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Wilson's Warbler

Cardellina pusilla ORDER: PASSERIFORMES FAMILY: PARULIDAE

IUCN Conservation Status: Least Concern

Wilson’s Warblers dance around willow and alder thickets, often near water, to the rapid beat of their chattering song. This bright yellow warbler with a black cap is one of the smallest warblers in the U.S. and among the most recognizable. They rarely slow down, dashing between shrubs, grabbing insects from one leaf after another, and popping up on low perches to sing. Wilson's Warblers breed in mountains and northern forests, but pass through every state in the lower 48 during migration—so be on the lookout when they are on the move in the spring and fall.

At a GlanceHelp

Measurements
Both Sexes
Length
3.9–4.7 in
10–12 cm
Wingspan
5.5–6.7 in
14–17 cm
Weight
0.2–0.4 oz
5–10 g
Relative Size
Larger than a Ruby-crowned Kinglet, smaller than a Common Yellowthroat.
Other Names
  • Paruline à calotte noire (French)
  • Chipe coronoa negra, Reinita Gorrinegra, Reinita de Wilson, Chipe Careto, Reinita de Capucha, Chipe Coroninegro (Spanish)

Cool Facts

  • The majority of Wilson’s Warblers nest on the ground, except for populations in coastal California and Oregon where they nest up to 5 feet off the ground. These birds also tend to lay fewer eggs per nest compared to their ground-nesting relatives.
  • The Wilson's Warbler is found in a large diversity of environments in the winter. It is the only migrant warbler regularly found in tropical high plains (paramo).
  • Naturalist Alexander Wilson, often called the "father of American ornithology," described the Wilson’s Warbler in 1811 which he called the “green black-capt flycatcher.”
  • When most songbird nestlings are ready to leave the nest, they hop out and don’t return to the nest, but some Wilson’s Warbler fledglings head back to the nest for a night or two after fledging.
  • Wilson’s Warblers tend to be brighter yellow in the West and paler yellow in the East. Pacific Coast populations have the brightest yellow, almost orange, foreheads and faces. Rocky Mountain and Alaskan birds also tend to be slightly larger than the Eastern and Pacific Coast populations.
  • During spring migration, Wilson’s Warblers en route to Alaska to breed are the last ones to pass through the southwestern U.S. Birds that eventually breed in coastal California pass through Arizona first, followed by birds headed to the Pacific Northwest and the Sierra Nevada Mountains, and finally birds headed to Alaska. Read more about how scientists are using DNA to study Wilson's Warbler migration.
  • For decades biologists grouped Wilson’s Warblers into three subspecies, but a recent genetic study indicates that there could be 6 distinct breeding groups of Wilson’s Warblers and these 6 groups tend to segregate on the wintering grounds. Birds breeding in eastern Canada spend the winter mostly in the Yucatan Peninsula, while those breeding in the Pacific Northwest, the Sierra Nevada, and coastal California spend the winter in Baja California Sur and along the west coast of Sinaloa, Mexico.
  • The oldest recorded Wilson's Warbler was a male, and at least 8 years, 11 months, when he was recaptured and rereleased during banding operations in California in 2008. He had been banded in the same state in 2000.

Habitat


Scrub

Wilson’s Warblers breed across Canada and the western United States in willow, alder, and shrubby thickets near streams up to about 11,500 feet. They also use forest edges or forest openings with a dense understory of flowering plants such as aspen stands. In the Pacific Northwest they breed in young conifer, maple, and alder forests as well as scrubby patches of coyotebush and blackberry. Wilson’s Warblers key in on forests and scrubby areas along streams to fatten up during migration. During the nonbreeding season they use many types of habitats from lowland thickets near streams to high-elevation cloud forests in Mexico and Central America. They are one of a few migrant warblers that use high-elevation treeless plains (paramo) in Costa Rica.

Food


Insects

Wilson’s Warblers pick larval insects, spiders, beetles, and caterpillars off leaves and twigs. They also hover or sally (fly out and back) to grab flies, bees, mayflies, aphids, and other insects from leaves or in the air. They do most of their foraging in the understory in willows, alders, or other shrubs. On the wintering grounds they also drink "honeydew"—a sweet liquid excreted by scale insects as they feed on oak trees. Wilson’s Warblers hover near the insects and drink the sugary water for a few quick calories.

Nesting

Nesting Facts
Clutch Size
2–7 eggs
Number of Broods
1-2 broods
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
10–13 days
Nestling Period
9–11 days
Egg Description
White to creamy white with fine reddish brown speckling or spotting.
Condition at Hatching
Eyes closed and mostly naked with one or two tufts of down on the head or back.
Nest Description

Females use large leaves or sedges to form the base of the nest. Once the base is in place, they add moss, strips of bark, fine plant material, grass, and hair to make a cup-shaped nest in a little depression on the ground. Nests in shrubs are generally wedged between small twigs to keep them in place. It takes the female about 5 days to complete a nest without any help from the male. Ground nests are 3–4 inches wide with an interior cup of about 1–2 inches wide; nests in shrubs are slightly larger.

