Sync birthdays between iCal and Android
Okay, I am admittedly not an Apple guy, but it looks like you might need a third-party solution.

According to some comments I found here, non-support of birthdays is a known thorn. To get around it, the commenter used Spanning Sync but also mentioned SyncMan.

Spanning Sync offers a 15-day trial, after which it costs $25 for a one-year subscription or a $65 one-time purchase. The commenter referenced above did mention that he chose this because birthdays were not being sync'd.

SyncMan offers a 30-day trial, after which you can purchase it for $14.99. On the support page it specifically mentions birthdays as one of the things it syncs that the native Google sync in Address Book doesn't.