Black-throated Green Warbler Life History

Habitat

Habitat Forests

The Black-throated Green Warbler occurs in a wide variety of forest habitats. They nest in conifer forests in the northwest of their range, mixed hardwoods forests in the southern Appalachians, and cypress swamps on the mid-Atlantic coast. Wintering birds are most common in the canopies of tall forests.

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Food

Food Insects

They eat almost exclusively insects during the breeding season, especially caterpillars, which they glean from small branches on both coniferous and deciduous trees. They also take berries in migration and feed on the buds of cecropia trees while wintering in the tropics.

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Nesting

Nest Placement

Nest Tree

The female chooses the nest site, which is usually 3-10 feet off the ground (sometimes much higher) in a small tree or sapling, and is located close to the trunk. The "Wayne's" subspecies often nests higher up and farther from the trunk, in a cypress, oak, or magnolia.

Nest Description

The nest is small and cup-shaped, made of twigs, bark, and spider silk and lined with hair, mosses, and feathers. Finished nests are 3–4 inches in diameter and about 2 inches tall. The female does most of the nest building, taking 4–8 days to complete the task.

Nesting Facts
Clutch Size:3-5 eggs
Number of Broods:1 brood
Egg Length:0.6-0.7 in (1.5-1.8 cm)
Egg Width:0.5-0.5 in (1.2-1.3 cm)
Incubation Period:12 days
Nestling Period:8-11 days
Egg Description:

Whitish with variable brown blotches or speckles.

Condition at Hatching:

Helpless with sparse down.

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Behavior

Behavior Foliage Gleaner

Black-throated Green Warblers hop through arboreal vegetation, flying between trees but seldom above trees. The males are aggressive when on territory, attacking and chasing rivals. This is sometimes followed by the victor undertaking a shallow, mothlike flight. Males singing on territory often choose an exposed perch from which their yellow head will be conspicuous. Pairs are seasonally monogamous, remaining together until shortly after the young leave the nest. In fall migration this species often forms mixed-species flocks with other species of southbound warblers and resident songbirds. Black-throated Green Warblers also join mixed flocks of tropical species in winter.

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Conservation

Conservation Low Concern

Black-throated Green Warblers are common and their populations increased by an estimated 41% between 1970 and 2014, according to Partners in Flight. The group estimates a global population of 8.7 million and assigns the species a Continental Concern Score of 9 out of 20. It is not on the Watch List, meaning it is a species of low conservation concern. The largest conservation issue for Black-throated Green Warblers is habitat degradation and loss. Despite its expansive breeding range, Black-throated Green Warblers are more commonly found in forest interiors than edges, so they’re susceptible to fragmentation. Invasive insects like woody adelgids have also caused the widespread death of conifers in some parts of the species’ range, leading to the disappearance of local populations in affected areas. Deforestation on the tropical wintering grounds removes some wintering habitat, although Black-throated Green Warblers will use native canopy trees on shade-grown coffee plantations or logged areas provided that some emergent vegetation remains.

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Backyard Tips

Black-throated Green Warblers are not typically a backyard bird and don’t come to feeders, but yards with large mature trees may host them in migration.

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Credits

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Morse, Douglass H. and Alan F. Poole. (2005). Black-throated Green Warbler (Setophaga virens), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

North American Bird Conservation Initiative. (2014). The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

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

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxtent Wildlife Research Center (2014b). Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

Stephenson, T. and S. Whittle (2013). The Warbler Guide. Princeton University Press, New Jersey, USA.

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