There are 30 records of Yellow-rumped Warbler, with the only form confirmed as occurring in the UK (and indeed Europe) being Myrtle Warbler. However, of these many have occurred on off islands with Cape Clear and the Isles of Scilly accounting for half of the records to date.
The cracking photograph below taken by Martyn Sidwell shows many of the distinctive features of this species, including a hint of the yellow rump and breast breast side which distinguish it from all similar species.
There are two 'groups' of Yellow-rumped Warbler, Audobon's Warbler breeds within the south-western USA while Myrtle Warbler is the northern equivalent. Within Audobon's there are three races while the Myrtle group contains two races. These two groups were once split but are now generally considered to represent a single species, with Audobon's being a short distance migrant or sedentary (depending on race) while the Myrtle is a long distance migrant and hence more prone to vagrancy Male and female Audobon's are readily distinguished from Myrtle by their bright yellow throats which in Myrtle is off white to white. However, first winter birds such as that at High Shincliffe are more subtle with Myrtle having a more extensive pale throat wrapping around the ear coverts (as can be seen in the above photograph) and a more heavily streaked breast.