These pesticides, which are used to kill insects by affecting their nervous systems, have three characteristics that also make them harmful to birds of prey. Persistent pesticides stay in the environment for long periods of time before disappearing. DDT, for example, has a half-life of fifteen years. This means that after fifteen years, half of the amount of pesticides released still remain in the environment. A broad spectrum compound is designed to kill a variety of pests.
Farmers spray their crops.
An insect pest consumes the pesticide, while eating the crop, and concentrates the fat-soluble pesticide in its fatty tissue. The insect is eaten by another animal, which also concentrates the already once-concentrated pesticide in its fatty tissue. That animal is then eaten by another animal, which concentrates the twice-concentrated pesticide in its fatty tissue. As a result of biomagnification, the animals at the top of the food chain acquire a higher percentage of the compound than does the insect that originally consumed it. This is a problem for birds of prey.