Polar Bears - Data, Pictures and Videos

[GreenGrolar]

(10-21-2023, 01:24 PM)Spalea Wrote: @GreenGrolar 

About #257: something I don't understand in your interesting post... In the link you mentionned it is written: " However, polar bears have one big disadvantage: their skull morphology. Due to their flattened heads, the stress on a polar bear’s jaw bones is very high when biting at full force. Grizzly bears don’t have this problem, meaning that they can use the maximum bite force in a fight. "

It sounds like a bit contradictory to me... Due to their flattened heads, the polar bear aren't able to bite at full force... If it is really the case, polar bear aren't allowed to use their big bite force (bigger than the white shark's one), thus why these powerful jaw  muscles do exist if they must not to be used ? If a skull is made weaker by its flattened form, nature must reinforce it by an other way, because the nature abhors a vacuum and the useless. If the huge muscles of the polar bear jaws really exist, what are they for ? Correct me if I am wrong but the polar bear's skull bones are thick and huge, even when compared with the other bears ?

The comparaison with the white shark is timely. When a white shark bites a prey, it tears the flesh and, often in a case of huge prey, get away with a big piece of meat in its mouth. Nothing like it with a polar bear, like mostly mammalian predators it puts a pressure on the prey and maintains it in order to kill it (the prey). In this video, even if the polar bear is only killing a walrus cub we clearly see that it can put a pressure on its preys. So the question is: are you really sure that the polar bear's biting force is so strong ? 

Nevertheless it's not the first time I read something about the polar bear's submissive attitude when confronted in front of  a big brown bear. As if something, a limiting factor, prevented them to developp their full strenght potential.

The only bear which polar bears encounter in the wild are the barren ground grizzly (though I did post a video where a polar bear encountered an American black bear and scared it off - the video was in Churchill, somewhere on this thread). Polar bears are only submissive if they are not use to the grizzlies presence. There is one account of a polar bear actually defending its carcass from a grizzly and another account which states that older males are more composed around grizzlies than younger males.

Regarding polar bears not being able to bite at full force, I personally and respectfully disagree. Polar bears being able to bite (or rather slice) through the skin of belugas (which have skin 100 times thicker than that of land animals) shows that they have compensated crushing for slicing.

Anyway:

*This image is copyright of its original author

*This image is copyright of its original author

Saying a polar bear has jaws stronger than a great white shark refers to pound to pound. Off course a great white shark will be able to chew off way more flesh and have a much better slicing bite than the polar bear. A larger polar bear will have a stronger bite than a smaller grizzly overall but a weaker crushing bite pound to pound at least.

The polar bear's slicing bite exceeds that of all bears.

In addition:

Another significant difference between the species are their skulls, which, while similar in size, vary greatly in bite force and bone strength. The polar bear has a stronger bite, but a weaker skull. Polar bears are one of the most rapid instances of evolution in surviving species of animals, having evolved from the grizzly bear within the last five hundred thousand years. So why are their skulls weaker if their bite is stronger? 

Simply put: seals are easy to chew. Grizzlies are omnivores, as most bear species. Their diet subsists of salmon, elk, and small game, but includes a hefty amount of vegetation. Polar Bears, in the ice and cold, were forced to eat seals (as well as penguins, fish, even belugas). Seals are largely blubber, providing the caloric intake necessary to sustain these large beasts, but offering little resistance in the chewing process. 

*This image is copyright of its original author

Skulls of the polar (left) and grizzly bear (right). Modified from P. Christiansen, Journal of Zoology (2006).

https://beargorillarealm.proboards.com/thread/37/polar-collection-excluding-weight-predation?page=1&scrollTo=632

Regarding the info you quoted from the same link:

Polar bears are the strongest bear species. Their bite force of 1,235 PSI is more powerful than that of a Bengal tiger and about eight times stronger than that of a human. In addition to a strong bite, polar bears also have a paw swipe force of over 1,800 pounds. That’s five times stronger than the punch force of a human. 

How Strong Are Polar Bears’ Jaws?
Polar bears have the most powerful bite force of all bears, their jaw strength reaching 1,235 PSI. However, their skulls are structurally weaker than the skulls of grizzly and brown bears, giving the latter an advantage in a head-to-head fight.
Compared to other bear species, polar bears have low, flat skulls that are thinner than the skulls of grizzly or brown bears. This morphology is the result of evolution and adaptation to the marine and arctic environment, allowing polar bears to increase hunting efficiency by thrusting their heads into seal breathing holes in the ice. 
However, this shape increases the stress on the jaw bones when biting. For this reason, polar bears feed almost exclusively on young prey that is comparatively smaller than their own size and weight.

From sentences highlighted and underlined are from the same source as the words in italic (also in your post).

My opinion: The info saying that the yellowish white bear will lose in a fight is not wrong but misleading. A polar bear will lose to a brown bear or grizzly in a head to head fight is wrong unless they are close in weights. Only the Peninsula Alaskan grizzly bear and kodiak bear overlaps in weight with the polar bears population from Svalbard and the average polar bear population respectively.

Male polar bears from Foxe Basin will outweigh kodiak bears by a decent weight advantage and the average male polar bear outweighs a Peninsula Alaskan brown bear at average weights too. Polar bears feed on young prey smaller than themselves almost exclusively is wrong as 25% of their diet consist of prey other than ringed seals which are bearded seals (which can outweigh a female polar bear), belugas, narwhals, and walruses.

Although a polar bear can bite through the skin of a walrus, it is protected by thick hide and blubber (protecting its vitals) allowing it to escape into the sea on time.

More accounts in the link below:

https://beargorillarealm.proboards.com/thread/15/polar-bear-predation?page=1

Here is one example:

*This image is copyright of its original author

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