I came across this article, which details the breeding of hybrid bears at the Smithsonian National Zoo: https://www.washingtonpost.com/loca...85fcc2-5fde-11ea-b014-4fafa866bb81_story.html The National Zoo’s first hybrid cubs — twins — were born in 1935. One hybrid cub lived 15 days before it was found outside the den, frozen to death. The other disappeared and was believed to have been eaten by Ramona. The following year, Ramona gave birth to four more hybrid cubs. If they survived, The Post proclaimed, they would be “a biological rarity on par with the Dionne quintuplets.” One of the cubs died, but in May 1936, the three survivors were deemed healthy enough to make their debut before a jostling crowd of newsreel photographers. Two more hybrid bears were born in 1939, one of which — Willie — survived into adulthood. That gave the National Zoo four of the genetic anomalies. But it’s what happened next that really stunned the zoo world: In 1950 Pokodiak gave birth to a litter of cubs. The father was her brother, Willie. This was unexpected. Hybrids are typically sterile, such as the mules that result from a horse/donkey pairing. One cub survived: Gene, short for “genetics.” Its photo graced the cover of the Journal of Heredity. Out of more than a dozen hybrid cubs born to hybrid parents at the National Zoo, Gene was apparently the only one to live to adulthood. The rest couldn’t overcome their aberrant DNA. Click on the above link to read the full article. It’s interesting to note their amazement at the production of a fertile hybrid. It would now be easy to name several examples of fertile hybrids e.g. female Tigons. It was also strange to hear of a Polar bear as the parent of a litter of four cubs. Although he was the sire, with the litter size largely determined by the mother (he only had to fertilise the eggs); it still highlighted the difference in litter size between these two species. Litter of three to five in Kodiak bears are not uncommon; but in Polar bears - litter of two make up 70% of births; litters of one make up 25-30% of births and triplets or quadruplets are highly unusual.
I guess it goes to show that, back then, keepers were simply laborers, not the behaviorists and reproductive experts they are today. The most important things for cubs or pups is WARMTH. Maintaining body temperature is crucial, so the caloric value of milk could be put toward growth, not maintaining temperature. If milk has to continue to go toward thermal needs, the animal becomes a "poor doer" and can't thrive or survive. It seems a pretty elementary requirement to heat the den and make sure the cubs remained in the den snuggled against mom. It's inconceivable to me that keepers didn't notice the dead cub for quite a few days, by which time it was frozen. The hybridization is not as much a miracle here as any of the 12 cubs surviving with this kind of keeper indifference. If cubs are abnormal in some way, mothers can know. They will consume the cub to prevent predators from finding any traces of it and sending their are other young prey around. This instinct is so strong it remains even in domesticated dogs.
I think this is more a case of the management methods of the time, coupled with the shortcomings in enclosure design. Many bear cubs born in those days didn't survive because of disturbance to the mother in their early days. Remember there were no surveillance cameras available in those days with which to monitor events in the cubbing den from a distance. Instead, when cubs were born, keeper policy was likely to keep well away and not interfere at all etc. This meant no cleaning out, no noise or close observation or contact. As long as the cubs could be heard, all was presumed well. This was certainly the policy in the early successful births of Polar bear cubs in the UK in the 1950-60's era. I don't see any reference to the 'frozen' cub not being discovered for 'several days'. It may well have been ejected outside by the mother, or crawled out by its own, where it was then discovered dead the next morning.. The scientific importance of these breedings was that they proved a much closer link between Polar and Brown bears than was previously assumed. Though I imagine that the low survival rate was due more to the shortcomings in management/denning facilities than their 'aberrant DNA'.
This makes perfect sense. I'm pretty sure Polar X Brown (of any race) hybrids have proved totally viable as individuals, and fertile breeders inter se and with either parent species, where management systems have been conducive. Genetically the species are pretty close.
Apart from these Washington births, I am not sure how often this cross has been repeated though, but Polar and Brown bears have often been kept together- Flamingo Park in Yorkshire for a long time had a mixed bear exhibit- several species including Polar and Brown were involved.
Hasn't this cross occurred in the wild on occasion? I remember reading about hybrid PolarXGrizzly Bears in Alaska some years ago. ~Thylo
Yes, Grizzly x Polar Bear hybrids (called Pizzly Bears) occur in the wild in Alaska occasionally. EDIT: Cross-posted with Pertinax.
Crandall records Polar X European Brown Bear hybrids reared in Stuttgart in 1876, which apparently bred freely with each other and with the parent species. There is a relatively recent case of this happening some where in (Eastern?) Europe. The animals are probably still alive. Mixed bear exhibits used to be common, certainly Bristol had one in the 1970s, although Polar Bears were kept separate. A possible reason for no hybrids being reared in mixed groups is that, unless pregnant females were identified and isolated, any cubs would have quickly been 'recycled' by group members. Looks like there is a male Polar X Brown Bear at Osnabruck. His sister was shot after escaping in 2017.
I remember Bristol's 'bear terrace' well. The Polars in the original enclosure at one end, then the two newer pits. The one nearest the road entrance had a pair of Brown Bears. The bigger/longer one had three species I think- Sloth, Himalayan and Sun Bear. London had a similar mixed bear exhibit in the same era.
This was really my point, perhaps poorly stated. Keepers didn't really have the same function, and zoos let animals do what they do naturally. I think it's like that your scenario of the cub being ejected from the den is probable. If Mom suspected something was wrong with the second, she probably did with the first. I can't access it right now, but seem to remember something like "where it was finally found after 15 days " The important thing is that climate change is driving the ranges of these two species together, and it is predicted that this cross will occur more and more frequently. Since they are so similar, I too doubt the "aberrant DNA."
Indeed there are several records of polar bear X brown bear hybrids living into their late thirties. Two of the hybrids, born in the Smithsonian (Washington) Zoo in 1936, were still alive in the early 1970s. In her book Mammalian Hybrids (1972) Annie P. Gray lists a number of references appertaining to instances of polar bear X brown bear hybrids. I believe that the polar bear X brown bear hybrid, displayed in the Tring Zoological Museum, is one of these Stuttgart born hybrids.
This is true, there was a mixed bear exhibit since 1980 with European brown bears, polar bears, American black bears and a moon bear. Nothing ever happened until a brown bear mated with a male polar bear. 1.1 hybrids were born in 2004. They stopped the mixed bear enclosure right after. The siblings lived together until the tragic accident with the female that had to be shot after escaping in 2017. The male is still alive, shares the enclosure with silver foxes.
