For the time being, much of the unclaimed areas are an animal watchers dream. This will not last however. The lack of human interference from poisons, car accidents, and hunting has lead to an explosion in various populations. However, these rapid expansions often lead to overshooting the point of equilibrium, another crash, and a series of pendulum swings over decades as the environ makes it to a happy medium. Rats and mice certainly don't seem to be in decline, but at least their growth is leveling off compared to the early days of plentiful stocked refrigerators and neglected grain bins. Predators like hawks and cats are still on the rise.
Escaped Zoo Life:
Elephants roam Texas, and tiger stripes blend with the great grasslands of the Midwest. A surprising number of non-native animals can be found if one looks, though reports of such need to be taken with a grain of salt. Few zoos kept enough animals to make for any self sustaining populations - especially for the larger animals. Smaller animals that did have a decent sized grouping were often in enclosures that made escape very difficult. Even five years later, most zoos and aquariums are unpleasant places to visit - though in a few places, people tried to save or release what animals they could.
Somewhat distressingly, its often the larger predators that adapt well. Omnivorous bears can deal with most climates and find prey amongst the indigenous creatures.
As stated in the introduction, numbers are running on the high side at the moment. Crocodiles, alligators, snakes, bears, and wolves are all doing well, as are birds not thrown off by lights aircraft. Fortunately, even the newest generations are still rather fearful of humans, and don't tend to wander into urban areas since the easy food sources like garbage cans have long since been looted.
Only a small percentage of domestic creatures were able to escape their confines after their masters left or dies, but it was still more than enough. Most of the smaller breeds of dog didn't do so well, but, medium to large ones did, and are in fact a bit of a nuisance. They are far less afraid of humans than their wolf counterparts, more likely to to be found in formerly urban areas, and many of them have picked up various diseases from their surroundings. Frankly, many people consider the wisest course of action to avoid reanimates and shoot dogs on sight - if only for health reasons. Still, there are loyal mutts to be found, and they can b quite helpful as a means of transit and protection.
Although escaped pets are not very uncommon, certain farm animals seem to be almost completely gone. Many breeds of pigs, cows, chickens are quite rare. While most people don't give this much thought, its believed that the animal grade nano-vac used to replace the regiment of hormones and antibiotics needed for factory farm conditions is to blame. Remaining examples or caught wild species are kept in many outposts to help provide eggs and milk to feed the populace, and they are valuable trade if the scavengers can keep them alive.
Reanimates and the WildernessMost animals can't readily tell the difference between a normal human.and a reanimate. However, since the later tend to be rather simple minded don't tend to acknowledge warning signs, they do tend to suffer attrition from animal attacks. Conversely, animals rarely seem to be on the acceptable targets list for reanimates, though some of the more advanced types do seem to kill other creatures.