How Ddt Harmed Hawks and Eagles

Pesticide DDT is a chemical compound that was a major factor in reducing the eagle and hawk populations around the world. Raptors were also hurt by other problems such as hunting and deforestation. The 1972 ban of DDT certainly contributed to the bird of prey’s revival in the United States. It is important to understand how people have tracked and identified their progress. The modern day explosion of nesting pairs makes us realize the disastrous effects of synthetic pesticides.

The United States used DDT during the mid-1900s. During and after World War II (1939–45), DDT was widely used as a synthetic pesticide to prevent insects from killing agricultural crops. It was popular with farmers, foresters and domestic gardeners. The compound reached a global peak of 386 million pounds (175 million kilograms) in 1970. In 1959, the United States sprayed 79 million pounds (36 million kilograms) of DDT chemical compound.

The dangerous consequences of spraying synthetic pesticides were not realized until 1962. An American biologist, Rachel Carson published Silent Spring. The public learned DDT caused cancer in people. The synthetic pesticide harmed eagles and other birds of prey populations. Bald eagles were threatened with extinction in the lower 48 states. Finally, in June, 1972, the US Environmental Protection Agency (EPA) banned DDT use in the United States. Recently as May 23, 2001, DDT pesticide use was limited worldwide at the Stockholm Convention.

Birds of prey species badly affected by synthetic pesticide use included: Peregrine Falcons, Sharp-shinned Hawks, Cooper’s Hawks, Eurasian Sparrow hawks, Osprey, Bald Eagles, White-tailed Eagles, Brown Pelicans and herons.

The eagle needs rich soil and its fertility. Grass cannot grow on deteriorated soil. A diminishing rabbit population hurts eagle populations. DDT contaminated many soils and plants. Mice stored the poisonous particles in their fatty tissues. Hawks consumed numerous mice, and their numbers declined because of DDT poisoning.

Bald eagle populations decreased as low as 500 nesting pairs in the lower 48 states. Some bald eagles were poisoned because their fish ingested synthetic pesticides. The 1972 DDT ban and the 1973 Endangered Species Act, helped reverse a dismal trend. The lower 48 states noticed an increase of over 5,000 nesting pairs. 70,000 bald eagles inhabit North America.

In 2007, the American bald eagle was taken off the endangered species list in Wisconsin. In 1973, the bald eagle inhabited 108 territories in the state. Those territories rose to 1,150 breeding pairs in 2010. Half of the eagle population nest on privately owned land. It makes it important for Wisconsin citizens to understand the importance of protecting eagles.

In 1950, Florida reported alarming bald eagle declines. The following fifteen years, eagle populations continued to decline throughout the United States. In 1963, it was reported their were only 417 bald eagle breeding pairs. In 1967 the bald eagle was listed as an endangered species under another law; the Bald Eagle was protected throughout the United States south of the 40th parallel. The law preceded the Endangered Species Act of 1973.

Synthetic pesticides prevented birds of prey from incubating eggs. The DDT ingested into the eagles and hawks reproductive system thinned the egg shells of their offspring; the eggs cracked under the weight of an adult eagle who failed to warm and incubate them. 

The DDE compound, Dichlorodiphenyldichloroethylene, causes eggshells to thin or sterile eggs. The stable chemical endures in the environment. It is formed because DDT loses hydrogen chloride (dehydrohalogenation). It is lipid-soluble, and concentrates in animal body fat. Birds use the fat stored in their fatty tissue when it is difficult to find food. It releases all the DDT accumulation which make the bird vulnerable to the lethal synthetic pesticides. Together DDT and DDE are considered toxic for birds of prey reproduction.

DDT changes into many different forms called metabolites. DDE is categorized as a metabolite that inhibits reproductive enzymes in birds. Enzymes aid chemical reactions. They increase or decrease the speed of biological processes. In eagles and hawks, reproductive enzymes affect the quantity of calcium deposited in eggshells. DDE inhibits calcium ATPase in the shell gland membrane, and it restricts the blood flow of calcium carbonate. Eggshells lacking calcium are vulnerable. Female reproductive tract development is endangered by o,p’-DDT; eggshell quality is weakened.

The Cooper’s Hawk population decreased in the eastern United States during the middle of the twentieth century because of constant synthetic pesticide use. They declined because passerine birds consumed DDT. The Cooper’s Hawk consumed too much of the synthetic pesticide. DDT was ingested by many other animals the hawk relied on for food. The Cooper’s Hawk couldn’t absorb enough calcium. Agricultural management was a major problem for all hawk populations in the United States.

Hawk populations are strengthened by captive breeding programs, and protective raptor populations. The bald eagle was placed on the threatened species act of 1994. July 2, 1999, President Clinton announced to the world that bald eagle populations had completely recovered. Bald eagles currently have 5,800 breeding pairs in the United States.

Wisconsin Department of Natural Resources, U.S. Fish and Wildlife Service, and The National Park Service, provide valuable services for raptor recovery.

*Collect data about eagles and birds of prey

*Conduct breeding surveys

*Collected data is mapped in a computer program called “GIS” Geographical Information System

*Volunteers climb nesting trees and put metal leg bands on eaglets, disease and contamination is checked out by taking blood samples of the birds, they check up on dead or injured eagles

*The Department of Natural Resources (DNR) publish educational materials to encourage people to help increase and protect eagle nesting protections

Hawk Watch Sites help stabilize raptor populations

*They monitor population trends nationwide

*The Hawk Migration Association of North America (HMANA) compiles data that monitor bird of prey progress in their region

Vermont set up Hawk Watch Sights on mountains

*Snake Mountain

*Mount Philo

The past 25 years volunteers from Vermont play a major role in data collection. Spring and Fall, volunteers scout broad-winged hawks, red-tailed hawks and sharp-shinned hawks. American kestrels are attracted to the open fields of Vermont. The peregrine falcon, osprey, and bald eagle have reappeared in the region.

Swainson’s hawks are midsized raptors. They migrate yearly between their native North America to certain deserts and South American grasslands. Western populations of Swainson’s hawks declined in the 1970 synthetic pesticide era. It was listed as a threatened specie in California. The Montana Raptor Survey Route has reported hawks thrive in the past three decades.

Red-tail hawks have increased in Essex County, a place their numbers were considered rare fifty years ago.

It is legal to use DDT in other developing countries. Chemical companies continue production marketing of synthetic pesticides. Migratory birds pick up DDT in the south and transfer it back to northern regions. Our eagles and hawks are still threatened by synthetic pesticides.

Bird of prey recovery is strengthened by governmental organizations and strong volunteer groups dedicated to their survival. Banning DDT was a huge step fore ward for the bird species. Bird lovers must continue to avoid over exploiting DDT and similar synthetic pesticides.

References…Vol. 59, No. 2 – 84 pages – Magazine…/Red%20Tailed%20Hawk%20Food%20Chain%20Tag.pdf…/Red-tails-on-the-rise-Hawk-populations-in-Essex-County-