Nest Placement

Ground

Female Wilson’s Warblers tuck their nests in small depressions on the ground typically at the base of a tree sapling, willow stem, flowering plant, dense clump of grass, or log so that it is well hidden. Although most Wilson’s Warblers nest on the ground, those that live in coastal California build their nests as high as 5 feet above the ground in shrubs.

Behavior


Foliage Gleaner

Wilson’s Warblers are always on the move, either hovering to grab an insect or flitting to and fro in the understory, often twitching their tail. Unlike many other warblers, they spend much of their time foraging in low to middle levels of the forest. Males choose and defend territories that include nesting and foraging habitat. When another Wilson’s Warbler enters their territory they drop their wings and cock their tails upwards while hopping between branches and giving harsh calls. They typically mate with one partner during the breeding season, but like many other warbler species, some sneak off to mate with an additional mate, a phenomenon known as extra-pair copulation. Pairs typically break up after the summer and they find new mates in the following years. Only females incubate and brood eggs and nestlings, but males help with feeding nestlings and fledglings. If an adult detects a nest predator such as a Steller’s Jay near the nest, the parent may perform a broken-wing display to distract the predator. Other nest predators include mice, squirrels, chipmunks, domestic cats, and snakes. Many males and females defend territories on the nonbreeding grounds in Mexico and Central America, others join foraging flocks with other species.

Conservation

status via IUCN

Least Concern

Wilson’s Warbler populations declined by nearly 2% per year between 1966 and 2015, resulting in a cumulative decline of 61% according to the North American Breeding Bird Survey. Populations in the West are declining at a greater rate than populations in the East. Despite these declines, they are not listed on the 2016 State of North America’s Birds Watch List, however the 2014 State of the Birds Report listed Wilson’s Warbler as a Common Bird in Steep Decline. Partners in Flight estimates a global breeding population of 60 million with 61% spending some part of the year in the U.S., 39% breeding in Canada, and 72% wintering in Mexico. The species rates 10 out of 20 on the Continental Concern Score. Primary threats include habitat loss on the breeding grounds, along migratory pathways, and on the wintering grounds. In some areas, Brown-headed Cowbirds pose a threat by laying their eggs in the nests of unsuspecting Wilson’s Warblers, a phenomenon known as brood parasitism. The warblers then raise the cowbird chicks at the expense of their own.

Credits

  • Ammon, E. M. and W. M. Gilbert. 1999. Wilson’s Warbler (Cardellina pusilla). The Birds of North America (P.G. Rodewald, Ed.). Cornell Lab of Ornithology, Ithaca, New York.
  • Karlson, K.T., and D. Rosselet. 2015. Birding by Impression: A Different Approach to Knowing and Identifying Birds. Houghton Mifflin Harcourt, New York, New York.
  • Mearn, B., and R. Mearns. 1992. Audubon to Xantus: The Lives of Those Commemorated in North American Bird Names. Academic Press, New York, New York.
  • North American Bird Conservation Initiative, U.S. Committee. 2014. State of the Birds 2014 Report. U.S. Department of Interior, Washington, DC.
  • North American Bird Conservation Initiative. 2016. The State of North America’s Birds 2016. Environment and Climate Change Canada: Ottawa, Ontario.
  • Partners in Flight. 2012. Species assessment database.
  • Ruegg, K.C., E.C. Anderson, K.L.Paxton, V. Apkenas, S. Lao, R.B. Siegel, D.F. Desante, F. Moore, and T.B. Smith. 2014. Mapping migration in a songbird using high-resolution genetic markers. Molecular Ecology 23:5726–5739.
  • Sauer, J.R., J.E. Hines, J.E. Fallon, K.L. Pardieck, D.J. Ziolkowski, Jr., and W.A. Link. 2016. The North American Breeding Bird Survey, Results and Analysis 1966–2015, Version 01.30.2015. USGS Patuxent Wildlife Research Center, Laurel, MD.
  • USGS Patuxent Wildlife Research Center. 2016. Longevity records of North American Birds.

Range Map Help

Wilson
View dynamic map of eBird sightings

Migration

Medium to long-distance migrant. Spends the nonbreeding season south of the United States from Mexico to Panama, but also winters along the southern coast of California and the Gulf Coast.

Backyard Tips

Wilson’s Warblers do not visit feeders, but you can provide habitat for them in your yard by landscaping with native trees and shrubs. Creating a bird-friendly backyard for Wilson’s Warblers even if they are not breeding in your area may help them out during migration. Head on over to Habitat Network to learn about which native species are good matches for your yard and more.

Find This Bird

Wilson’s Warblers breed mainly in the far north, so for many people they're easiest to find during migration. Spring can be the best time, as males often sing during migration. Look for them in shrubby tangles along streams or ponds or even forested edges and take a moment to listen for their rapid song. Unlike most warblers, they tend to forage at lower levels which makes finding them easier; no neck craning needed. The only real challenge is getting them in your binoculars. They don’t tend to stay still for long, so watch carefully and have your binoculars ready.

Get Involved

Read more about landscaping with native plants to give warblers a helping hand.

Learn about creating bird friendly backyards at Habitat Network.

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