These are Chinese geese, I think, a breed of domestic goose, but they have escaped from whoever owned them and have taken to hanging out with a large flock of Mute swans that live on the banks of the River Taff in central Cardiff. People regularly feed the birds in this area, so the geese and swans are joined by Mallards, big groups of Feral pigeons and scavenging gulls.

Apparently, Chinese geese have been domesticated for their eggs and their meat, and the knob above their beaks is larger in ganders, so the white goose must be a male and the three brown birds females.