GGL calendar birthday events
[KB45081] Google Calendar can show birthdays and other events for any Google Contact that has a birthday or other event entered. To enable this feature in Google, simply subscribe to the Google Calendar called "Contacts' birthdays and events".
If you already have birthday events in your PC data, and have subscribed to this Google Calendar as well, you may see those birthdays listed twice in your Google Calendar. To prevent this, you can unsubscribe from the Google Calendar called "Contacts' birthdays and events", or hide the calendar from your view in the web browser.
If you are syncing a device to Google, these extra birthday events may appear on the device as well. Unsubscribing from that calendar, and then syncing the device with Google again, should clear them from the device.