Winter visitor and passage migrant. Not recorded in June or August
Mathew (1894) assessed the Brent Goose as being a "sometimes abundant" winter visitor, that arrived between 29 September and 7 October. Brent Goose populations declined during the 1930s when their winter food plant eelgrass (Zostera marina) was decimated by disease. However, whilst on the breeding grounds they also suffered from predation by humans, which could have been a more significant reason for the decline at that time.
Following the cessation of persecution in the late 1950s the population increased and has also shown an adaptability in food choice that suggests the decline in eelgrass may not have been so critical as previously thought. By 1949 they had become an irregular visitor to Pembrokeshire. Lockley et al. (1949) noted that the subspecies occurring had not been identified. Lockley (1961) later stated that the Brent Goose was a regular visitor to the south-west peninsula of Pembrokeshire, "chiefly to Angle Bay". Up to nine still appear there in winter sometimes, and these are mainly Dark-breasted Brent Geese, subspecies bernicla. Winter occurrences elsewhere are infrequent.
The severe winter weather of 1963 saw a group of 22 Dark-breasted Brent Geese take refuge at the Gann, with another nine appearing on Manorbier beach in the freeze up of 1987. In both cases they were presumably birds displaced from further east.
Between September and December, parties of up to 39 birds on autumn passage are a regular feature, moving through coastal districts. There is a less regular and smaller spring passage, of fewer groups of up to 22 birds, in April and May. Dark-breasted Brent Geese occur, but the majority seen moving are Light-breasted Brent Geese subspecies hrota. The largest group seen to date was 48 passing through Jack Sound on 8 October 1949.
A single Dark-breasted Brent Goose was at the Gann on 17 July 1988.