While many Dunnocks remain solitary through the winter period if you feed regularly and have several feeders it is possible to attract small gatherings, I have counted at least 10 feeding around my garden, almost always spread out in small groups of two-three around the hedges and shrubs of the borders.
By the time we start to head past Christmas males will begin to find their voices ahead of next Spring and their clear, strong 2-3 second song bursts will ring out again. Listen out for a song that always seem to be a little hurried, repeated often. They frequently sit atop a conifer or bush to sing so can be fairly easy to pick out, dull, grey/brown with pinkish legs and a thin bill.
Often during early Spring Dunnocks appear in threes, two males and a female. The devilish female Dunnocks encourage both males to mate with low posture and fluffed feathers. There is method in the apparent madness of this love triangle and it is to the benefit of the female with opportunities to mate with both males and ensure that she is provided with sufficient food during the breeding period.