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Black-and-white Warbler

Mniotilta varia ORDER: PASSERIFORMES FAMILY: PARULIDAE

IUCN Conservation Status: Least Concern

One of the earliest-arriving migrant warblers, the Black-and-white Warbler’s thin, squeaky song is one of the first signs that spring birding has sprung. This crisply striped bundle of black and white feathers creeps along tree trunks and branches like a nimble nuthatch, probing the bark for insects with its slightly downcurved bill. Though you typically see these birds only in trees, they build their little cup-shaped nests in the leaf litter of forests across central and eastern North America.

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At a GlanceHelp

Measurements
Both Sexes
Length
4.3–5.1 in
11–13 cm
Wingspan
7.1–8.7 in
18–22 cm
Weight
0.3–0.5 oz
8–15 g
Relative Size
About the size of a Black-capped Chickadee; slightly smaller than a White-breasted Nuthatch.
Other Names
  • Paruline noir et blanc; Fauvette noire et blanche (French)
  • Chipe trepador; Reinita trepadora; Verdin trepadora; Mezelilla (Spanish)

Cool Facts

  • The Black-and-white Warbler is the only member of the genus Mniotilta. The genus name means “moss-plucking,” a reference to its habit of probing bark and moss for insects.
  • Black-and-white Warblers have an extra-long hind claw and heavier legs than other wood-warblers, which help them hold onto and move around on bark.
  • As warblers go, Black-and-white Warblers are combative: they’ll attack and fight with other species that enter their territory, including Black-capped Chickadees, Red-breasted Nuthatches, and American Redstarts. This aggressive behavior extends to the wintering grounds, where they defend territories and when feeding in mixed flocks will drive other Black-and-white Warblers away.
  • The oldest known Black-and-white Warbler was 11 years, 3 months old—a female that was banded in North Carolina in the 1950s and recovered in Pennsylvania more than a decade later.

Habitat


Forest

Black-and-white Warblers typically use deciduous forests and mixed forests of deciduous trees and conifers. They can be found in many habitats during migration, especially woodlots and forests in riparian settings. On their tropical wintering grounds Black-and-white Warblers use an immense range of habitats, including lawns, gardens, and other urban settings, fruit orchards, shade-coffee plantations, wetlands, mangroves, and all types of forests.

Food


Insects

Black-and-white Warblers eat mostly insects. Moth and butterfly larvae form the bulk of their diet during spring migration and throughout the breeding season. Other arthropod prey includes ants, flies, spiders, click and leaf beetles, wood-borers, leafhoppers, and weevils. They also feed on insects attracted to Yellow-Bellied Sapsucker sapwells.

Nesting

Nesting Facts
Clutch Size
4–6 eggs
Number of Broods
1-2 broods
Egg Length
0.6–0.7 in
1.5–1.9 cm
Egg Width
0.5–0.6 in
1.3–1.4 cm
Incubation Period
10–12 days
Nestling Period
8–12 days
Egg Description
Creamy white, pale bluish- or greenish-white, with speckles of brown or lavender.
Condition at Hatching
Helpless, with pink skin and dark gray down.
Nest Description

The round, open cup-shaped nest is constructed from dry leaves, bark strips, grass, and pine needles, reaching just over 5 inches in diameter and 5 inches high. The nest cup, which measures up to 3 inches in diameter and 2.5 inches high, is lined with moss, horsehair, and dried grasses.

Nest Placement

Ground

The female Black-and-white Warbler selects a well-hidden nesting location at the base of a tree, rock, stump, or fallen log, or under a bush or shrub. Nests are usually built on the ground but occasionally are placed in a cavity atop a tree stump, in a rock crevice, or on a mossy bank up to six feet high.

Behavior


Bark Forager

Black-and-white Warblers crawl along tree trunks and thick limbs as they probe methodically between bark fibers for grubs and insects. Unlike Brown Creepers, which tend to move up a tree as they feed, or nuthatches, which typically move downward, this warbler moves in every direction. They forage on dead limbs and bark as well as gleaning foliage at the tips of branches. Male Black-and-white Warblers arrive in early spring on their forested breeding grounds and set up territories that they defend aggressively, often singing as they chase off intruders. These defensive displays extend well past the time when such behavior has tapered off for other species. A courting male chases potential mates on his territory, perching nearby and fluttering his wings. Once the pair is established, the female leads her partner to likely nest spots at the base of a tree or fallen log, and takes the lead in constructing the well-camouflaged nest.

Conservation

status via IUCN

Least Concern

Black-and-white Warblers are common, although populations in the U.S. have been on a gradual decline (estimated at 0.9 percent per year) in the last half-century, according to the North American Breeding Bird Survey. Partners in Flight estimates the global breeding population at 20 million, with 25 percent breeding in Canada, 75 percent spending some part of the year in the U.S., and 43 percent wintering in Mexico. It rates a 10 out of 20 on the Continental Concern Score and is not on the 2012 Watch List. In the past, Black-and-white Warblers have proven susceptible to persistent organic pesticides used to combat insects. Today, the main concern for this forest-interior species is fragmentation of forests into smaller and smaller parcels. Like many nocturnal migrants, Black-and-white Warblers are vulnerable to collisions with tall buildings and radio towers.

Credits

Range Map Help

Black-and-white Warbler Range Map
View dynamic map of eBird sightings

Migration

Short- to long-distance migrant. Some individuals winter as far north as Florida and Baja California; others go as far as northern South America. This is typically one of the earliest spring arrivals among Neotropical migrants.

Find This Bird

Black-and-white Warblers are fairly common and often intent on foraging along tree limbs, so they don’t tend to be shy. Watch for them creeping fairly rapidly on, around, and under larger branches of taller trees. Black-and-white Warblers are also quite vocal. Their song is thin, almost squeaky, but penetrating, so it’s a good way to find them. Watch for them during migration (especially early in the season): at least one or two are typically found in any reasonably good arrival of migrant warblers.

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