Understanding Tiger Hybridization

Tigers in Our Backyard

Across the United States, tigers live amongst us in roadside menageries, exotic zoos, and cages in yards. With counts reaching as high as 10,000 throughout the country, this captive population outnumbers the dwindling number of tigers that roam freely in their natural habitat. As humans have fostered tigers in captivity over the past century, they have bred them to create unnatural hybrids, mixing species and creating individuals far distinct from their sub-speciated ancestors. So how did we get here? Who are these tigers? And what can we do to help conserve this critical species?

Tiger Subspecies in the Wild

There are currently 7 recognized subspecies of extant tigers, which are distributed throughout Asia. The Bengal tiger is the most common subspecies, found primarily in India and Bangladesh, while the Sumatran tiger is found only on the Indonesian island of Sumatra. The other subspecies include the Siberian (or Amur) tiger, Malayan tiger, and Indochinese tiger. All of these subspecies are either endangered or critically endangered due to habitat loss, poaching, and human-wildlife conflict. The South China tiger is functionally extinct, meaning it only lives in captivity, and not independently in the wild. The Caspian and Javan/Balinese tigers are completely extinct.

Tigers in Captivity

Tigers were first brought into captivity in the United States in the late 19th century, primarily for display in zoos and private collections. At that time, there was a great fascination with exotic animals, and they were indicators of wealth for individuals and institutions. However, in the 20th and 21st centuries, the reasons for keeping tigers in captivity expanded beyond display and exhibition. The trade of tiger parts, such as skins and bones, became a lucrative business, leading to an increase in the number of tigers kept in captivity for the purpose of producing these items.

Tigers were also used for entertainment, including in circuses and other shows, and have grown in popularity in recent years due to the boom of the popular Netflix show "Tiger King" and other pop culture sensationalizations of the species.

This long-term practice of tiger ownership has created a huge animal welfare issue, leading to the unnecessary death and torture of thousands of individuals, and a nightmare of inbreeding and genetic admixture.

At the end of 2022, the Biden Administration signed into law the Big Law Public Safety Act which aims to outlaw the illegal ownership, trade, and breeding of captive cats like tigers. This law has played a part in limiting the harm inflicted upon these animals in captivity, though the problem is still pervasive across the country and the world.

Hybridization of Species

As tigers have been bred in captivity, there has been a general disregard for sub-speciation in breeding regimens, creating unnatural hybrids of tigers. Not only are tigers bred across subspecies but they are bred with other big cats, most commonly lions. Ligers and tigons have grown in popularity in the US due to their huge size, mixture of stripes and spots, and exotic nature.

Genetic Profiles

The tigers that live in the US represent the many subspecies of tigers found across Asia. While there are some individuals that have maintained a pure bloodline within their respective subspecies, the majority are a mixture of many. This admixture has created individuals that represent several, if not all, known subspecies of the striped big cat. The graph shown below visualizes the variation in genetic representation of captive individuals, compared to purebred individuals.

These hybridized tigers present a unique challenge for management in the US, as they don't technically fit under the categories of conservation of the pure tiger subspecies. Before diving into the complex details of these tigers, let's meet a few of them.

While tiger hybridization and the creation of ligers/tigons may seem like a recent phenomenon in the United States, they are not the only animals that have experienced this unfortunate fate. Hybridization has been viewed by some as a potential conservation measure for ensuring the survival of endangered or near-extinct animals. This form of genetic rescue implies that subsequent populations would mostly be hybrids, creating controversy regarding an animal’s ability to qualify for protection under the Endangered Species Act (ESA). In this section, we will examine some case studies of hybridized mammals in the US, other than tigers.

ESA and Hybrid Ambiguity

Because the status of hybrids between species, subspecies, and populations was left unclear in the ESA, there has not yet been a systematic consensus across covered agencies on how to proceed with hybrid conservation situations beyond a case-by-case basis. The Fish and Wildlife Service (USFWS) has been a proponent of protecting hybrids while the Department of the Interior, as a whole, is against protecting them. Methodological approaches to the reality hybrids are necessary in order to better conserve wild tiger populations mixed with introduced subspecies and help prevent the trade and mistreatment of tigers in the United States.

Grey wolves

It is likely that grey wolves have mixed with domestic dogs, creating dog-wolf hybrids, and their unique identity combined with the ambiguity of the ESA regarding hybrids has complicated conservation management practices. While grey wolves are protected under the ESA, hybrids present genetic, evolutionary, and socioecological challenges and may not be eligible for protection.

"Cocktail Orangutans"

In an attempt to bolster reintroduction efforts in declining wild orangutan populations and care for confiscated animals, sanctuaries have inadvertently created an orangutan like no other. By collecting animals from different source populations-that have not been in genetic contact for significant periods of time-and allowing them to reproduce, these rescued orangutans may not be able to live in their native ranges. Similar to the plight of tiger hybrids, these "cocktail orangutans" may have a limited chance at life, but they are held captive within the United States, unable to return to their natural habitat. Continuing to intermix/interbreed tigers from separate populations without adequate policy to protect these tigers from being traded or taken from the wild will only exacerbate America's tiger problem.

Implications of Hybridization

GENETIC: Hybridization between different species of tigers can result in the dilution of unique genetic traits of each species. The preservation of genetic reserves through captive breeding programs is crucial for the long-term survival of endangered species, including tigers. Hybridization between different tiger species may undermine these efforts by introducing mixed genetics into the breeding pool, making it more challenging to maintain purebred populations and preserve each species' unique traits.

ETHICAL: Many (most) tiger "sanctuaries" which cross breed tigers provide inadequate living conditions, lack of proper veterinary care, and inappropriate social environments which can negatively impact the health and well-being of these animals. Moreover, these practices can also frequently support the illegal wildlife trade by creating a market for exotic pets and animal parts.

POLITICAL: The presence of hybrids can complicate effective management and legislation for the animals in question. These individuals may not be protected by laws designed for specific tiger subspecies. Cases of hybridization are rarely simple or clean-cut. It is difficult to design laws or policies sufficiently flexible to manage hybridized animals. Note, in 2022 the Big Cat Public Safety Act was passed restricting the ownership and display of tigers and other big cats.

CONSERVATION: The presence of hybrid tigers can complicate conservation efforts, as these individuals may not be protected by laws designed for specific tiger subspecies. Resources allocated for the conservation of purebred tigers might be diverted to managing hybrid individuals, potentially reducing the effectiveness of conservation programs.

In summary, the issue of tiger hybridization is pervasive across the US and causes a host of animal welfare, ethical, political, and conservation challenges. At this point, many cats are too far genetically disconnected from their wild relatives to play a role in reintroduction efforts, though with intentional management, captive breeding can play a role in conservation initiatives. In order to ensure a healthy future for the big cats in captivity and maintain the possibility for their involvement in the conservation of endangered wild tigers, more specific legislation will be necessary to regulate intermixed breeding for exotic entertainment purposes, along with stricter animal welfare laws to ensure humane care practices.

Learn more and contribute to the effort to advocate for the rescue and well-being of tigers (hybridized and purebred) across the United States!