Welcome to Android Central! There's usually a separate Birthdays calendar. Look at your list of Calendars, and if you see one called Birthdays, uncheck it or toggle it off so that it doesn't display.
If your phone is somehow syncing Facebook contacts with the main Contacts app (which would be odd, since Facebook took that feature away a couple of years ago), then try going to Settings>Accounts>Facebook, and see if there's a checkbox for Contacts. If so, uncheck it there.