A Burning Question

140807 Hummingbird Feeder

This is driving me a little crazy. The little yellow things on the ground normally cover the nectar holes on this hummingbird feeder.  I have three feeders around my yard.  Every day something has pulled these things off and they are lying on the ground as shown.  The feeder is about 3 feet off of the ground.  Any ideas what might be doing this?  Inquiring minds want to know.