A flock of feral pigeons is circling above downtown Frankfurt. The city hosts about 5000 of those birds that can become a plague in some places. Men created this problem centuries ago. He domesticated feral rock pigeons and made them breeding machines who breed up to eight times a year instead of two times like their ancestors did. But domestication did not rob pigeons of their need to breed in rock, or similar environments, so feral pigeons came to live in cities and buildings, also because they forgot how to survive in the wild.