Just to finish up the subject of motivating your employees...
We have all heard the phrase... The customer doesn't care how much you know until she knows how much you care.
Same can be said of your staff.
You should care how they are doing. You should ask what you can do to make their job better. You should know what is going on in their lives.
I was talking to someone whose boss did not acknowledge her when her father-in-law died. Do you think she's going to the mat for him? Would you?
Care for them and they will take care of your business.
PS At the very least you better celebrate their birthdays. Think about it like this. They are going to celebrate it with or without you. Better the former than the latter.