Our garden blackbirds are nesting now and I often see the female collecting bits of stick and grass for the nest. The male tends to sit up in the bushes like this just keeping an eye on things.
There is nearly always a pair of blackbirds active around the house and it is easy to think they are the same ones every year but, in the 35 years we have been here, there must have been many generations - sic transit gloria mundi.
Blackbirds usually stay in or near the same place all the year round but some go on longer haul journeys. One famous bird travelled regularly some 228 miles from Norfolk to South Devon for the winter. See: http://news.bbc.co.uk/1/hi/england/4353671.stm