Well, "willing to pay for warm fuzzies" is a bad way to put it IMO. There's limited amount of money available in the first place, if you care about birds rather than warm fuzzies that doesn't make you a billionaire.

The figures people would pay to save 2000, 20,000, or 200,000 birds were $80, $78 and $88 respectively, which oughtn't be so much that the utility of money for most WEIRD people would be significantly non-linear. (A much stronger effect IMO could be people taking --possibly subconsiously-- the “2000” or the “20,000” as evidence about the total population of that bird species.)