Black-and-white warbler

Appearance

The black-and-white warbler is 11 cm to 13 cm in length with a mass of 8 g to 15 g grams.

True to their name, black-and-white warblers are black and white in colour. Both sexes have black and white crowns with a white eyebrow, black streaking on a white belly, black wings with two white wing bars, a black tail, a black-and-white streaked back, streaky undertail coverts, and grey-black legs and feet. Breeding males have a black-and-white streaked throat and black cheek, while females have a grey cheek and a white-cream coloured throat and sides. First fall males are very similar to adult females in colour and patterning, while first fall females resemble to adult females but with less streaking and a more noticeable buffy wash. Juveniles are heavily spotted, and are similar to first fall individuals otherwise.

This warbler can be confused with the blackpoll warbler. The blackpoll warbler is also black and white in its summer plumage, but has a solid black cap. The black-and-white warbler can also be confused behaviourally with the pine warbler and yellow-throated warbler.

Naming

The genus name comes from the Ancient Greek "mnion", meaning "seaweed", and "tillo", "to pluck". Vieillot mistranslated the first word, "mnion", as "moss". The specific "varia" is from the Latin "varius", meaning "variegated".

Distribution

The black-and-white warbler is a migratory species, breeding in North America and wintering in North and South America. It is typically found in deciduous forest in its breeding range, but becomes more of a habitat generalist in the non-breeding season.The black-and-white warbler breeds in northern and eastern North America. It ranges from the Northwest Territories to the northwest and Newfoundland and Labrador to the northeast, to North Carolina to the southeast and Texas to the southwest. This species is migratory, wintering in Florida, Central America, and northern South America down to Peru. The IUCN estimates the extent of occurrence, or range, to be 11 500 000 km2.

This species occurs as a vagrant in Iceland, Ireland, Faeroes, and the UK.

Status

The IUCN classifies the black-and-white warbler as Least Concern due to its large range and population size. However, its population is decreasing. Habitat loss and degradation, especially forest fragmentation, are the main factors contributing to the species’ decline. If habitat loss continues, in either or both summer or wintering habitat, the species may continue to decline in the future. Pesticides such as fenitrothion and phosphamidon have contributed to the species’ decline in the 1970s, and others such as chlorinated hydrocarbons may continue to have an effect.

Behavior

Its song is a high "see wee-see wee-see wee-see wee-see wee-see" or "weesa weesa weetee weetee weetee weet weet weet". It has two calls, a hard "tick" and a soft, thin "fsss".

Reproduction

The black-and-white warbler is of the first warblers to arrive to its spring breeding grounds. In the southernmost range of its breeding habitat, it can begin breeding mid-April. Males are territorial and defend their territory, both by singing and chasing competitors away. When a female arrives in a male's territory, he pursues her in an effort to breed. The male may display by flapping his wings.

The nest is cup-shaped, often located on the ground among roots or against a tree, or in crevices on tree stumps. The species prefers to nest in damp areas. The nest is constructed with grassy material, bark, and dry leaves, and lined with softer material such as moss and hair. The female is responsible for most of the nest-building. The female lays 4-5 eggs, which are light brown and speckled with darker brown. The female begins incubating once the last or second-to-last egg is laid. Incubation lasts 10 to 12 days, and is done solely by the female. During incubation, the female is sometimes fed by the male.

Both parents care for the nestlings. The young fledge after 8 to 12 days, and stay around the nest while they improve their flight ability. During this time, the parents remain nearby.

This species generally produces one brood per year.

Black-and-white warbler nests are sometimes parasitized by the brown-headed cowbird.

Food

The black-and-white warbler feeds in a manner similar to a nuthatch or a creeper. It forages on tree trunks and limbs to feed on insects below the bark’s surface. Its short legs and long hind toe are adaptations to this foraging method. The black-and-white warbler is unique among warblers in its time spent foraging on tree trunks and inner branches. This bird also gleans, like many warblers, for insects. Its diet is composed of insects and other arthropods, including lepidopteran larvae, beetles, ants, and spiders. During migration and breeding, this warbler relies heavily on lepidopteran larvae.

During migration, the black-and-white warbler sometimes joins mixed flocks to feed.