I don’t think they were there at the beginning, but imagine the zoo wouldn’t have wanted them in recent years as a potentially invasive species…….there was a similar colony at Banham, which I think may have extended outside the grounds…..Prairie dog were kept at the “top end” of the zoo, and were found within the American bison paddock behind the penguins. I’m not sure if they were one of the zoo’s original “free-roaming” species nor do I know what their maximum number were. I personally don’t recall seeing them in any of the recent guidebooks either. They were pretty much left to their own devices! They certainly complemented the bison nicely as a mixed exhibit