The Yellow-rumped Warbler, (Setophaga coronata), or "Butter Butt" as it is affectionally known, has two common subspecies in the US – Audubon’s and Myrtle. There are four subspecies in total – with the Black-fronted and Goldman’s Warbler confined to Mexico and Central America. The Myrtle or Taiga subspecies is very widespread, breeding in the boreal forests from Alaska to the Atlantic and wintering across the Southern US and into Mexico and Central America but is more numerous in the East. The Audubon’s subspecies is restricted to the Western half of the US breeding from British Colombia to California and wintering in the west of Mexico and Central America. Note that these subspecies were considered as separate species until 1973 and some authorities still consider them as such.
A common and typically easily seen warbler, they nest in coniferous forests and edges. In Winter, their habitats are much more widespread from scrub to woodland to gardens etc. Both sub-species can be found in Texas during migration and in Winter, but Audubon’s are typically restricted to West Texas.
The Yellow-rumped Warbler typically nests in Conifers, usually above heights of 10 feet. Its nest is quite bulky and is constructed of roots, twigs and grass in which 3-5 creamy white eggs streaked gray and brown are laid. Incubation lasts 13 days and is exclusively carried out by the female.
Typically, these warblers feed on insects in the summer and also feed them to their young, but are very adaptable and more readily eat fruit and berries in the Winter
The song of the Yellow-rumped Warbler is variable but is a musical warble. Its call is a soft “chek”.
Both sub-species are gray above streaked with black and dark wings with 2 white wing bars. They have a dark tail with white at the corners and, as the name implies, a bright yellow rump. Both have a yellow crown patch and a dark to black mask with yellow flanks and white underparts with some dark streaking. The two sub-species are markedly different as the Audubon’s has a yellow neck and throat, while the Myrtles’ is white. In Winter, both sub-species are much more drab with a mid-gray brown breast, back and head. Both are streaked but the Myrtle much more heavily. Both retain the yellow flanks and rump. Both have a pale throat but the Myrtles' is much more extensive with the pale area wrapping round to the auriculars. Both have white eye arcs in all plumages.
• A group of warblers have many collective names including a bouquet, a fall, a confusion and a wrench.
• Yellow-rumped warblers have a very high tolerance to wax-coated berries. This allows them to Winter much further North than all comparable species.
• Recent genetic testing suggest it is likely that this species will be split again into 2 separate species. The Myrtle sub-species was separated by glaciation in the last ice age. The Aubudon’s appears to have originated as a hybrid between Myrtle and the central American Black Fronted sub-species.
• Yellow-rumped males forage higher in trees than females and both will drive off other competing species.
• While a solitary nester, Yellow-rumps often form foraging flocks in Winter and often do so with other species.
• This species was first described by Linnaeus in 1766.