added birthdays & anniversaries???

I synced my contacts a long time ago between my office (Lotus notes) and Contacts. They contained some birthdays for my family and close friends. Now ALL contacts (thousands) have shown birthdays and anniveraries invented by .....don't know....mostly in year 6771. So --- any way to edit birthdays out of most? I can't spend the time to individually edit over 3,000 entries. Is there a way to only show certain birthdays rather than all or a 'mass edit' where I can delete most birthdays and anniversaries and then just re-enter those I want? Thanks