Feral pigeons are often found in urban public spaces. They are often considered environmental pests, and can transmit diseases such as psittacosis. Deliberate feeding of feral pigeons, though popular, contributes to these problems.
Ducks are also commonly fed in public spaces. In one US study, 67% of people visiting urban parks did so to feed ducks. However, such feeding may contribute to water pollution and to over-population of the birds, as well as delaying winter migration to an extent that may be dangerous for the birds. Feeding foods such as white bread to ducks and geese can result in bone deformities.