By accident I deleted the iCloud Birthdays Calender (Filled with birthdays of my contacts) from the iCloud Calender (left side in the list).
Does somebody know how to repair this?
Go to icloud.com from a computer, sign into your iCloud account, open Calendar, click on the Actions (gear shaped) icon on the upper right and choose Preferences. On the General tab check "Show Birthdays calendar" and click Save at the bottom.
Retrieving data ...