Fixed the OA above.

The OA is B

Premises:

Male bowerbirds construct elaborately decorated bowers.
Different local populations of bowerbirds of the same species build bowers that exhibit different building and decorative styles,

Conclusion: The bowerbirds' building styles are a culturally acquired, rather than a genetically transmitted, trait

We need to strengthen the conclusion.

A. There are more common characteristics than there are differences among the bowerbuilding styles of the local bowerbird population that has been studied most extensively.

This tells us that there are more similarities than differences. This doesn't strengthen our argument at all. If anything, it weakens it by implying that quite a bit could be genetically transmitted since there are more similarities.

B. Young male bowerbirds are inept at bowerbuilding and apparently spend years watching their elders before becoming accomplished in the local bower style.

If bower building were a genetically transmitted trait, young bowers would have known how to build. But they do not and instead they acquire the skill by watching elders. This strengthens our argument that bower building skill is culturally acquired. Correct.

C. The bowers of one species of bowerbird lack the towers and ornamentation characteristic of the bowers of most other species of bowerbird.

We are not comparing bowers of different species. We are talking about different local populations of the same species. Even if bower building were genetically transmitted, the genes of one species would be different from those of another so genetic transmission would be perfectly valid. Hence this option doesn't help us strengthen our argument that bower building is culturally acquired and not genetically transmitted.

D. Bowerbirds are found only in New Guinea and Australia, where local populations of the birds apparently seldom have contact with one another.

Whether they have contact or not doesn't matter. Whether they are in contact or no would have been useful to know if we were to show why there are similarities in bower building styles (Close contact with other populations could have been the reason for similarities) or if we were to prove that it is a genetically transmitted trait (far apart but similarities could have strengthened the case for genetic acquisition). The building styles are different so it doesn't matter how close or far apart the populations are.

E. It is well known that the song dialects of some songbirds are learned rather than transmitted genetically.
Out of scope.

Answer (B)