Early one spring, a group of bird-watchers counted 30 different species of birds in a tract of forest. In the early spring two years later, the bird-watchers counted 15 species in the same area. Which statement best summarizes this situation?
Birds follow different migratory paths each year.

The forest shows a decrease in biodiversity.

Human beings disrupt the presence of animals in ecosystems.

It is important to study living things to better understand the earth