Common Pigeons (Columba livia) and their feral domestic relatives nest in a variety of sites, but use of nests of other birds has not been reported. I documented 13 nesting attempts by feral Common Pigeons in seven large compound nests of Monk Parakeets (Myiopsitta monachus) in Cordoba, Argentina; at least three attempts produced nestling pigeons. The parakeets did not directly attack the pigeons, but either made an entrance tunnel or completely blocked the chamber entrances with thorny sticks where pigeons nested, eliminating access to chambers and causing the pigeons to abandon their nests.