Grey Wagtail This bird is present all year round but returns to its' nest site in late March. Some birds will leave in the Autumn heading for the lowlands. They breed on watercourses that have a good supply of aquatic and non-aquatic insects i.e. most of the streams around the Vyrnwy area. In 1998, 14 pairs of grey wagtail were seen to be breeding around the Lake shore and streams across the reserve. This species is a good indicator of water quality, as it's food source would not be present in areas of poor water quality.