Who doesn't like receiving some cash on their birthday?!?!
Set up birthday awards in the Milestones section of Setup. When you set up a birthday award, then the employee's will automatically get the bonus amount put in their spending balance when their birthday post is posted to the feed. You can set up birthday awards so that employee's either receive cash or a local reward item. The screenshot below shows that every user is going to get $15 in their spend balance on their birthday.