You fed it?
Big mistake. Unless you catch it and ring the owner you now have a pest for life.
At our old house, we found a racing pidgeon, managed to catch it, kept it overnight in a box (with holes and food etc) and the owner came the next day to pick it up. No problem.
Recently (within the last year) another pidgeon landed in our house, looking tired and mopey etc etc. So we gave him food - but couldn't catch him. He hung around for a week, pestering us at open windows and that. It was cute....but began to get annoying. Eventually we caught him, rung the owner who told us to release him a distance away from our house, and it would fly to him. So pidgey was taken to the middle of the southdowns and released. Sorted.
Or not. Two days later, my parents were in the study and heard a "pitter patter pitter patter", turned round and were greeted by pidgey who had come in through the open door in our conservatory, through our kitchen, through the hallway into the study. After this, the owner agreed to come collect said bird.
Now, the worst bird incident, one which still pisses me off on a daily basis.
The Doves.
A few roads away a family used to keep many doves in a dove cotte - about 20 or so. About a year ago, they knocked this cotte down, because the doves were annoying them. Shame there has been no action taken on this as these doves are very domesticated. Anyway, the number of doves soon reduced, and now there are a pair of them who kept hanging around our house. Feeling generous, one of us in the family of 4 fed them. The doves grew more and more clingy, coming to open windows and making the most annoying noise. It was still funny, and cute to have these beautiful white birds around. The my dad, thinking he was a funny fcker put bird seed on my windowsills without me knowing. He did this reguarly and now the doves will not piss off. I have found them inside the house a few times, but the most annoying this is that every morning, they come to my windows (which I leave open to sleep) and make the most annoying noise you could imagine. If I am asleep or not there, they will come inside my room. I always scare them away but they come back after less than a minute - not always back to the same window (I have 3). They will do this for up to 20 minutes, one window, then another, then another, making the terrible noise. At 4am this can be infuriating.
If I ever catch one of them, it is dead. I will feel no remorse, no guilt. It will die.