New species still arriving in our cities

Species that want to survive in settlements face a host of challenges. Besides distinct habitat features, a different species composition (e.g. new competitors or predators, many non-native plants) and a range of hazards (e.g. traffic, glass windows), the direct and indirect disturbance caused by the permanent presence of humans is a particular challenge. Birds also need to adapt to noise and artificial light. The colonisation of towns can occur independently in several locations (e.g. Eurasian Magpie) or be initiated by a few «urban specialists» that spread with their descendants from one town to the next. In the case of the Eurasian Blackbird, for example, there seems to be a specific type of «urban Blackbird». Such urban colonisation processes are still ongoing today.

In 1993–1996, the Common Woodpigeon only occurred very locally in settlements in Switzerland, with the exception of Geneva and Basel. The further colonisation of urban areas started only at the beginning of the 21st century. To determine the trend in settlements, we compared 85 kilometre squares (1 × 1 km) that lie predominantly in urban areas and were surveyed in both 1993–1996 and 2013–2016. The Woodpigeon population has tripled in these kilometre squares. Thus, the population increase in settlements is much greater than in other habitats (mainly woodland), where numbers «merely» doubled in the same period. So far, there is no indication that the colonisation of cities has reached capacity – the populations in urban areas will presumably continue to grow.

Compared with the rest of Europe, the Woodpigeon was late to colonise settlements in Switzerland. The species began to occupy cities such as Paris and London in the first half of the 19th century. In Germany, colonisation of urban areas was hesitant at first, until the process began to accelerate in the 1960s. Many cities in Sweden and Finland followed up until the 1990s. In many places, the presence of the Woodpigeon extends to the city centres, sometimes reaching remarkable densities of up to 25 pairs/10 ha. The species has lost its fear of humans and behaves much like the feral pigeon. This behavioural adaptation greatly facilitates the colonisation of settlements. A shorter escape distance than in other habitats has been observed in several other species too.

The colonisation of towns by the Woodpigeon is aided by mild winters, the ample food supply, lower predation pressure and the general increase in numbers. In many parts of Germany, the species’ population density is greater in urban areas than in the surrounding woodlands.

Mild winters have resulted in an increase in winter observations in Switzerland ever since the 1990s. Since winter 2003/2004, there has been a sharp increase in records – many of them from settlements. Other species, such as the Blackbird, have probably also wintered in settlements prior to breeding there. Settlements at our latitude offer advantages for wintering birds because they are somewhat warmer than the surroundings and food is provided by humans directly or indirectly (e.g. feeding, rubbish, berries, snow removal).

Several other species have gained a foothold in settlements. The colonisation of towns by the Yellow-legged Gull, for example, is also associated with a marked population increase. In 2016, about ten times as many Yellow-legged Gull pairs bred in Switzerland as in 1993–1996. While roof nesting was first recorded back in 1994 near Versoix GE, the number of breeding records in settlements, mostly on flat roofs, increased mainly between 2013 and 2016, almost tripling in that period. In 2016, 104 broods were counted on buildings. Compared to natural breeding sites, predation pressure is probably lower on flat roofs. On the downside, roof-nesting birds have to cope with higher temperatures. But the benefits clearly outweigh the disadvantages, as roof-nesting birds are prepared to fly large distances to their feeding grounds near water or on farmland.

Some species have inhabited European cities for centuries. In Switzerland, the process has been slower. In Germany, for example, many more species are known to inhabit settlements, such as Dunnock, Song Thrush, Eurasian Jay, Crested Tit, Common Chiffchaff and Northern Wren, and even raptors like Eurasian Sparrowhawk, Northern Goshawk, Eurasian Eagle-owl and Northern Long-eared Owl. So far, these species are absent from gardens and parks in Switzerland, or at most breed occasionally. The reasons are not known, though the larger size of parks and gardens in Germany may be an advantage. In any case, it will be interesting to see which species shows up next in our green spaces. To make sure this happens, we need to preserve large trees and remaining near-natural habitats despite increasing urban density, and manage gardens and parks in a way that encourages biodiversity.

