How to delete all birthdays that show up in iCalendar

I need help with deleting all the birthdays that appear in my iCalendar on my computer, which are coming from my Gmail contacts. While my iPhone's iCalendar looks fine, my computer's iCalendar is cluttered with birthdays of every person I've ever had in my contacts. I recently synced my contacts and calendars to avoid double entering appointments and finding contacts, but this has created a mess. How can I remove those birthdays from my computer's iCalendar?