Ridiculous number of unnecessary birthday calendars that can't be deleted

I have an iPhone 5 running iOS 8.1.1. My Calendar app is showing me a ridiculous number of birthday calendars ("Friends' Birthdays" under Gmail, "Birthdays" under Facebook, and 8 separate calendars named "Birthdays" under "Other"). This is what the list of calendars looks like:

I have no idea how they got there. I am syncing the Calendar app with Gmail, Facebook, and Meetup, but I can't imagine how that would produce such a ridiculous number.

What can I do about these? I would like to delete or merge some of them but the app is not giving me the option. Is it possible to delete most of them without losing anyone's birthday?