We have found several dead birds in and around our farm since the really cold nights have started. Most of them are young birds and I think they have failed to work out where the warmer parts of the farm are - The cowsheds are one of the most popular roosting sites.
]Birds lose so much weight overnight that a good breakfast can really help survival rates. Currently I am feeding Wiggly Seed Extra, British Mix, Huskless, Niger and Mealworms. My approach is there's lots of tiny seeds in there to appeal to small birds (hemp, linseed etc), you can't go wrong with sunflowers and sunflower hearts, and mealworms are the equivalent of chocolate to me (and they contain water which really helps when everywhere is frozen solid).