The drastic decline in the number of Kirkland's warblers, prompting the U. S. Forest Service to include the Kirtland’s warbler on the list of endangered species in 1967 under the Endangered Species Preservation Act of 1966 was A) eggshell thinning due to DDT use.
B) habitat loss as young Jack pine forests matured.
C) competition for food among the other northern bird species.
D) the increase in wildfires that destroyed the developing Jack pine forests.