Re: the DONOR & VOLUNTEER ADVISORY stating "This organization's nonprofit status may have been revoked or it may have merged with another organization or ceased operations."
That statement may be because this organization that supports the Saint Louis Zoo is now known as the "Saint Louis Zoo Association." (I believe the EIN has also been changed).
I fondly remember the many, many trips my mom Frances and I would take during the summers of my boyhood by public transportation from our home in Old North St. Louis to the zoo. Back then (the late 1950s/early 1960s), the zoo was more about entertainment then education (as was true of most zoos back then) and while the animal enclosures would allow you to get "up close and personal" with many of the animals, they were really not the best for the animals' wellbeing.
A lot has changed since then, and today the Zoo's animals enjoy much more roomy and natural habitats and the Zoo emphasizes educating people on the perilous state many animals find themselves in in the wild. The Saint Louis Zoo is one of the most consistently highly rated and popular zoos in the USA and (unusual for a zoo of its caliber, admission is FREE). While it receives taxpayer funding, it relies heavily on individual contributors and the Saint Louis Zoo Association is a nonprofit organization that provides much needed support.