Answer:
Migration of squirrels.
Explanation:
Migration of squirrels can cause decrease in population in an area.
Squirrels migrate or move for one place to another which can be as a result of drought, food shortage or overpopulation.
Squirrels tend to migrate from an area to another in search of food for living. They also move when there is drought to get water and when their population in an area much, the migrate to get another space.
