The Decline in Approximately 70% of the World's Bird Species

Multiple Choice

The decline in approximately 70% of the world's bird species is particularly alarming to scientists because

A) This is the first time any bird species have been threatened with declining numbers.
B) It is not caused by any human activities that scientists can determine.
C) Only land birds are affected, while water birds seem to be maintaining normal population numbers.
D) Birds are excellent environmental indicators.
E) Birdwatching now generates a significant portion of tourist dollars in some countries.