Ornithologists visiting an island find two species of birds that appear nearly identical except for bill size. Which of the following is the most likely explanation for their discovery?

A) Mutations have resulted in an inferior species with defective bills.
B) Coevolution of the two species has resulted in resource partitioning between the species.
C) They are not separate species.
D) There is natural random variability.
E) The birds need camouflage for protection from predators.