I spent a good amount of time last month looking at birding demographics. Here's a chart showing to scale various birding populations in the United States (click to enlarge).
There are various ways to calculate both Audubon and American Birding Association membership, so these should be taken as rough estimates. Either way, you can see that membership in these bird organizations is very small compared to the number of people that are interested in birds, or regularly birding. With 2.4 million adult Americans keeping a life list of birds seen, ABA has huge growth potential just targeting these people.
How does birding membership compare with other groups? Well, there are reportedly 1.1 million duck hunters in the United States. How many of them are members of Ducks Unlimited? 608,154. Over half of all duck hunters are DU members! So, what are the differences between birders and hunters that make it so that half of all duck hunters will join DU, but only a tiny fraction of birders will join ABA? Alternatively, what is it that DU provides its constituency, that ABA isn't providing right now for birders?
Can you imagine an ABA with 500,000 members? Imagine what we could accomplish if 500,000 birders were united in fun and the protection of the wild birds we enjoy!