 The reservoirs are also one of the capital's main roosting site for gulls; 70,000 of these have been recorded at one time, the majority being black-headed gulls, common gulls, lesser black-backed gulls and herring gulls.Since the 1950s, the reservoirs have been providing a refuge for wildfowl while they are vulnerable during the late summer moult, and in some years, moulting flocks of great crested grebe have also used the reservoirs as a refuge.The reservoirs have also been used by migratory birds as a stopover site in autumn and spring, and yellow wagtail regularly breed here.