestnut markings and dark lines which were concentrated at the larger end. The incubation period of the eggs is reported as being 10–16 days. Only females incubate the eggs. The nests are probably parasitized by shiny cowbirds. Eggs might also be eaten by snakes as one nest in Ecuador was observed being predated on by a snake. The nestling period is 10–13 days, and young are dependent on parents for a while after they have fledged.

Food

The species is primarily an insectivore, but some populations are known to consume fruit, and they may be important seed dispersers for some plants. It mainly consumes arthropods, especially caterpillars and other insect larva. They have been recorded consuming fruits of ''Myrsine coriacea, Rapanea lancifolia, Myrsine ferruginea, Trichilia spp., Cabralea canjerana, Talauma ovata, Davilla rugosa, Nectandra megapotamica, Byrsonima sericea, Miconia minutiflora, Cupania emarginata and oblongifolia, Zanthoxylum rhoifolium, Trema micrantha, Alchornea glandulosa,'' and ''Pera glabrata''. It is thought to be an important seed disperser for ''Cabralea canjerana.'' It is also suspected of being nectarivorous.