During after the people disappeared, many animals escaped from zoos and safari parks. Herds of feral cows, sheep, goats, camels and horses have also appeared in the plains after escaping from ranches and farms. Surprisingly, there are zebras, cape buffaloes, and other non-indigenous herbivores because they escaped from zoos, safari parks, and private collections after they were abandoned due to the Cold War and started feral populations. The gray wolf population have greatly recovered. The bison population has greatly expanded. The pronghorn population has done so as well.