Before DDT, Peregrine Falcons nesting on the east coast of North America could expect to raise an average of three chicks per nesting attempt each year. After DDT use became widespread in the 1940s and 1950s, reproductive success plummeted. By the late 1960s, many pairs of falcons weren’t raising chicks at all. Most were laying thin-shelled eggs that broke during incubation or that produced chicks too weak to survive. Eggshell thinning was also affecting other birds of prey, including Bald Eagles, Ospreys, Brown Pelicans, and Great Egrets.
DDT’s Toxic Cascade
As top predators, Peregrine Falcons sat at the top of a food chain that magnified DDT’s harmful effects in the environment. DDT accumulates in fatty tissues; the higher it moves up the food chain, the more concentrated it becomes. When prey that had been exposed to DDT or its breakdown products were consumed by predators such as falcons, the concentrations in the predators increased. Peregrines exposed to high enough levels of DDT experienced toxic effects that interfered with their ability to carry out basic life processes such as reproduction.