Blue-headed Wagtail Motacilla flava flava
Very scarce passage migrant, mainly spring. Has bred sporadically.
This race breeds in north-western Europe. Lorand and Atkin (1989) described it as a sporadic breeder in the 1970s and stated that it had bred at Donna Nook, Covenham Reservoir, Cadney and Goxhill. There were no breeding records in the Atlas period during the 1980s or the BTO Atlas 2007-2011 or since. In the five years to 2018, LBR reports a total of 21 records all in April-May ranging from none in 2018 to 12 in 2015 with one in 2015, three in 2014 and five in 2016. In the same period there were four reports of “Channel Wagtails” (see last paragraph), hybrids between this race and the local flavissima British race. There were two in 2016 and a single in 2017. Interestingly a Channel Wagtail paired with a Western Yellow Wagtail bred at Marston STW in 2014. Identification of this race can be challenging given the tendency to hybridise and observers are encouraged to submit photographs wherever possible.
In northern France, there is an 'intergrade zone' where Blue-headed and Yellow Wagtails regularly interbreed, these intergrades are colloquially known as 'Channel Wagtail'. This hybridisation probably also occurs most years in the UK. The offspring of such pairings are variable in appearance, but many individuals show a head pattern that resembles a washed-out Blue-headed, with a paler powder-blue head and often more extensive white in the supercilium, ear-coverts and throat. They are the commonest form of Blue-headed to occur in many northern areas of Britain.
Reference
Tilmouth, A. (2010). Focus on: shades of Yellow Wagtail. In Bird Guides April 28th 2010 https://www.birdguides.com/articles/species-profiles/focus-on-shades-of-yellow-wagtail/ accessed December 2022.
(Account as per new Birds of Lincolnshire (2021), included December 2022)