In this scenario, all the humans on earth have disappeared, except for Fred. Sure, Fred is sad that everyone that exists is dead but him, including his friends and family, but he doesn't let that get him down in the dumps. What did get the former PETA supporter, Fred, sad was all the zoo critters. So he hopped in his car and trucked across America to free the zoo animals. Foolishly though, after freeing them, he was eaten by a lion.

Now that Fred has freed all the zoo animals in America (don't concern yourself with how he did this), did he accomplish anything? Would the animals commonly kept in zoos, such as lions, chimps or hippos even be able to survive in an environment so different from their own?

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    $\begingroup$ I mean some zoos have deer and there's a friggin plague of them in my neighborhood eating my squash, so I'm going with deer. $\endgroup$ – kingledion Dec 9 '16 at 7:29
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    $\begingroup$ North America is a big place. A lion will have a better time of it in, say, Mexico as in Calgary. And zoos keep a lot of animals. I fear this question is too broad. America is an even bigger place. Do you mean the United States (still too big)? $\endgroup$ – Schwern Dec 9 '16 at 7:50
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    $\begingroup$ There's probably a huge variety of animals already out there happily living and breeding in places they shouldn't. Escobar's Hippos, Pelicans in London's parks, wallabies in the UK. Obviously pack/herd animals would cope better with freedom than lone predators. Well, predators would be able to eat, but probably won't find mates. $\endgroup$ – user10945 Dec 9 '16 at 7:59
  • $\begingroup$ @Pete, most of the big predators are kept in mating pairs/groups in the hope that they will. At least at respectable zoos $\endgroup$ – Separatrix Dec 9 '16 at 8:01
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    $\begingroup$ @Separatrix - Lions maybe, as they're pride animals. Leopards, Cheetahs etc. tend to hunt alone, and seek mates when they get broody (and don't tolerate each other in non-breeding times). This requires a certain concentration of suitable mates within an area though. $\endgroup$ – user10945 Dec 9 '16 at 8:11

Because "America" is an enormous and diverse place spanning pretty much every biome, and because zoos contain dozens and dozens of different animals, I'm going to narrow this down to the Oregon Zoo here in my hometown of Portland, Oregon. Here's their list of animals and some information about their habitats.

Since their main threat, humans, are gone, the question of survival is mostly one of habitat, food and predators. The area around Portland has very diverse climate and terrain and it rarely freezes (he writes while there's snow outside) which gives the animals a good chance. Portland is also a fairly small city geographically, the zoo is at the edge, and it's surrounded by large amounts of forest, so the animals have a good chance of blundering their way into wilderness. In contrast, animals released from the Bronx Zoo will probably never made it out of the concrete and suburban jungle that is the Northeast Corridor.

On the other hand, for the animals described as "tropical" or "sub-Saharan" or "desert" are probably screwed.

I'm not going through the whole list, just A and B to give you an idea.

Won't Survive The Winter

  • African bullfrog
  • African lungfish
  • African red-billed hornbill
  • African rock python
  • African slender-snouted crocodile
  • African spurred tortoise
  • Allen's swamp monkey
  • Arrau turtle
  • Black crake
  • Black rhinoceros
  • Blue and gold macaw
  • Blue-streaked lory
  • Burmese python

Might Be OK

  • African crested porcupine
  • African pygmy hedgehog
  • African wild dog
  • Asian elephant
  • Australian walking stick
  • Black howler monkey
  • Bontebok
  • Bull trout (the Willamette River is probably too polluted)

Just Fine

  • American beaver
  • American black bear
  • Amur leopard
  • Amur tiger
  • Bald eagle
  • Bobcat
  • Bufflehead
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    $\begingroup$ The Blue and Gold Macaws might be okay, there are several instance of escaped wild parrots becoming feral populations in places you might not expect. London has a population of feral parakeets.en.m.wikipedia.org/wiki/Kingston_parakeets. In this scenario of course humans will be gone so perhaps there is less feeding opportunities. $\endgroup$ – Sarriesfan Dec 9 '16 at 12:42
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    $\begingroup$ Black Rhinos won't survive the winter? You live in Portland, man, not Chicago. $\endgroup$ – kingledion Dec 9 '16 at 14:52
  • $\begingroup$ @kingledion Portland is well outside a rhino's natural range. Black rhinos range from equatorial Africa to South Africa. Cape Town is a full 10 degrees of latitude closer to the equator than Portland and is 5C warmer in winter. It's snowing right now. $\endgroup$ – Schwern Dec 9 '16 at 19:47
  • $\begingroup$ I thought (prehistoric) humans were a contender for the extinction of the native rhinos. $\endgroup$ – user25818 Dec 9 '16 at 23:45
  • $\begingroup$ @notstoreboughtdirt Yes, we are, probably plus desertification of North Africa. But they've never ranged outside the tropical zone. See en.wikipedia.org/wiki/Rhinoceros#/media/…. The solid colors are the rhino's current range and the outlines are its historical ones. $\endgroup$ – Schwern Dec 9 '16 at 23:57

Generally speaking small animals have a higher chance of survival than big ones because they need less food to go through winter.

A lion needs to eat every week. I m not sure how they would catch prey every week in a cold winter.

Animals whose habitats are extremely different from America (polar bears, african giraffe) will probably struggle.

Then there is the question of reproduction. Even if your 4 african leopards can survive America's climate, if they don't stick together all the time (they don't), the chances of them meeting another leopard are quite low. Thus they would go extinct.

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    $\begingroup$ Insects and small animals that can breed in huge numbers would be the biggest contenders. Some zoos keep a population of feeder animals those might be the biggest concern. $\endgroup$ – John Dec 13 '16 at 4:33
  • $\begingroup$ African animals, particularly South African ones, might do just fine in the warm and semi-arid parts of the US Southwest, assuming they could eat what's there. Whereas polar bears might do fine in Maine which isn't too far from their natural habitat of Newfoundland. This is the problem with asking about "America" (by which I think the OP means the United States) because it's such a large area with a diverse series of biomes. $\endgroup$ – Schwern Dec 13 '16 at 4:35

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