Question

what was the main reason for the severe decline in the bald eagle population in the mid - 1900s?
chemicals such as ddt caused thinning of egg shells which caused the population to decline.
hunters found that eagles were good to eat and began harvesting them to sell to restaurants.
bald eagles were unable to compete with other birds so they moved to other continents.

Explanation:

DDT, a pesticide, biomagnified in the food - chain. In bald eagles, it led to egg - shell thinning, reducing hatching success and causing population decline.

Answer:

Chemicals such as DDT caused thinning of egg shells which caused the population to decline.