I have entered the birthday for several of my Contacts, and these birthdays show up in Calendar. I know that I can enable or disable all birthdays by selecting or deslecting "Birthdays" from Show Calendars in the top corner of the Calendar app. But I only want to see some of my contact's birthdays in the Calendar; for example, personal contacts but not ex-coworkers.
How can I prevent the display of certain birthdays?
As a compromise, you can disable the notification for that person's birthday. In calendar, double click on the birthday even and then change the alert to none. You will then be prompted if you want to change this event or all future events. Select all future events and you will no longer receive notifications for that birthday. It will however remain in your birthday calendar, but you will no longer be pestered with reminders (which is what I came her looking for before figuring out I could disable the reminder)
This script iterates over your contacts. For each contact, it will delete the contact that has the birthdays
tell application "Contacts"
set peopleToChange to people whose (birth date) is not missing value
repeat with thePerson in peopleToChange
delete ((birth date) of thePerson)