Repeated birthday events in laptop Calendar, conflicting with iPhone and iPad

When I opened the Calendar app on my laptop today, I saw the same 5 events repeated every single day (mostly birthdays).

The Calendar apps on my iPhone and iPad are 'normal' and I have NO idea what could have populated these same birthday events onto my laptop calendar.

And it's not just the current month. I scrolled back to 2012 and ALL of those events are listed every single day.

I'm afraid to try to sync my iPhone with my laptop since I have no idea WHICH device's information would dominate and I don't want to screw up the calendars on my mobile devices.

Thoughts?

[Re-Titled by Moderator]

Original Title: Calendar Has Gone Kookoo