What Makes Some Birds Urban Exploiters?

By Fizala Tayebulla

Keywords: Urban Exploiter, Urbanized Area, Behavior, Trait

The growth of urban topography encompasses corresponding shifts of all its associated elements and features – even biodiversity. A question to be asked is, how species characterize themselves within landscapes marked by varying degrees of urbanization? In the subject of Urban Ecology, there are two broad categories of fauna, the ‘generalists’ which have less sensitivity to human disturbances (e.g. Cockroach, Rat) as opposed to ‘specialists’ which have a narrower range of tolerance (e.g. Frog, Sword-billed Hummingbird). Generalists can then further be studied in relation to urban spaces, forming particular groups that are clubbed as urban exploiters, suburban adapters and urban avoiders. Communities of species that dominate urban areas with almost exclusively native vegetation are termed as ‘urban avoiders’. In areas with transitional vegetation (both native and non-native), the group of species that dominate here are termed as ‘suburban adapters’. While the community of a smaller number of species which dominate the most urbanized areas (built-up area coverage) are termed as ‘urban exploiters’ (Kark, Iwaniuk, Schalimtzek, & Banker, 2007).

 ‘Species thriving as urban commensals to the point that they become dependent on urban resources.

-Schochat et al.

Picture1

Figure 1 Illustration of lines of abstract birds in the backdrop of built-up area (Credit: Fizala Tayebulla/CUES)

As cities develop, more natural habitats are fragmented (and lost), which has expected impacts on the richness of species along a slope of urbanization. While several pieces of research show that richness peaks at intermediate levels of urbanization. Given that not all species are pre-adapted to urbanized environments, one may wonder what sets apart some bird species to inhabit intensely ‘developed’ spaces.

Studies show that these species are highly social for observed features like foraging in groups for an enhanced search to locate food, to guard against predatory species and to overcome competition, thus improving the chances of survival. Migratory habits are found to be on a steady decline with increasing urban adaption, rendering urban exploiters as sedentary. Their dietary habits change from being primarily seed and fruit-based to becoming granivorous, omnivorous or insectivorous. A sustainable food source for birds which are urban exploiters is garbage dumps in cities. Another significant behavioural change can be seen in nesting behaviour where urban exploiters are found to be more likely to nest on rocks/concrete than on trees/vegetation.

The answer to what makes some species exploiter appears to be based on a combination of traits and complex interactions between these traits and humans. Identifying such traits may help us map biotic homogenization in terms of attaining a scope for prediction, mitigation and maybe even the inclusion of urban areas in future conservation and biogeographical studies (Bonier, Martin, & Wingfield, 2007).

References:

  • Bonier, F., Martin, P. R., & Wingfield, J. C. (2007). Urban birds have broader environmental tolerance. Biology Letters, 3(6), 670–3. http://doi.org/10.1098/rsbl.2007.0349
  • Kark, S., Iwaniuk, A., Schalimtzek, A., & Banker, E. (2007). Living in the City: Can Anyone Become an “Urban Exploiter”? Source Journal of Biogeography, 34(4), 638–651. Retrieved from http://www.jstor.org/stable/pdf/4640539.pdf

Leave a Reply