An ursid hybrid is an animal with parents from two different species or subspecies of the Ursidae (bear) family. Species and subspecies of bear known to have produced offspring with another bear species or subspecies include brown bears, black bears, grizzly bears and polar bears, all of which are members of the Ursus genus. Bears not included in Ursus, such as the Giant Panda, are probably unable to produce hybrids. Note all of the confirmed hybrids listed here have been in captivity (except Grizzly/Polar bear), but there are unconfirmed reports of hybrids in the wild.
A recent study by Kutschera and colleagues  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 & American black bear, (2) brown bear and polar bear, (3) American black bear and Asian black bear, (4) bears currently distributed in Asia (sloth bear, sun 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.
Brown bear/American 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 Charles 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),...
Intercontinental brown bear hybrids
Hybrids between the European brown bear and the grizzly bear (now considered to be a North American variety of brown bear rather than a separate species) have been bred in Cologne, Germany. See grizzly bear for taxonomy.
Brown bear/Polar bear hybrids
- Since 1874, at Halle, a series of successful matings of polar bears 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 bear/Brown bear hybrids are white at birth but later turn blue-brown or yellow-white.
- An adult polar bear/brown bear hybrid bred in the 19th Century is now displayed at the Rothschild Zoological Museum, Tring, England
- Crandall reported the first polar bear/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 some brown bears are more closely related to polar bears than they are to other brown bears. All the Ursinae species (i.e., all bears except the giant panda and the spectacled bear) appear able to crossbreed.
Kodiak bear/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. One hybrid was named Willy and grew into an immense specimen. 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 (circumpolar) brown 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.
- 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.
Grizzly bear/Polar bear hybrids
The Grizzly bear is now regarded by most taxonomists as a variety of brown bear, Ursus arctos horribilis.
- Clinton Hart Merriam, taxonomist of grizzly bears, described an animal killed in 1864 at Rendezvous Lake, Barren Grounds, Canada as "buffy whitish" with a golden brown muzzle. This is considered to be a natural hybrid between a grizzly bear and polar bear.
On April 16, 2006, a polar bear of unusual appearance was shot by a sports hunter on Banks Island in the Northwest Territories. DNA testing released May 11, 2006, proved the kill was a Grizzly/Polar Bear hybrid. This is thought to be the first recorded case of interbreeding in the wild. The bear was proven to have a polar mother and a grizzly father. The DNA testing also spared the hunter the C$1000 fine for killing a grizzly bear, as well as the risk of being imprisoned for up to a year. The hunter had bought a license to hunt polar bears; he did not have a license to hunt grizzly at that time.
The animal had dark rings around its eyes, similar to a panda's but not as wide. It also had remarkably long claws, a slight hump on its back, brown spots in its white coat, and a slightly indented face — the nasal "stop" between the eyes which polar bears lack. The guide leading the hunt, Roger Kuptana of Sachs Harbour in the Northwest Territories, was the first to note the oddities. Several names were suggested for this specimen. The Idaho hunter who killed it, Jim Martell, suggested polargrizz. The biologists of the Canadian Wildlife Service suggested grolar or pizzly, as well as nanulak, an elision of the Inuit nanuk (polar bear) and aklak (grizzly or brown bear). Both grolar and pizzly were used by the Canadian Broadcast Corporation in widely distributed stories.
Presently, though the mating seasons overlap, the polar bear's season begins slightly earlier than the grizzly bear's. A blog columnist for the Seattle Post-Intelligencer suggested that more hybrids may be seen as global warming progresses and alters normal mating periods. The Canadian Wildlife Service noted that grizzly-polar hybrids born of zoo matings have proven fertile.
Grizzly bears have been sighted in what is usually polar bear territory in the Western Arctic near the Beaufort Sea, Banks Island, Victoria Island, and Melville Island. A "light chocolate colored" bear, possibly a hybrid, is reported to have been seen with polar bears near Kugluktuk in western Nunavut.
Asiatic black bear hybrids
In 2005, a possible black bear/sun bear hybrid cub was captured in the Mekong River watershed of eastern Cambodia. The hybrid's mane was relatively slight, forming a crest on each side of the neck, as is typical in sun bears and some black bears. The appearance of its face was intermediate between that of the sun bear and the black bear, though its ears and large stout canines closely resembled those of the sun bear. Overall, the hybrid resembled an Asiatic black bear with an unusually glossy pelage and an unusual head.
In 2010, a male hybrid between an Asiatic black bear and a brown bear named Emma was taken from a bile farm and into the Animals Asia Foundation's China Moon Bear Rescue
Sloth bear hybrids
Hybrids have been produced between the sloth bear (Melursus ursinus) and the Malayan sun bear (Helarctos malayanus) at Tama Zoo in Tokyo, and also between the sloth bear (Melursus ursinus) and the Asiatic black bear (Ursus thibetanus, or Selenarctos thibetanus).
- Verena E Kutschera, Tobias Bidon, Frank Hailer, Julia L. Rodi, Steven R. Fain, Axel Janke (2014) Bears in a Forest of Gene Trees: Phylogenetic Inference Is Complicated by Incomplete Lineage Sorting and Gene Flow. Molecular Biology and Evolution 31(8): 2004–2017. doi:10.1093/molbev/msu186
- Frank Hailer, Verena E. Kutschera, Björn M. Hallström, Denise Klassert, Steven R. Fain, Jennifer A. Leonard, Ulfur Arnason, Axel Janke (2012): Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage. Science Vol. 336 no. 6079: 344-347. doi:10.1126/science.1216424
- Darwin, Charles (1868). The Variation of Animals and Plants under Domestication. Volume 2 (1st ed.). London: John Murray. p. 151. ISBN 1-4068-4250-8.
- Reed, Elizabeth C. (April 1970). "White tiger in my house". National Geographic 137 (4).
- "Hybrid bear shot dead in Canada". BBC News. May 13, 2006. Retrieved May 27, 2010.
- "Wild find: Half grizzly, half polar bear". msnbc.
- HISTORICAL REVIEW ON THE SPECTACLED BEAR CAPTIVE BREEDING IN VENEZUELA by Denis Alexander Torres
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- Scherren, H. (1907). "Some notes on hybrid bears". Proc. Zool. Soc. London: 431–435.
- Martin, P.L. 1876. "Ursus arctos and Ursus maritimus. On bastards between these species born in Nill's menagerie at Stuttgart." Zoologische Garten, 1876:20-22. [Zoologische Garten, 1877:135-136. *W. Stendell and E. von Martens, tom. cit., pp. 401–402.]
- ------. 1882. "On a hybrid between a male Ursus maritimus and a female Ursus arctos." Zoologische Garten, 1882:xxiii, 370.
- Kowalska, Z. 1962. "Intergeneric crossbreed of the brown bear Ursus arctos L., and the polar bear Thalarctos maritimus (Phipps)." Przeglad Zoologiczny, 6:230, 1 pl. [Polish with English summary.]
- ------. 1965. "Cross breeding between a female European brown bear and a male polar bear in Łódź Zoo." Przeglad Zoologiczny, 9:313-319. [Polish with English summary.]
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- Wurster-Hill, D.H. and Bush, M. 1980: The interrelationship of chromosome banding patterns in the giant panda (Ailuropoda melanoleuca), hybrid bear (Ursus middendorfi x Thalarctos maritimus), and other carnivores. Cytogenet. Cell Genet. 27:147-154.
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