Why Robins at Christmas

We associate robins with Christmas, the bird that always appears on Christmas cards. Why a Robin?
I beleive it is because the Robin is most visible at Christmas, when its bright red breast is easily seen against the stark white snow.
It sings all year round and so provides a welcome cheery sound in the depths of winter. It is however a fiercely territorial bird and if any other birds make the mistake of tresspassing onto his territory even if it is do the birdy equivalent of carol signing then it will get short shrift from the fiery little character.

Here is my version, sadly not as cute as it ought to be.