by Whit Gibbons

August 23, 2009

Last week I wrote about the abundance of wild animals that seem to have been showing up in residential neighborhoods in many parts of the Southeast. Some are perceived as nuisances, including armadillos that burrow, coyotes that might have an interest in a pet cat as a meal, and deer that eat shrubbery and the vegetables in your garden. All of them are more common and, some folks think, more brazen than in the past. What are the reasons for wildlife's newfound interest in moving into suburban neighborhoods?

I noted two reasons that I think help explain the phenomenon: leash laws, which eliminate dogs as control agents, and the reduction in widespread use of certain pesticides and herbicides that kill a wide variety of harmless insects and other invertebrates. The return of peregrine falcons to many parts of the country, and their presence in some urban areas, can be attributed to DDT restrictions in the United States. DDT was implicated in the near extinction of these birds of prey by damaging their eggs shells.

But other factors may also be instrumental in the perceived upsurge in residential wildlife. One of these is the vegetational maturity of many neighborhoods. Older, more established residential areas in a community typically have larger shrubs and trees than when they were first developed, leading to more wildlife habitat. The practice of removing all trees from a woodland habitat before building houses may decrease construction costs; it certainly guarantees that no wildlife will remain. But in many instances, over the decades, vegetation returns to these denuded areas and green habitat flourishes once again, attracting wildlife. An interesting comparison these days would be the number of wildlife sightings in housing areas established during the last decade with older neighborhoods that have had time to become revegetated.

Another reason for more wildlife being observed these days is that our overall environmental outlook has changed: more people have a positive attitude toward protecting wildlife. As a result, people in a community are more likely to support efforts to retain undeveloped habitats, especially wetlands and natural woods, where native species can flourish. Concomitant with that is a greater familiarity with and interest in learning about wildlife, so that wild animals are more likely to be noticed.

Yet another possible cause for some wildlife in residential areas is that certain species may have actually "learned" how to coexist with humans and have adapted to new opportunities for feeding (garbage cans), hiding (beneath porches and houses), and nesting (eaves, chimneys) that are absent in wild habitats. Also, the question is being asked among wildlife researchers whether some animals (namely snakes, turtles, and mammals) might actually learn to avoid crossing highways, which is often a costly behavior. Or, if road-crossing tendencies have a genetic component, maybe those that avoid roads are more likely to survive and produce offspring that inherit road-avoidance behavior.

A final reason for why certain larger animals seem more abundant than they once were is they have been able to expand their original geographic ranges or to reinhabit areas where they had been exterminated earlier. Range expansion might occur because former predators have been eliminated (such as mountain lions) or new food sources have become available (such as agricultural crops).

Whatever the reasons may be, it is clear that natural adaptations by certain species have permitted them to successfully adjust to human inhabitation of a large portion of the country. The other side of that coin is that many species are not effective at adapting to the presence of human habitation. For example, rainbow snakes, spotted turtles, and bobcats are much less likely to have populations that thrive in suburban areas because some of their essential resources are typically eliminated. Rainbow snakes and spotted turtles are beautiful creatures, but the former depend on a constant supply of America eels for food and the latter require protected wetland habitats. Bobcats meanwhile require extensive woodlands or swamp forests. We need to maintain as many wild areas as we can so that more sensitive species can persist along with the ones we already see in the neighborhood.

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