Why Do You Have To Pay A Speacal Tithe On Your Birth Day?

I've been going to an Episcopal Church and if it's someone's birth day then they make that person pay a speacal tithe while standing in front of the congregation. They bring out a piggy bank for them to put money into. Why does someone have to pay a speacal tithe on their birth day? I think that would be really embaring if it was my birth day and I didn't have any money on me or if I didn't have my purse.