I failed to find the collective noun for pied wagtails, so fell back on ‘dissimulation’ which is a generic term for a flock of small birds (deriving from their habit of diverting behaviour to distract predators).
I wanted to know because I came across a flock of wagtails in the berry-laden trees of Leigh Delamere services on the M4. It was dark, at about 5.40 pm and, as I walked through the car park, I heard a twittering in the small trees lining the roadways. They were faintly lit by artificial lighting.
Birds flew from one tree to another and then back again, perching in the branches. I had not seen such activity before. I hope the artificial lighting didn’t upset them too much.
I had a good look to see if there was a waxwing among them, but with no success.