I just recently became a member of the Doris Day Animal League. Checking out their website, I came across this page saying that they merged with the Humane Society in 2006.
The live link takes me to an announcement in 2006 about the merger. I also learned that the Humane Society merged with the Fund for Animals in 2005.
So now I'm a contributor and member of all three...without even realizing they were related!