They do it in January because then you know how many have got through the winter, and they have not started nesting yet.
Last year there was thick snow on the ground, so they needed to come to the birdfeeders. This year the weather was a lot milder, but windy, so they could stay in the woods.
I always have one or both of the grandchildren that live round the corner. This year it was my grandson, 11, autistic, so to get him to sit still for about an hour is a feat in itself. We sit on my bed and look out of the window, with birdbooks for him to go through and binoculars so he can try and count the feathers on a sparrow. Yesterday we had a discussion about what bird a vegetarian would want to come back as. Obviously he was thinking about Grandad, who would not want to be a blackbird as he would have to eat worms. We decided that Grandad could be a goldfinch, and grandson could be a greenfinch as that's his favourite colour. Even though grandson eats fish, he would not want to kill them, so could not be a kingfisher or osprey, not that we get that many of those in our garden!
It's amazing how much information you can get into your grandson's head in an hour. He could have forgotten about it today, but he does have the sort of memory to remember facts. He just does not know what to do with them when they are in his memory.