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 Google, 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?

If I look at the Calendar app on my Mac (which is running Yosemite), I don't see all of these calendars. I only see one under Google that says "Birthdays", another under Google that says "Friends' Birthdays", and one under Other that says "Birthdays".