In the famous argument between Thomas Jefferson and Benjamin Franklin over the national symbol, they pitted the bald eagle against the turkey. In the end, of course, they chose the great, majestic American bald eagle over that which Franklin praised as “a little vain and silly” bird that nevertheless “would not hesitate to attack a grenadier of the British guards who should presume to invade his farm yard with a red coat on.” For perhaps obvious reasons, Congress decided in favor of the eagle. Around the 1960s, however, the argument in favor of the turkey gained some traction: its continued, flourishing existence set it apart from its former competitor. The bald eagle population had dipped to only 487 nesting pairs in the contiguous United States by 1963. Threats to the eagles’ survival came from a range of sources: illegal hunting, habitat destruction, and, most pernicious of all, the absorption of the pesticide DDT into its food and water sources. DDT accumulated in eagles’ bodies and hindered their ability to produce strong, hard eggshells, with the result that birds trying to incubate and protect their eggs crushed them instead.

In the years following the recognition of the bald eagle’s approaching extirpation in the lower 48 states, various measures passed to protect the national symbol. The most successful of these provisions were the ban on DDT, the habitat protection measures enacted by a variety of smaller acts, and, finally, in 1973 the passage of the more comprehensive Endangered Species Act (ESA). After their addition to the endangered species list, which is comprised of those species closest to extinction, the eagles gradually recouped their numbers and, in 2007, dropped off the “threatened” list where they had been moved after their population was no longer on the verge of extirpation. Estimates by the U.S. Fish and Wildlife Service at the time found at least 9,789 nesting pairs in the contiguous U.S.

Lauded as an ESA success story, the bald eagle population recovery mirrors the recoveries of several other species as a consequence of successful protection measures. One such species is another bird of prey, the Peregrine falcon. Around the 1960s, with the introduction of modern pesticides, the population of the Peregrine falcon declined as much as 90 percent, with only 324 nesting pairs remaining by 1975. Now, due to the same protection measures that saved the bald eagles, there are 2,000-3,000 nesting pairs of Peregrine falcons in North America.

In the Midwest, various organizations have started to document an odd phenomenon: Peregrine falcons nesting in urban environments. The Midwest Peregrine Society estimates that 48% of Peregrine falcon nesting sites appear on high-rise buildings. In New York City, falcons construct their eyries on church steeples, the tops of bridges, and skyscrapers. Doctor Michael Willig, Director of the Center for Environmental Sciences and Engineering at the University of Connecticut, includes the bird among formerly endangered species that have learned to adapt to urban settings: “There are a number of species that can actually acclimate and perhaps even adapt to human-built structures, that benefit from human activities,” he said in an interview with The Politic.

The success of some species in cities is particularly important for their continued survival, as the conservation efforts that have generally proved most successful are those concerned with habitat protection.

Habitat protection and accompanying measures are often intensive endeavors, leading some to wonder why it is vital to devote such tremendous energy and resources to the protection of endangered species. When people think of endangered species, they tend to think of so-called charismatic species: lovable or striking animals such as polar bears, gorillas, tigers, and bald eagles. Just as important, however, are less appealing or little-known species such as the bluefin tuna or the red-tailed parrot.

The problem becomes more complicated with those organisms whose importance (and very existence) are still being discovered. For example, most soil microbes have not been discovered and named. Daily destruction of their habitat prompts questions about the future ramifications of the loss of organisms whose function in an ecosystem is unknown.

“When we lose a particular species, at some level we’re losing a function that the species performs in the environment,” said Willig. “We don’t know what the functions are for most species.”

This phenomenon can severely affect ecosystem services, which play an important role in human society. The loss of one species may compromise the services an ecosystem provides, services that include food and water production, climate or disease regulation, and such supportive mechanisms as nutrient cycles and crop pollination.

Willig used what he calls the “computer analogy” to explain the potentially devastating impact the extinction of certain organisms can have on an ecosystem. He described the analogy as follows: “You own a computer. There are lots of parts in your computer and, if you’re someone like me, you don’t know what most of them do. If you take the back off of the computer, pick any random piece and take it out, it diminishes the value of your computer. At some level, at some time, it’s going to affect its value.”

In a similar way, if the computer is an ecosystem, and through habitat destruction, or chemical poisoning, or another threat a species goes extinct or its population is severely diminished, its loss may have reverberations in the ecosystem far into the future.

“Each species has a particular function to play, we might not even know what that is, and it might not be obvious to us until a disaster in the ecosystem occurs,” said Willig. “The fear is if you don’t understand the system and you start tinkering with it, you’re likely to make mistakes. You want to protect those species from going extinct because it’s likely, at some time or another, they’ll play a vital role in the community.”

Willig explained that measures like the ESA protect those parts when population trends suggest that, if unassisted, a species will go extinct. While the ESA’s success with species like the bald eagle, the Peregrine falcon, and the gray wolf should be applauded, the success ought to be viewed in context.

“One success does not mean the whole process is successful,” Willig said. “It tells you that human intervention can make a difference. It doesn’t tell that a particular intervention makes a difference for all species.”