A couple of weeks ago I spotted a pair of grey wagtails (Motacilla cinerea) feeding at Bottisham Lock on the river Cam at Waterbeach, a few miles north of Cambridge. I was rather pleased to have snapped them in the evening sun. Several weeks later I saw the female foraging a few hundred metres further down river at the pumping station that helps control the flow of water along the lode there to the village of Bottisham itself. She was flitting about on the accumulated debris at the smaller lock on to the lode where river plants and detritus at accumulated, snatching at invertebrates, flies, mayflies, beetles, crustacea, and molluscs. The male will also assist in caring for chicks, although I didn’t see him on this expedition. Interestingly, the female may also lay a second clutch, leaving the male to look after the first brood.
Presumably she has chicks to feed now and was hurriedly stuffing her beak ready to head back to her nest. The species always nests among stones and roots on the embankment of moving water, rivers, streams, but might also exploit man-made structures too, such as locks and canals.