Urbanisation of the wood pigeon (Columba palumbus) in Finland

• Wood pigeons have been breeding regularly in Finnish cities since 1991; the urbanisation process is still in progress.
• Larger cities and cities located closer to the sea were colonised first.
• Colonisation did not follow the stepping-stone model between nearest neighbouring cities.
• Changes in rural wood pigeon density did not drive the urbanisation process.
• Habitat use of wood pigeons changed during the urbanisation process.

The urbanisation process includes three phases: arrival, adjustment and spread. While these are much studied for biological invasions, stage-specific factors promoting successful urbanisation are still poorly understood. In this paper, we study urbanisation of the wood pigeon, Columba palumbus, in Finland. We document the colonisation of the 20 largest Finnish cities; studying how size of the city, geographic location, population density in rural areas surrounding a city, and distance to other previously colonised cities influenced the timing of arrival. We also investigate population development and changes in habitat use during the adjustment and spread stages of the urbanisation process in the city of Turku. We obtained data on wood pigeon observations in inner-city areas from the database of BirdLife Finland, public questionnaires and systematic searches. We found that larger cities and cities located closer to the sea were colonised earlier. Colonisation seemed to be unrelated to both density of rural wood pigeon population and distance to the nearest colonised city. The settlement and spread phases of the urbanisation process followed an exponential curve. No preference for coniferous forest, the habitat type used in rural areas, or deciduous forest was observed. Nests were mainly located in deciduous patches, which are common in cities. We conclude that colonisation of cities by wood pigeons was influenced by geographic location. The hypothesis that avian urbanisation follows the stepping-stone model between neighbouring cities was not supported. Additionally, our results confirm the hypothesis that, during urbanisation, habitat use of species changes from that in rural areas.