Question

How has DDT caused a decline in bird population?

Answer 1

DDT

Dichloro diphenyl trichloroethane (DDT) is an insecticide which was used indiscriminately in the past.

DDT and biomagnification

DDT accumulates in the adipocytes of the organisms and increases in concentration at successive trophic levels. This is because it cannot be metabolised or excreted, hence, passed on to the next higher trophic level. This is called biomagnification.

Effect of DDT on birds

DDT was used as insecticide in agriculture and released in water bodies, so it accumulated in fishes as well as the birds feeding on these fishes.
This accumulation of DDT caused infertility and thinning of eggshells that resulted in decline in bird population.