The most common species of wild bird worldwide is the rock dove, known by most people as the "pigeon." It is estimated that pigeon populations number over 400 million worldwide.
The rock dove was originally a wild bird species that inhabited seaside areas with high cliffs. People domesticated the species, using it for food and also as carrier pigeons, taking their pigeons with them on journeys across the globe. When pigeons were taken overseas, some escaped or were released by their owners, leading to large feral pigeon populations in many cities around the world. Feral pigeons have adapted to living in cityscapes because of the similarity between the large buildings and the sea cliffs that they are naturally accustomed to.