Birds and Urbanization

It’s no surprise that the global human population is growing rapidly. Currently there are about 7.5 billion of us, up from 5 billion just 30 years ago, and one billion only about two centuries ago (1). This drastic demographic transition has been accompanied by an equally striking migration of humans from rural areas to large urban settlements. In 2014, 54% of us lived in urban areas, compared to 34% in 1960 (2). Such a massive shift has literally changed the face of the Earth, transforming forests, swamps, and deserts into the sprawling concrete and steel of urban infrastructure. The changes of these landscapes have had a profound effect on the wildlife whose natural habitat has been converted into an urban space, their behavior, their success, and their survival.

Percentage of Total Population Living in Urban Areas, 2005 (3)

Avian habitats have been reduced, broken up, and degraded as a result of land cover changes in urban areas, but urbanization leads to a variety of outcomes among different species of birds (4). Generally speaking, urbanization seems to favor diversity of non-native over native avian species. Through urbanization, favorable habitats for non-native species are often created, and such species are more likely to be imported into native ecosystems (5). Furthermore, urbanization often results in the homogenization of bird species, as conditions in the physical environment of cities tend to favor certain traits, and thus the same bird species can appear in many different cities (5).

The common pigeon (Columba livia), native to Europe and west Asia, is abundant in urban areas worldwide (6).

Birds adapted to urban environments tend to have an omnivorous diet, display sedentary behavior, are non-territorial, and live in large groups (7). These common characteristics favor the high densities of birds seen in urban areas (8). Bird density is also closely linked to vegetation. While the density of native birds shows a strong correlation with the volume native vegetation in an area, non-native bird density may be related with urban residential lawns, whose adjacent developments provide these city dwellers with roosting sites (9).

In order for native birds to remain successful in urban areas, both their diversity and abundance must be preserved (10). Native species should be protected first and foremost, while some non-native species should be deterred. I think urban design should focus on incorporating native vegetation so that the presence and needs of native bird species are favored over those of non-native species. This could potentially include creating vegetated buffer zones along waterways or establishing dense native forests in or near urban centers, among other possibilities.

References:

  1. Population, total. http://data.worldbank.org/indicator/SP.POP.TOTL (accessed March 26, 2017).
  2. Urban population growth. http://www.who.int/gho/urban_health/situation_trends/urban_population_growth_text/en/ (accessed March 26, 2017).
  3. Watkins, K. Human Development Report 2007/2008; Human Development Report; Palgrave Macmillan: New York, NY, 2007.
  4. Marzluff, J. Worldwide urbanization and its effects on birds; 1st ed.; Springer US: Boston, MA, 2001; pp. 19–47.
  5. McKinney, M. Biological Conservation 2006, 127, 247–260.
  6. IUCN Red List of Threatened Species.
  7. Croci, S.; Butet, A.; Clergeau, P. The Condor 2008, 110, 223–240.
  8. Clergeau, P.; Savard, J.; Mennechez, G.; Falardeau, G. The Condor 1998, 100, 413–425.
  9. Mills, G.; Dunning, J.; Bates, J. The Condor 1989, 91, 416.
  10. Aronson, M.; La Sorte, F.; Nilon, C.; Katti, M.; Goddard, M.; Lepczyk, C.; Warren, P.; Williams, N.; Cilliers, S.; Clarkson, B.; Dobbs, C.; Dolan, R.; Hedblom, M.; Klotz, S.; Kooijmans, J.; Kuhn, I.; MacGregor-Fors, I.; McDonnell, M.; Mortberg, U.; Pysek, P.; Siebert, S.; Sushinsky, J.; Werner, P.; Winter, M. Proceedings of the Royal Society B: Biological Sciences 2014, 281, 20133330–20133330.

Image Citations:

— Unknown. World map showing the percentage of citizens living in an urban environment in 2005. https://commons.wikimedia.org/wiki/File:Urban_population_in_2005_world_map.PNG (accessed March 26, 2017).

— Unknown. LabRoots. https://www.labroots.com/trending/plants-and-animals/4210/study-pigeons-learn-recognize-real-words (accessed March 26, 2017).

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