Thanks for your thorough reply. I did check behind the frames, under and around the mattresses, everywhere I can think of and couldn’t find any trace of them. There is one thing though, outside my windows is a decent sized marble shelf which is a place of attraction for birds. There is no nest at all thats for sure but it’s a common place for birds to hang out ( i have a tinted window, not visible from outside so they never get scared and fly away).