All prepared and can't wait!

I work 8 to 5 during the week so I do not get a chance to see what is actually eating all the goodies that I am putting out. I normally refill all the feeders on a Saturday, but this week, I have been topping up my bird feeders and ground feeders in preparation for the BGBW when I get in (in the dark).  The ground fedeers have been completly emptied everday so I can't wait for tomorrow to actually see what is eating all the tasty morsels I have been tempting them with. The favourites of which are meal worms and sun flower hearts covered in beef suet.  I have a feeling that it maybe a pair of rather greedy Magpies!

Just out of curiosity, can anyone tell me why the BGBW takes place in January?