Survival of a species

This peregrine falcon is identified by the bands on his leg (see inset) as an adult male named Joe, hatched May 13, 2005, in Chicago. Photo: Marek Proga

Last week, the Illinois Department of Natural Resources announced that the peregrine falcon was no longer in need of listing as a threatened species in Illinois. Although it is still protected by the federal Endangered Species Act and the Migratory Bird Treaty, these birds are now present in sufficient numbers to “go it alone” in Illinois without formal state protection. This has to be regarded as a success story, because 30 years ago the prospects for the species were dim indeed. Peregrine falcons are demanding in their habitat needs — they prey almost exclusively on other birds (they were known at one time as “duck hawks”), and they naturally inhabit cliff sides. As humans moved in, the habitat shrank.

Before the use of the pesticide DDT was banned in the early 1970s, bioaccumulation of the chemical led to weak eggshells and high levels of nest mortality among raptors such as the peregrines. The parents literally squashed the weak-shelled eggs before they could hatch. The peregrine population, especially in the Midwest United States, has rebounded spectacularly since then. This is also part of a larger story about successful protective laws and programs. There are still many, many species on various state and federal threatened and endangered lists, but there have been successes as well. It is worthwhile to step back and examine how and why success occurs.

The reason there are so many species in the world is the fundamental ability of plants and animals to adapt to their ecological conditions and pass on successful adaptations to their offspring. This basic tenet of natural selection results in the proliferation of thousands of species as generation after generation is exposed to slightly different conditions. Even when those conditions are the result of human interference, individuals can sometimes succeed by exploiting an “unnatural” habitat. In the case of the peregrine falcon, high-rise buildings and a plentiful supply of pigeons in the city were an adequate substitute for cliffs and ducks. Falcons further exploited their urban environment by constructing their nests on building ledges high above the city streets.

A second source of success is a variety of programs enabled by protective legislation and implemented by various government agencies and volunteer organizations. For the peregrine falcon in Illinois, the Chicago Peregrine Program, operated from the Field Museum in Chicago, became the epicenter of falcon recovery. There is a certain poetic justice when humans get together and work to protect an endangered population and bring it back to healthy levels after historically creating the conditions that put it in jeopardy in the first place.

Rod Walton