Urban Adapters and Avoiders Model
The terms “urban adapters” and “urban avoiders” serve to categorize bird and animal species according to their ability to survive and even thrive in urban environments.
McKinney acknowledges that there can be many ways to group species along a gradient, but that many bird and mammal studies agree upon three main classifications (887): urban avoiders, urban adapters, and urban exploiters.
Urban adapters, as a category, is fairly self-explanatory. Adapters are birds or animals that are able to adapt their lives to the city environment. They are able to find and use sources of food and shelter found in urban environments. They thrive especially in suburban conditions, where back yards and empty lots provide a venue as well as resources for adapter species to exploit.
Plant species such as dandelions and other weeds, or early successional species that either establish themselves quickly or are planted by people are adapters. Suburban developments tend to be managed to closely resemble savanna or grassland, so those species do well here. bird species in this category are often “edge” species, able to comfortably move between forested and open spaces. They also tend to be omnivorous, and thus able to take advantage of the many sources of food available to them in the typical suburban yard. They thrive also in part because their natural predators fall into the “avoiders” category, and are not welcome in human-controlled environments.
Mammals can exist in urban areas in several ways: some burrow underground, protecting themselves from people while taking advantage of human-provided resources; others, such as raccoons, need fragments of forest area, but on the whole take advantage of human proximity to exploit resources such as garbage and vegetable gardens. These species also benefit from a lack of natural predators, as those predators are often not welcome where people make their homes.
Avoiders, on the other hand, do not do well in urban environments. This can be for several reasons. On one hand, they may not be able to find the food and shelter resources they need outside of large tracts of their natural habitat; they tend to be sensitive to disturbances to their habitat (887). Another reason is that they may be considered hostile or dangerous to people, and thus are actively discouraged from moving into cities. Large mammals tend to fall into this category; deer and moose, for example, do not tend to do well in cities, while wolves or bears are relocated when they wander in. Old-growth forests and wetlands – often drained to make way for farmland – are vegetative species that fall into this category.
Another category exists: urban exploiters or invaders. These creatures, of which rats are a good example, find urban environments so hospitable that they exist in much larger numbers inside of cities than anywhere else. They are in fact often very, if not totally, dependent on human resources and intervention. Urban environments not only provide all the food resources they need, but also often serve to eliminate predators that would normally keep the populations of these exploiter species in check. Exploiter species tend
to do well in whatever urban environment they happen to be in, and so are in many cases a global presence, transcending native regions. Plants species in this category are resistant to pollution and trampling, can survive and grow even in paved areas, and tend to have wind-dispersed seeds.
McKinney, Michael. L. “Urbanization, Biodiversity, and Conservation.” BioScience
45:10 (October 2002): 883-890.