Polar Bears - Data, Pictures and Videos

[sanjay]

Well, here we have another very in depth explanation of interaction between Polar bear and Brown Bear by Dr. Thea Bechshoft, Please take some time to read it carefully.

Question: Val, Jannicke, and Lauge have all been asking me about the relationship between polar bears and brown bears - are the two bear species closely related and do they mate?

Answer by Dr. Thea Bechshoft:
Yes, polar bears and brown bears are closely related. Exactly how close is a harder question to answer though!

There is only one species of brown bear, even if it is sometimes known under other names such as grizzly bear, Kodiak bear or spirit bear. Likewise, there is only one species of polar bear. Both of these bear species have a common ancestor that they evolved from. However, although some studies suggest that the evolutionary split that lead to the brown bear and the polar bear being two separate species may have happened as far back as 4-5 million years ago, there is still disagreement as to when exactly the split happened. Historically, both bear species inhabited an enormous geographical range. Because the split happened at different times in the different areas, the DNA results vary depending on which area and what time period is investigated - 10 million years ago in Siberia, 1 million years ago in Scandinavia, 1 thousand years ago in Greenland, or 10 years ago in Canada: each study is likely to give you a somewhat different answer.

Despite being two different species, polar bears and brown bears can still breed with each other, and even produce fertile offspring. A few zoos interbred the two bear species (a long time ago, before animal ethics was really something most people cared about), but now we mainly see crossbreeding between the two species because of climate change:

Polar bears are nothing without sea ice and seals, and so their range, historically and now, have been continuously diminishing as the ice has retreated northwards. However, the exact opposite is true for the brown bears: their food (plants, insects, small animals) has moved north as the climate has gotten milder, and so the brown bears have started moving further north too, into what is otherwise considered polar bear territory.

In other words, one of the current consequences of climate change is that polar bears and brown bears may actually meet more often than they used to. However, although polar bears and brown bears are each other’s closest relatives, their biology is sufficiently different that they only meet under relatively specific circumstances. Polar bears are specialized to living on the sea ice and hunting seals. When/if they are forced to stay on land they are basically starving while waiting for the sea ice to re-form. Grizzlies, on the other hand, are specialized to living on land, eating a largely vegetarian diet (and hibernating during the winter months). During spring or summer, however, the two bear species may meet where land meets ocean, e.g. scavenging for anything edible that may have washed up along the shore. Every now and then these encounters will be romantic in nature, resulting in what is known as “grolar” or “pizzly” polar bear/grizzly hybrid cubs.

Based on what has been observed in the field so far such cubs generally seem to have a polar bear mother and a grizzly father. This means that the cubs will be raised as polar bears, and thus be highly likely to mate with a polar bear once they themselves reach reproductive age. In other words - under the current climate - the grizzly DNA will (over generations) disappear from the bloodline.
A few stories have been in the news lately on how the interactions between the bears (in Canada) are changing:
http://www.cbc.ca/news/canada/manitoba/g...-1.3118936 and http://www.polarbearsinternational.org/n...-territory

If you go online to look at pictures of polar bear/grizzly bear hybrids, remember that grizzly bears can be any color between dark brown and light beige, a fact which seems to have confused quite a few of those who’ve posted pictures on various websites. A lot of pictures I've seen labeled as hybrids are not. For examples of how a grolar may actually look, see here:

*This image is copyright of its original author

*This image is copyright of its original author

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