The Humane Society rescued these tigers from a roadside zoo in Missouri and had them moved to a legitimate sanctuary (with more space and better fences) in Cleveland. Kathy Milani/The Humane Society of the United States via AP Images

According to the latest estimates, there are approximately 3,890 tigers left in the wild, but experts say that there are more than that in captivity in the US alone.

In fact, Carson Barylak, who heads the "Big Cats in Captivity" campaign for the International Fund for Animal Welfare (IFAW), tells Tech Insider that they estimate there are more than 10,000 tigers in backyards, basements, pseudo-sanctuaries, and roadside zoos around the country.

It's hard to estimate exactly how many captive tigers there are in the US since there's no central registry tracking them, a spokesperson for the Association of Zoos and Aquariums tells Tech Insider, but "it is certainly plausible that there are more tigers held in human care in the United States than remain in the wild." There are fewer than 350 tigers in AZA-accredited facilities, which are legitimate zoos involved in conservation.

A spokesperson for the US Fish and Wildlife Service tells Tech Insider that they have a similar estimate of more than 10,000 tigers held all over the US.

Where the captive tigers are

The vast majority of these animals are in places that aren't certified by the AZA or the Global Federation of Animal Sanctuaries. And when we say that these animals are frequently kept in backyards and even basements, that's no exaggeration. The basic requirements that dictate what people do with their exotic animals, especially in some states, are minimal.

For the most part, these non-AZA and non-GFAS accredited sites are not good places for these animals to be. Most private owners, even those who care about and want to rescue these animals, can't provide the care, space, and environment that they need, a situation that can end in disaster.

Places like JNK's Call of the Wild Sanctuary, a defunct facility that authorities seized 19 exotic animals from, exist (in this case, until recently) even in theoretically highly regulated states like New York. The Zanesville, Ohio, disaster that resulted in the deaths of 18 tigers, 17 lions, eight bears, three cougars, two wolves, one baboon, and one macaque, happened when a man killed himself after releasing those animals — which all lived in his backyard.

When responding to a flood disaster in the US, Gail A'Brunzo, wildlife-rescue manager for IFAW, tells Tech Insider that a a group of first responders were going door to door when one opened a basement to find "a huge tiger ready to pounce on him."

"That responder could have been torn apart," A'Brunzo says.

Many of the roadside zoos that are homes to these cats meet a bare minimum of standards required by the USDA that many experts don't consider sufficient for safe and humane treatment.

The big cats around the country are mostly tigers, according to Barylak, with a good number of lions, plus smaller groups of cougars, leopards, and others.

A tranquilized lion that's being removed from a defunct sanctuary is iced down to lower his body temperature. IFAW - International Fund For Animal Welfare/YouTube

Both the International Fund for Animal Welfare and the Fish and Wildlife Service stress that the 10,000 estimate is just an estimate, since there's not a full record of which exotic animals are being kept by exhibitors or private owners in any location. Facilities are supposed to keep records of animals that come into and out of their possession, but the USDA hasn't made copies or kept those records themselves (new FWS regulations require permits for interstate trade as of April 2016).

That 10,000 number is actually a conservative estimate, Barylak says, one that was calculated based on analyses of how many private facilities and owners are out there, along with a look at the number of sites that breed big cats.

It doesn't include animals at zoos accredited by the Association of Zoos and Aquariums, and it doesn't count big cats at good rescues or sanctuaries (those that don't allow direct contact with animals and don't breed them) — it's just the number of animals that are privately owned.

What the law says about pet tigers

So why do we make it so easy for people to own animals that aren't domesticated and are dangerous? In general, experts say, there's no conservation value in having private individuals breed these animals. Legitimate zoos and research programs have detailed plans for doing that.

People who breed these animals to display them or to let people handle cubs aren't "saving" them, they're profiting, and creating a population of animals that there's no safe and good place for.

Skye Gould/Tech Insider

Animal rights groups want legislative changes that essentially prohibit private buying, selling, and breeding of these animals. An AZA spokesperson tells Tech Insider that they "have fought for legislation on the federal and state level to restrict who can own exotic animals," and they do not think exotic animals make good pets.

Advocates say that one key part of eliminating the private tiger trade is an effort to make it illegal to handle tiger cubs, something the USDA now allows while the cubs are approximately between eight and 12 weeks old. To work within that short time window, facilities that regularly offer cub-handling to visitors must continually breed animals. This worsens the situation considerably.

"Private breeders like cub handling businesses essentially produce as much of their 'product' as they can because cubs = cash," Barylak tells Tech Insider in a follow-up email.

There are some hopeful legal changes. The new FWS regulations mean all tiger sales that cross state lines will require permits. Until now, "generic" tigers (not part of a particular subspecies and not considered valuable for conservation) were exempt from those permits — and the vast majority of these captive tigers are generic.

The USDA is stepping up too. In March of 2016, the USDA announced that letting members of the public handle exotic animal cubs that were under four weeks of age — when they need to be with their mothers and are particularly vulnerable to disease — violated the Animal Welfare Act.

Still, these legal changes will continue to allow exotic cubs to be sold without permits as long as they don't cross state lines. And slightly older cubs can still be handled, even if there are more regulations governing that process.

Years from now, there may be even more than 10,000 tigers in captivity in the US — due primarily to that constant breeding required by operations that make a profit by offering up a steady supply of tiger cubs to largely oblivious visitors.

"If I had to call somebody the bad guys, that's who it would be," says Barylak, referring to the breeders who offer cub-handling. "They know what they are doing."