Northern Prairie Wildlife Research Center
At the Llandegfedd reservoir in the Usk Valley, where the fishing season has recently been advanced by 2 weeks to 20 March, anglers choose parts of the reservoir which birds such as Eurasian wigeon (Anas penelope) and green-winged teal (Anas crecca) also prefer. The reservoir is an important trout fishery, but it also supports the highest number of overwintering waterfowl in South Wales. As a result of the anglers' intrusion, these birds gathered in the center of the reservoir during the day, away from the shallow areas and shore where they would normally feed on grasses and herbs. Birds dispersed from the site after a few days, possibly because of increased sailing activity in central areas. The number of Eurasian wigeon, for example, fell from over 400 to about 60 within a week. This contrasted with a much more gradual emigration from a nearby, undisturbed site at Slimbridge on the Severn Estuary.