Robins frequently feature on Christmas cards and often on Christmas stamps. In 2001 the Royal Mail issued this set, here as the PHQ stamp cards.
Robins have been associated with Christmas in the UK ever since the mid 1800s. Postmen used to have a red uniform (in fact they still do to some extent) and became known as robins. The robins on Christmas cards symbolised the postmen delivering the mail until they became associated with Christmas in their own right. I'd be interested to know if other countries also associate robins with Christmas. I know you have different birds called robins in north America.
This is a post for Sunday Stamps, now hosted by Violet Sky at "See it on a Postcard!"