In Optimizing Foraging,birds Often Stop Feeding in an Area and Move

In optimizing foraging,birds often stop feeding in an area and move on even though there are still some seeds left.What is the best explanation for this observation?

A) They are safer from predators when moving
B) They are more likely to find a mate if they move around
C) Other areas may have food at a lower density
D) The density of the food becomes low, so it will take too much energy to find
E) They will leave some seeds to create the next generation of plants