I had not seen Yellow Wagtails at all until a local birdwatcher told me that there were some along the cliff "in the field with the cows".
I duly took a walk to the designated field and there were indeed cows in it. Only then did I realise exactly what my informant had meant - the birds were very much "with the cows" as the picture below shows.
The picture above left illustrates the colour variation between the sexes. All pictures will enlarge slightly.