Blackbirds from continental Europe(particularly the north) do come here in the winter. I don't know what the weather has been like on the continent recently but perhaps these blackbirds are some of the winter visitors.
The only time I see the females is at a distance, they roost and nest in the very large Snowberry that surrounds our cess pit on the lower ground, where they do most of their feeding. The males however are always around the garden and back of the house, especially when they are feeding their young. I think the Mum's are lazy and leave it all up to Dad and end up looking thin and frazzled.
It is the first time I have seen a flock. They are still here this morning. They look slightly larger than my residents, but mine have had a pretty hard time of it with the weather.
The blackbirds here had a good year and at the end of the breeding season you could count a dozen plus out the front and more round the back, then they just disappeared a few are starting to show up again now and one female has taken up residents in a holly tree and eating her way through all the berries ian