Adult Bufflehead ducks in marine environments prefer shrimp. If a Bufflehead duck is foraging in a patch of shrimp, when should they move on to start looking for another patch and why? a. The duck should move on when they are threatened by another duck for their feeding territory, because otherwise they will experience a costly loss. b. The duck should move on when they have the highest relative fitness, because their traits will evolve by natural selection. c. The duck should move on when their cumulative gain is equal to their energy invested in traveling and foraging, because they will have harvested the optimal load. d. The duck should move on when the benefit curve is highest relative to the cost curve, because they have traveled the optimal distance..