Killing them was useless, according to Daniel Haag- Wackernagel, the scientist in charge of the anti-pigeon project in Basel. He found that mass extermination of adults only created room for juveniles to thrive.
He said a better approach was to breed colonies in lofts. The birds were healthier and control easier as eggs could be taken from the nest before hatching.
A four-year project has reduced the pigeon population by half, from about 1,400 in 1988 to nearly 700 in 1992, he said.
Previous attempts over 20 years using killing, sterilisation, and a ban on feeding failed, Dr Haag- Wackernagel writes in the science journal Nature. The city authorities also tackled the 'mental attitudes' of the pigeon-feeding public, emphasising how overcrowding caused the birds to suffer.
'We have found a satisfactory change in the mental attitude of the public,' Dr Haag- Wackernagel says. 'Feeding pigeons has become a taboo and only a few incorrigible people continue.'