Why do I keep losing my Birthday Calendar. CanI retrieve it? This has happend twice now.
If you're speaking of the iOS included calendar app, the 'birthday calendar' it has comes from birthdates in your contacts. If the birthdates are still in your contacts but not showing up in the calendar app I'd try a reset--hold the on/off button and the home button down until the apple symbol appears in the middle of the display then release both and check again.
If you're speaking of some other birthday calendar I don't have an answer for you as I use the 'contacts' method.