Polar bears are declared "vulnerable" by the IUCN. Before going into the details of why polar bear populations are on the edge, let's have a look at the polar bears biology.
Polar bears are marine mammals whose main diet are seals, especially the ringed seal. To hunt the ringed seal they need the sea water to be frozen over as they mainly prey on the young seals that are not yet in the water but in little ice caves. Hence their habitats are on or close to the sea. There are 19 sub populations with about 2/3s of them in Canada.
Polar bears mate in late April/May. Since there are not always males around to mate, the female polar bear has a so-called "induced" ovulation. This means she only ovulates when there is enough stimulation through a present male. This clever biological trick prevents a waste of eggs. Male and female stay together for a few days, frequently mating...just to make sure...;-).
After the mating period they part and both continue to hunt for survival. At this point the fertile egg(s) do not yet develop, they "just stay put", another smart move of nature called delayed implantation. In September/October then, the female polar bear looks for a den. Depending on the area, they either dig their dens into snow drifts or, as on the more southerly situated Hudson Bay, they actually dig their dens into the soil. It is not uncommon that they reuse old dens.
Now the development of the fertilized eggs starts and the cubs are born usually in late December or early January. Most polar bears give birth to two cubs,
sometimes it's only one
and very rarely she gives birth to triplets.
The above image is from a trip a few years back. As you can see, the cub in the middle is significantly smaller. His or her chance of survival is slim...Scientists assume that depending on the body condition of the female an according number of cubs develop to assure the best possible survival rate of the cubs later on.
The cubs are born with closed eyes, a very thin layer of fur and almost immobile hind legs, weighing only about 500 grams, roughly a pound. Thanks to the high fat content of the polar bears milk though they grow rapidly and by the time they leave the den they are a very active bundle of 10 to 15 kg.
Once they exit the den for the first time, they usually stick a few days around the den to acclimate the cubs to their new environment. Then they head off to the Hudson Bay as the mom is by now super hungry. The Hudson Bay females are basically without food from September to March the following year, having given birth and nursing all the while.
At the milk bar
The cubs usually stay with their mom for about 2 1/2 years. In his book "Polar Bears" Ian Stirling writes that most of the Hudson Bay cubs only stay with mom for 1 1/2 years. They are not sure why, theories are that there are more seals to hunt so that even the smaller bears could possibly hunt or at least scavenge on whats left by older bears, or that the ice is softer due to a more southern location and even smaller bears would be heavy enough to break through the ice to get to the young seals.
The survival rate of the cubs seems to be somewhere between 43% and 65%.
Once the cubs leave mom, she might mate right away. Most females have their first cubs when they around 6 years. Male bears are mature at the same age, but since competition is strong, the males usually have to get older and stronger before they might get a chance to mate.
How do we know all this? A lot of data especially on newborns, their weight and appearance, are collected from zoos. All other research is painstakingly done by researchers in the field. As I experienced myself, working under these cold conditions is no easy task. And the area to cover is immense. With the help of monitoring collars, biologists and other researchers could trace a few animals and collect data this way. As you can see these collars are massive! As we photographed that female polar bear we had long discussions about these collars. Sure, from the photography standpoint they are a nuisance, and more importantly what is the bears opinion on that? Do we really need them?
Tough question...this is was the ICUN writes about it: "Although scientific studies have concluded that the long-term effects of capturing and collaring polar bears are minimal (Ramsay and Stirling 1986, Messier 2000, Thiemann et al. 2013, Rode et al. 2014a), some local groups nevertheless consider these techniques disrespectful or harmful to the animals. As a result, population inventory and ecological studies have been delayed or not permitted. On the other hand, alternative research techniques such as aerial surveys and genetic biopsy capture-recapture methods were designed and implemented. Reduced monitoring will constrain governments’ ability to assess sustainability of harvest especially if abundance is estimated from aerial surveys which cannot provide data on vital rates (Aars et al. 2009, Stapleton et al. 2014)"
We all have heard that polar bears are in peril. Some scientists are more optimistic than others but the consensus is clear, the populations are declining.
Global warming or climate change as you will, has probably the most negative influence on the polar bear population. For example, over the last 30 years the sea ice in the Hudson Bay has declined 22%, meaning the time the Hudson Bay is frozen and giving the polar bears access to their hunting grounds is 22% shorter than 30 years ago...resulting in a direct correlation decline of the Hudson Bay population of about the same 22%. Scientists estimate that polar bears need at least 7 months of arctic ice to sufficiently hunt. "An annual ice-free period of ≥5 months is likely to lead to extended fasting, which is predicted to lead to increased reproductive failure and starvation (Molnár et al. 2011, 2014a, Robbins et al. 2012b)."
Again different studies have different outcomes, but this threshold could be reached as soon as in the next thirty years.
With the climate change other problems are on the rise, too. Parasites and pathogens that were not able to survive before might now be able to get a hold on polar bears. Especially if these are already weakened by food scarcity.
Running from the chasing brother...
...ooops, not fast enough...;-)
An already existing problem is the pollution of our oceans. Most of the pollutants are lipophil, which in this case means they are binding to fat in the body. Disastrous for an animal whose main diet consists of fat, as many of these pollutants are known to cause disruption of the hormone regulation and suppress the immune system.
On top of this already present pollution, with the sea ice melting now also new possible pollution threats await the polar bear. Formerly inaccessible areas might be developed for pipelines etc and ship traffic might significantly increase, happily polluting away...
"Polar Bears are often attracted by the smells and sound associated with human activity. Polar Bears are known to ingest plastic, styrofoam, lead acid batteries, tin cans, oil, and other hazardous materials with lethal consequences in some cases (Lunn and Stirling 1985, Amstrup et al. 1989, Derocher and Stirling 1991). Another concern is that seals covered in oil may be a major source of oil to polar bears."
Sorry, I could have just shown you the images of these incredible and cute or lets say incredibly cute bears.
But I am on a mission, by raising awareness I want to help saving this planet and all it's incredible fauna and flora...
one image at a time!
"Polar Bears" by Ian Stirling , The University of Michigan Press, 2005
Polar Bears International
JoAnne Simerson, Animal Behavior Consultant