That is true. It may be so strenuous to give all of them bonuses during their birthdays. Why don't you go for something simple like gift cards? Anyway, it will depend on the capability of the company. Some are big enough to give such bonuses.Given bonuses on employees birthdays is very stressful personally I think simply because if you are having more than 30 employees, how will you satisfy them when having birthdays at a specific time.