The Wood Thrush Is a Forest Interior Species, Which Reproduces

The wood thrush is a forest interior species, which reproduces most successfully in areas deep inside the forest.The cowbird is a grassland and forest edge species that has flourished as humans have cut forests and built towns.Cowbirds lay eggs in other birds' nests, and the host birds often raise the larger cowbird nestlings.As cowbird population size and geographic range have expanded, wood thrush populations have declined.Which factor is likely most responsible for the declining wood thrush population?

A) Cowbirds are showing greater aggression.
B) Edge effects are negatively affecting cowbirds.
C) Edge effects are negatively affecting wood thrushes.
D) Wood thrushes are showing less aggression.
E) Habitat loss is forcing wood thrushes to lay eggs in cowbird nests.