The tree swallow (Tachycineta bicolor) is a migratorypasserine bird that breeds in North America and winters in Mexico, Central America and the Caribbean. It is a very rare vagrant to western Europe. This swallow averages 13.5 cm (5.3 in) long and weighs about 20 g (0.71 oz). The bill is tiny. The adult tree swallow has iridescent blue-green upperparts, white underparts, and a very slightly forked tail. The female usually has duller colours than the male, often more greenish than the more bluish male. The juvenile plumage is dull grey-brown above and may have hint of a grey breast band.