i came up with a POD for this for my own TL project. it actually has to do with a later invention of the cotton gin, which encourages tobacco as the main American cash crop instead of cotton (at least at first) and the butterfly effects from there mean that there isn't as much habitat loss and, as a result, the passenger pigeon (and the Carolina parakeet, for that matter) lose slightly fewer than IOTL and survive as endangered species. iirc, i also wrote in that there are some earlier conservation efforts which save them in the long run similarly to the American bison. notably, though, the passenger pigeons don't survive in such huge numbers as when they were hunted to extinction: iirc, they were actually far fewer in the pre-Columbian period and experienced a population boom after the Interchange. ITTL, after being saved from extinction, they return to their pre-Columbian numbers in equilibrium with mankind and the rest of the ecosystem, and are a shining example of a successful conservation movement alongside the bison (and several other animals which are extinct IOTL that survive ITTL, including the great auk and heath hen)