I have a number of tit nest boxes on a wall about 5m from my kitchen. Two seem occupied by great tits. Today I saw a lesser spotted woodpecker putting his head into the one small nest hole. I suppose one should not interfere but my wife did tap on the window and it flew away.
I did look this up and apparently this nest robbing is not uncommon, but I had not realised it until now.
I've noticed recently, the odd magpie 'n' crow nickin' clumps of the stringy coir material from my hanging-baskets ... it's a win-win situation ... they get some nice bedding material and I get some really-really-wild-lookin' flower-basket-displays ;o)