I think the amount of snow we had on saturday contributed to the vast amount and variety of birds we had visiting on our birdwatch. As we cleared the snow from our bird tables and feeders to put food out, the birds were there watching and a collared dove almost landed on Grans head as she was on her way in, in its rush to get to the food. And our neighbourhood squirrel visiting didnot put the birds off.
At one point the birds were litterally queing on the garden fence and garage roof for their turn (including 2 wood pigeons, a black bird on the fence, and a magpie and 4 pigeons on the garage) at a pot of peanuts
When the snow is on the ground, it covers up or certainly makes it trickier for birds to find their usual food stuffs. Thats why the food we put out during these cold snaps is all the more important. Glad you enjoyed your birdwatch, sounds like the birds did too!