I hate that graph. Not only is it not zero-based, a common mistake made by amateurs and people trying to mislead, but you can't even tell where zero is, even though the author of the graph clearly must know. They tell us in the text that 3 billion is one-third of the total. But if you didn't already know that, the graph would be meaningless. Suppose the total number of birds in 1970 was 3 trillion. Then the loss would be a tenth of a percent, which is negligible. You just can't tell by looking at that stupid graph.