In an area where DDT had been used extensively, the population of birds declined significantly because:

Options

A. birds stopped laying eggs
B. earthworms in the area got eradicated
C. cobras were feeding exclusively on birds
D. many of the birds laid eggs, that did no hatch

Answer

D

Explanation

DDT, its breakdown products and other chlorinated hydrocarbon pesticides pose serious threat to birds. These persistent poisons enter the food chain and they accumulate in the fatty tissues of organisms at lower trophic level and then tend to concentrate in considerably toxic amount as they move up through the food chain. This is called bio-magnification or bio-concentration. It weakens the calcareous egg shell of birds as it becomes very thin.