When you import contacts, their birthdays are not automatically added to the calendar as they are when you create a new contact manually or edit existing contacts.
You have three options:
1. Open and save each contact
2. Use VBA code (http://www.outlookcode.com/d/code/remindbday.htm)
3. Use a utility: Put Anniversary in Calendar (http://www.rsoutlook.com/us/prods/prod05.html)
From Adding Birthdays and Anniversaries to the Calendar http://www.slipstick.com/contacts/addbirthdays.asp
