subspecies of the willow tit. It was promoted to species status based on a 2002 phylogenetic analysis that compared DNA sequences from the mitochondrial cytochrome-b gene. The single locus results were later confirmed by a larger multi-locus analysis published in 2017. Description The willow tit is in length, has a wingspan of and weighs around . It has a large head, a thin bill, a long dull black cap that descends to the and a black bib. The sides of the face are white, the back is grey-brown and the underparts are buff. The sexes are similar in appearance. In the east of its range it is much paler than marsh tit, but as one goes west the various races become increasingly similar, so much so that it was not recognised as a breeding bird in Great Britain until the end of the 19th century, despite being widespread. The willow tit is distinguished from the marsh tit by a sooty brown instead of a glossy blue black cap; the general colour is otherwise similar, though the under parts are more buff and the flanks distinctly more rufous; the pale buff edgings to the secondaries form a light patch on the closed wing. The feathers of the crown and the black bib under the bill are longer, but this is not an easily noticed character. The commonest call is a nasal , , , but the notes of the bird evidently vary considerably. Occasionally a double note, , , is repeated four or five times. Behaviour and ecology Breeding The willow tit excavates its own nesting hole, even piercing hard bark; this is usually in a rotten stump or in a tree, more or less decayed. Most nests are cups of felted material, such as fur, hair and wood chips, but feathers are sometimes used. The eggs are laid daily. The clutch is typically between six and nine eggs. The eggs have a white background and are marked with red-brown speckles and spots which are often concentrated at the broader end. They measure around and weigh . The eggs are incubated by the female alone and hatch after 13–15 days. The chicks are then cared for and fed by both parents but only the female broods the young. The nestlings fledge after 17–20 days. Only a single brood is raised each season. In a study using ring-recovery data carried out in