Albrecht, P. (1996): Première nidification en Suisse du Goéland leucophée (Larus cachinnans) sur un bâtiment. Nos Oiseaux 43: 302.

del Hoyo, J., A. Elliott, J. Sargatal, D. A. Christie & E. de Juana (2017): Handbook of the birds of the world Alive. Lynx Edicions, Barcelona. https://www.hbw.com (22.11.2017).

Evans, K. L. (2010): Individual species and urbanisation. S. 53–87 in: K. J. Gaston (Hrsg.): Urban ecology. Cambridge University Press, Cambridge.

Evans, K. L., K. J. Gaston, S. P. Sharp, A. McGowan, M. Simeoni & B. J. Hatchwell (2009): Effects of urbanisation on disease prevalence and age structure in blackbird Turdus merula populations. Oikos 118: 774–782.

Evans, K. L., B. J. Hatchwell, M. Parnell & K. J. Gaston (2010): A conceptual framework for the colonisation of urban areas: the blackbird Turdus merula as a case study. Biol. Rev. 85: 643–667.

Fey, K., T. Vuorisalo, A. Lehikoinen & V. Selonen (2015): Urbanisation of the wood pigeon (Columba palumbus) in Finland. Landsc. Urban Plan. 134: 188–194.

Flade, M. (1994): Die Brutvogelgemeinschaften Mittel- und Norddeutschlands. Grundlagen für den Gebrauch vogelkundlicher Daten in der Landschaftsplanung. IHW-Verlag, Eching.

Fredriksson, R. & M. Tjernberg (1996): Upplands fåglar – fåglar, människor och landskap genom 300 år. Upplands Ornitologiska Förening, Uppsala.

Gedeon, K., C. Grüneberg, A. Mitschke, C. Sudfeldt, W. Eikhorst, S. Fischer, M. Flade, S. Frick, I. Geiersberger, B. Koop, K. Bernd, M. Kramer, T. Krüger, N. Roth, T. Ryslavy, S. Stübing, S. R. Sudmann, R. Steffens, F. Vökler & K. Witt (2014): Atlas Deutscher Brutvogelarten. Stiftung Vogelmonitoring Deutschland und Dachverband Deutscher Avifaunisten, Münster.

Glutz von Blotzheim, U. N. & K. M. Bauer (1966–1997): Handbuch der Vögel Mitteleuropas. Bd. 1–3 von K. M. Bauer & U. N. Glutz von Blotzheim bearbeitet, Bd. 4–7 von U. N. Glutz von Blotzheim, K. M. Bauer & E. Bezzel sowie Bd. 8–14 von U. N. Glutz von Blotzheim & K. M. Bauer. Mehrere Bände seither in der 2., durchges. Aufl. Akademische Verlagsgesellschaft, Wiesbaden (bis 1982) bzw. Aula, Wiesbaden.

Isaksson, C. (2015): Urbanization, oxidative stress and inflammation: a question of evolving, acclimatizing or coping with urban environmental stress. Funct. Ecol. 29: 913–923.

Møller, A. P. (2008): Flight distance of urban birds, predation, and selection for urban life. Behav. Ecol. Sociobiol. 63: 63–75.

Müller, C. (2017): Seltene und bemerkenswerte Brutvögel 2016 in der Schweiz. Ornithol. Beob. 114: 147–160.

Partecke, J., I. Schwabl & E. Gwinner (2006): Stress and the city: urbanization and its effects on the stress physiology in European blackbirds. Ecology 87: 1945–1952.

Rabosée, D., H. de Wavrin, J. Tricot & D. van der Elst (1995): Atlas des oiseaux nicheurs de Bruxelles. Aves, Liège.

Rutz, C. (2008): The establishment of an urban bird population. J. Anim. Ecol. 77: 1008–1019.

Schmid, H., R. Luder, B. Naef-Daenzer, R. Graf & N. Zbinden (1998): Schweizer Brutvogelatlas. Verbreitung der Brutvögel in der Schweiz und im Fürstentum Liechtenstein 1993–1996/Atlas des oiseaux nicheurs de Suisse. Distribution des oiseaux nicheurs en Suisse et au Liechtenstein en 1993–1996. Schweizerische Vogelwarte/Station ornithologique suisse, Sempach.