An ursid hybrid is an animal with parents from two different species or subspecies of the bear family (Ursidae). Species and subspecies of bear known to have produced offspring with another bear species or subspecies include American black bears, grizzly bears, and polar bears, all of which are members of the genus Ursus. Bears not included in Ursus, such as the giant panda, are expected to be unable to produce hybrids with other bears. The giant panda bear belongs to the genus Ailuropoda. A recent study found genetic evidence of multiple instances and species combinations where genetic material has passed the species boundary in bears (a process called introgression by geneticists). Specifically, species with evidence of past intermingling were (1) brown bear and American black bear, (2) brown bear and polar bear, (3) American black bear and Asian black bear. Overall, this study shows that evolution in the bear family (Ursidae) has not been strictly bifurcating, but instead showed complex evolutionary relationships. All the Ursinae species (i.e., all bears except the giant panda and the spectacled bear) appear able to crossbreed.
Brown × black bear hybrids
In 1859, a black bear and a European brown bear were bred together in the London Zoological Gardens, but the three cubs did not reach maturity. In The Variation of Animals and Plants Under Domestication Darwin noted:
In the nine-year Report it is stated that the bears had been seen in the Zoological Gardens to couple freely, but previously to 1848 most had rarely conceived. In the Reports published since this date three species have produced young (hybrids in one case), ... A bear shot in autumn 1986 in Alaska was thought by some to be a grizzly × black bear hybrid, due to its unusually large size and its proportionately larger braincase and skull. DNA testing was unable to determine whether it was a large American black bear or a grizzly bear.
Intercontinental brown bear hybrids Although Eurasian brown bears and North American Brown bears are isolated, they are listed as a single species, so technically mating between the two sub-species is not hybridization, even though it cannot possibly occur in the wild. However, cross-breeding between the European brown bear and the North American grizzly bear has occurred in Cologne, Germany.
Brown × polar bear hybrids
Since 1874, at Halle, a series of successful matings of polar and brown bears were made. Some of the hybrid offspring were exhibited by the London Zoological Society. The Halle hybrid bears proved to be fertile, both with one of the parent species and with one another. Polar × brown bear hybrids are white at birth but later turn blue-brown or yellow-white. An adult polar × brown bear hybrid bred in the 19th century is now displayed at the Rothschild Zoological Museum, Tring, England Crandall reported the first polar × brown bear crosses as occurring at a small zoo in Stuttgart, Germany in 1876 rather than Halle in 1874. A female European brown bear mated with a male polar bear resulting in twin cubs in 1876. Three further births were recorded. The young were fertile among themselves and when mated back to European brown bears and to polar bears. DNA studies indicate that the ABC Islands bears have mixed brown and polar bear ancestry. Irish bears were intermediate between the modern brown bear and modern polar bear. This suggests that the Irish bear interbred with archaic polar bears during the Pleistocene. The Irish bear is believed to have died out circa 1000–500 BC, due to habitat loss and hunting.
Kodiak × polar bear hybrids "Kodiak" or "Kodiak brown" is a term now applied to brown bears found in coastal regions of North America. In the far north, these bears feed on salmon and often attain especially large size. "Alaskan brown" is sometimes used for Alaskan bears, but the main distinction is how far the bear is found from the coast. "Grizzly bear" is the term used for the brown bear of the North American interior.
In 1936, a male polar bear accidentally got into an enclosure with a female Kodiak (Alaskan brown) bear at the U.S. National Zoo, resulting in three hybrid offspring. The hybrid offspring were fertile and able to breed successfully with each other, indicating that the two species of bear are closely related. The Kodiak is also considered by many to be a variant or subspecies of the basic Arctic brown bear. In 1943, Clara Helgason described a bear shot by hunters during her childhood. This was a large, off-white bear with hair all over his paws. The presence of hair on the bottom of the feet suggests it was not an unusually colored Kodiak brown bear, but a natural hybrid with a polar bear. In a 1970 National Geographic article Elizabeth C. Reed mentions being foster mother to 4 hybrid bear cubs from the National Zoological Park in Washington, where her husband was director.
Grizzly × polar bear hybrids
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