Question

there is a decline in population of fish eating Birds when the water bodies near and agricultural field is it true why

Answer 1

The reason for decline in fish-eating birds is biomagnification of toxic substances like DDT and other pesticides from the agricultural fields.

The pesticides are applied in the fields for protection of crops. These get washed off to water bodies with irrigation water and rain and are indirectly consumed by the fishes in the water, thereby entering the food chain. These toxic chemicals get accumulated and their concentration increases with each trophic level. Thus, on reaching fish-eating birds, their concentration will be increased many folds.

The high concentration of DDT interferes with calcium metabolism in birds and causes thinning of eggshells and their premature breaking, ultimately causing decline in bird population.

Answer 2

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★ Reason :

Yes, there is a decline in the population of fish-eating birds when the water bodies are close to agricultural fields. This happens due to a process called Biological magnification or Biomagnification. This process refers to the increase in concentration of toxic materials like DDT progressively at each trophic level of a food chain.

● Explanation :

Toxic materials like DDT and several other pesticides are constantly used in agricultural fields. This leads to an increase in the concentration of such toxic materials in the fields.

During the monsoon season, theses materials get washed away from the fields to the water bodies (which are close to the agricultural fields). This results in the increase of concentration of toxic materials in the water bodies.

From the water, these materials are consumed by aquatic plants and further, these plants are consumed by fishes. These fishes are finally eaten up by the fish-eating birds. As these birds occupy the top most position in an aquatic food chain, the concentration of toxic materials will be the largest in them. This disturbs the calcium metabolism in birds, which causes thinning of eggshells and their premature breaking, ultimately causing decline in bird population.