Critical Reasoning

Kate: The recent decline in numbers of the Tennessee warbler, a North American songbird
that migrates each fall to coffee plantations in South America, is due to the elimination of
the dense tree cover that formerly was a feature of most South American coffee
plantations.
Scott: The population of the spruce budworm, the warbler's favorite prey in North
America, has been dropping. This is a more likely explanation of the warbler's decline.
Which of the following, if true, most seriously calls Scott's hypothesis into
question?

A. The numbers of the Baltimore oriole, a songbird that does not eat budworms but is as
dependent on South American coffee plantations as is the Tennessee warbler, are
declining.
B. The spruce-budworm population has dropped because of a disease that can infect
budworms but not Tennessee warblers.
C. The drop in the population of the spruce budworm is expected to be only temporary.
D. Many Tennessee warbler have begun migrating in the fall to places other than traditional
coffee plantations.
E. Although many North American songbirds have declined in numbers, no other species has
experienced as great a decline as has the Tennessee warbler

Experts please help
I am not able to find a suitable explanation for why the OA is what it is A instead of D.