Not to put a damper on the thread, but it is not wise to use Vaseline, Pam or any other grease where birds can come in contact with it. It will reduce the waterproofing an insulating qualities of their oiled feathers which could kill them.

Today one of my fat gray squirrels got hung up on one of the feeders and paniced as I approached the feeder. In desperation it jumped for the fence 15+ feet away missing its mark only to crash land on a thorn bush.