I knew there was at least one of these (Motacilla cinerea) at the park, because it's often reported there - and I caught a glimpse, just once, a couple of years ago. But I never see it when I go, so this was a bit of a surprise encounter.
I only noticed it because a pied wagtail - which are far more numerous - kept harassing it. It fed, largely unnoticed, along the edge of the lake, very close to passers by. Eternally active, so most shots were duds, but I only needed one to work out. This is by far the closest I've ever got to this species - I see them in Scotland regularly, but they are very skittish.
Note this is a winter-plumage bird - it would have even more yellow on its breast in the breeding season.
Explore 20-02-14 - thanks everyone!
Canon EOS 5D mark III, Canon EF 500mm f/4L IS II USM, Canon EF Extender 2x II (handheld).
1000mm, f/10, 1/1000, ISO 800.