A population of birds lives on a small island. Another population of the same species lives on the mainland. The distance between the island and the mainland is too great for birds to fly back and forth. Recently, a series of
sandbars and tiny islands have formed between the island and the mainland.

The birds can now reach the Island.

Explanation:

The birds can now reach the Island because there is a sandbars and tiny Islands where they can rest for sometime as well as feed on the insects present at that sandbars and tiny Islands. Before these sandbars and tiny islands, the birds can't reach to the mainland due to large distance between Island and mainland so they have no capability to fly such large distance until the tiny Island and sandbars are appeared in the ocean.

an adaptation is a change or process by which an organism takes to be better suited for its environment. for example; migration is a behavioral adaptation, this is needed because birds are not built to last extremely cold climates. there are different adaptations because there are different species needing to adjust to different things, bears don't migrate; they hibernate.