How DDT pushed bald eagles to the brink of extinction
Bald eagles may seem like a stretch for a gardening column, but, read on.
In 1939, the chemist, Paul Müller, synthesized the chemical insecticide DDT (dichlorodiphenyltrichloroethane). He worked as an independent scientist for the Geigy Corporation on ways to protect clothing from insect damage, as well as a safer seed disinfectant. In those days, highly toxic compounds made from mercury, arsenic and cyanide were the most common types of insecticides.
Müller was motivated by a severe food shortage in Switzerland, as well as malaria epidemics in Russia and elsewhere, made worse by the beginning of World War II. Müller’s work to combat insect-borne diseases won the Nobel Prize in medicine. In the winter of 1943-44, 1.3 million people were treated with DDT to defeat a typhus epidemic in Naples.
DDT was regarded as a “miracle” compound that would save the world’s food supply from insect pests and eliminate insect-vectored diseases, while posing no harm to humans. As the National Academy of Sciences said in the 1970s, “to only a few chemicals does man owe as great a debt as to DDT … in little more than two decades, DDT has prevented 500 million human deaths, due to malaria, that otherwise would have been inevitable.”
Unfortunately, the widespread use of DDT did have some negative side effects, or more accurately, one of the compounds it breaks down into, DDE (dichlorodiphenyldichloroethylene). DDE affects the reproductive process of predator birds as it becomes concentrated up the food chain, causing the eggs shells to break before the eaglets hatched. DDE in water was absorbed by algae, passed on to algaeeating fish and then bigger fish, and finally, top-of-thefood-chain raptors. The number of eagles, hawks, and other birds high on the food chain declined precipitously after its introduction. DDT is also remarkably persistent in the environment, with a halflife of 150 years in aquatic environments.
Bald eagles, our national symbol, were already at risk as long ago as the 1920s, but DDT seemed to be accelerating their decline. In 1972, the newly formed Environmental Protection Agency banned its use in the US.
Now it is time for a flashback from this old man columnist. As a child growing up in the 1950s and ‘60s, I recall that it was not only acceptable but absolutely necessary for farmers to shoot and kill all birds of prey, whenever sighted. Eagles, hawks and owls were all considered “chicken killers” and therefore they needed to be killed and nobody questioned the practice. It is debatable whether banning
DDT alone saved these birds from extinction, or whether societal attitudes, in general, have helped to bring them back.
In any case, it is true that bald eagles have returned from the brink of extinction and we all now have the opportunity to view these magnificent birds. I recall in the early 1970s waiting in a line in Everglades National Park for hours, just to get a glimpse of a bald eagle nest. This past summer I saw bald eagles almost weekly near my home by the Catskill creek in Preston Hollow, as well as near the Hudson River, the Schoharie reservoir and the Ashokan reservoir. Their success is a result of deliberate restoration attempts by conservation departments nationally as well as federal protection.
Bald eagles are among the largest species of raptors that exist in North America. They are easily identified by their white-feathered heads (not bald, as vulture heads are) and tails with a uniformly black body. Their wingspan is often as wide as 7 feet and their hooked yellow beaks and huge talons make them appear even more formidable. They are almost always found near waterways, where they feed on fish, both dead and alive, snakes, turtles, ducks, rabbits, muskrats and other carrion (dead animals). They swoop down on prey and can carry away even large animals in their long talons. The hooked beaks allow them to easily tear their food apart. Flying at speeds of 40 mph, they can reach 100 mph when attacking and can soar to 10,000 feet in elevation. They have incredible eyesight. “Eagle eye” is a legitimate compliment!
Immature bald eagles do not have the characteristic white head and tail feathers that the adults do. It requires four to five years before they are able to mate, after an elaborate courtship behavior, and once paired, they remain that way until one partner either dies or disappears. Their nests, called eyries, are made of sticks and are constantly enlarged, sometimes exceeding 7 feet in diameter and more than 2 feet deep. An eagle nest can weigh as much as a ton!
Anyone reading this column is within easy viewing range of a bald eagle and I would encourage you to look for one. It is a thrill to see them!