Young Pied Wagtail

Today a rare visitor to the garden, the first one I have seen here in fact, a wagtail I thought was a grey one but it is an immature pied wagtail (should have checked the Macmillan bird book before posting the first entry!).
Unfortunately I had to take this one through the window as it would have flown off immediately if I had opened said window. It was hunting around and finding nothing on the ground, pity it did not go to the bird table less than a metre away, which is full of food at the moment, but I believe wagtails prefer worms and grubs to nuts and seeds.