As the population of Polar bears is not easily re-populated due to the limited reproduction habits in the beasts, it is imparative that the cycle is uninterupted as much as possible. Humans harvest the bears for many reasons to include zooilogocal studies. Thus when harvesting the polar bear knowing what sex it is becomes an important issue.
It is more acceptable to harvest the males rather than the females for reasons around maintaining healthy populations of polar bears. It is noted that when we attempt to take just the males, females get abducted unintentionally. The greatest percent of females declined population is due to the hunting of the majestic bear.
To assure the acuracy of the sex of every specimine taken is to check the chromosomaol DNA. Without this method, the rate of incorrect sexing of the bears was around 13.7%. But the realality of why this sexing is so darn difficult is as follows;
The bears are very furry and this makes it difficult to see their sex organs. Unless the bear is drugged, it is to dangerous to "go poking around" if you will.
Watching the bear pee may help in telling its sex. The boy ears have a similar organ like that of a dog. So when he pees, the stream may appear to be coming from his belly, whereas in a girl bear it will appear to come from the tail area,...this is not always accurate. Along these same lines, checking for a wet patch of hair on the belly versus the tail end may help in the task.
Even when a bear is drugged, it can be difficult to determine sex. If a zoo keeper lifts the tail of a female and doesn't see a vulva, he may think the bear is a male (the vulva in female bears are very small if she is not in heat). When feeling around the belly for a penis, the small organ may be mistaken for a bellybutton, as polar bears have outies and the bears are generally very young when humans try to determine the sex.
Hope this helps,