What does this sentence mean: Jefferson was so taken with his birds.?

It means Jefferson was charmed by his birds.

Explanation:

Hope this helped! ^   ^

remember, the goal of an adjective clause is to add more information to a noun or a pronoun. as you can see from the examples above, you can add information by including a longer adjective clause or tighten up a sentence by turning the adjective clause into an adjective phrase.