Indirect selection is when one partner chooses a mate based on just one thing that is related to how fit and healthy the mate is all together. "H. arborea" is a frog that is awake at night, and the females listen to the males sing and then choose one, so the frogs must be able to hear well. These frogs can also see well in low light. This ability to see may be related to how females choose males. Scientists say female "H. arborea" choose males with more brightly colored vocal sacs. They think colorful vocal sacs may show that the frog has enough carotenoids in the food it eats. This may mean the male frog is better at finding food than other frogs, and he might pass on some of this skill to his offspring.