The writer is considering deleting the first part of the preceding sentence, so that the sentence would read:
Early spring is generally the first opportunity to observe the Wood Thrush in the United States.
If the writer were to make this change, the essay would primarily lose:

A. Details that indicate to the reader what will eventually happen.
B. The contrast between the appearance of the Wood Thrush and the appearance of other forest birds.
C. An example of one of the features that makes the Wood Thrush such a special bird.
D. An indication of why bird watchers will usually see the Wood Thrush only during certain times of the year.