Polar bears evolved from a brown bear (Ursus arctos) ancestor 4-6 million years ago and they have undergone some very dramatic changes.

Polar bears evolved from a brown bear (Ursus arctos) ancestor 4-6 million years ago and they have undergone some very dramatic changes.

The obvious changes are color (polar bear fur is colorless and thus appears white), the claws are much more curved, sharper and shorter and evolved for the capture of prey, the feet are furred, the skull is narrower and longer (likely an adaption to hunting ringed seals that use breathing holes, and to pre-warm air), the molars are more carnivorous than brown bears, and importantly, polar bears remain active through the winter whereas brown bears hibernate – the only exception is pregnant female polar bears that den over winter to give birth and rear cubs.

From a behavioral perspective, polar bears use much larger areas – brown bears use an area up to ca. 1000 sq. km while polar bears can use 10 to 50 times larger areas. 

The very high energy diet of polar bears allows this difference in space use. The high energy diet of polar bears allows them to grown much larger than Arctic brown bears (2-3 times larger).  Polar bears have fewer cubs usually 1-2 while brown bears have 2-3 – polar bears only have 4 functional mammae reflecting their smaller litters while brown bears have 6 mammae (in mammals, there is an approximate “rule” that the female has 2 times the number of mammae as the “normal” litter size).

The Tehran Times had an interview with Professor Dr. Andrew E. Derocher from Department of Biological Sciences in the University of Alberta who also wrote the book of “Polar Bears, A complete guide to their biology and behavior”.

Below is the text of the interview:

Q: Why some of zoo polar bears are not as white as wild polar bears?

A: Polar bears can appear yellowish if dirty or have oils in their fur that oxidize. The whitest bears are those on the sea ice that are in and out of salt water. In the wild, the bears roll a lot on the ice and snow when they feed and are able to stay meticulously clean.

Q: Does the scientific name of polar bears (Ursus maritimus) refer to their ability of swimming?

A: Polar bears are very capable swimmers but while they should be considered as “marine mammals” but they are not like seals, whales, or sea otters that can spend all or most of their time in the water.  Polar bears prefer to be on the surface of the ice.  Mothers with small cubs in the spring (e.g., < 30 kg) will walk great distances to avoid taking cubs into the water as they risk hypothermia and death if they are forced to swim in cold water.

Q: How will Arctic warming and other threats affect them?

A: The best way to view changes in sea ice is simply as a habitat loss issue.  Sea ice is disappearing quickly and depending on the month you consider, the loss rates vary considerably but can reach about 1% per year. Of greatest concern is loss in the spring and autumn/winter and these rates have been slower. With 19 populations of polar bears, the changes are going to show up somewhat differently and at different times. The main changes we see are loss in body condition (fat stores) as bears are forced off the sea ice earlier.

This results in lower reproductive rates and lower survival (usually of the youngest and oldest bears in a population).  Ultimately, such changes result in population decline. We have seen declines clearly linked to sea ice loss in 2 populations (Western Hudson Bay and Southern Beaufort Sea) but we suspect such effects are ongoing in another 3-4 populations. Some populations, however, will do fine for some years to come.

When it comes to “other human activities” we are very concerned about the effects of pollution. Polar bears are at the top of the marine food chain and thus bioaccumulate pollutants. Most of the pollution is transported to the Arctic from more developed parts of the world. Industrial chemicals and pesticides occur at dangerous levels (e.g., PCBs, PBDE, PFOS, DDT, DDE, heavy metals like mercury). Some are increasing and some are decreasing but they affect hormone regulation, growth, behavior, survival, immune system and other systems – evidence varies on each of these “effects”.  Hormone and immune system effects are very clear.

Development in the Arctic is an ongoing concern – oil, gas, shipping, mining are all concerns that may affect populations.  We have, however, little information on actual impacts.

With respect to other threats – we are concerned about over-hunting but this is not a major concern as we can control it.  Some populations are likely being reduced due to excess harvest so there is work to be done on this point.  Poaching in Russia is a concern.

Q: Recent studies suggested that their immune system is weaker in polar bears with higher levels of PCBs. what are the burgeon techniques for measuring this pollutant?

A: There is good evidence for the effects of weaker immune systems in more polluted polar bears.  I was involved with these studies and the effects are clear.  We expected such negative effects because PCBs have been shown to have such effects in other species.  In reality, we don’t know for sure if it is PCBs or some other compound or break-down compound (polar bears can break down PCBs but the products are perhaps even more biologically active).  Conservatively, polar bears likely have 400 or more chemicals in their bodies that are of human origin. We study the pollution loads using polar bear fat biopsies (taken from living bears), from blood samples collected from live bears, and from milk samples.  Some studies are done on bears taken in harvest.

Overall, the consequences of a weaker immune system are unclear but likely cause mortality in some much polluted individuals and quite likely, reduced reproduction in other bears.

Q: Please tell me about new conservation methods and plans. How much satellite tags are useful to survey about a long distance traveler?

A: Satellite collars are used to monitor bears (usually adult females and sometimes young adults – not males as their necks are larger than their head and can’t wear a collar as they slip off). We follow bears for 1-3 years. The collars provide GPS locations to a satellite and then send us the data by e-mail. We get 6 locations per day per bear.  The positions are accurate to about 5 m. We examine habitat use (sea ice types using satellite imagery), movement rates, fidelity to an area, and use this information to examine behavior (dates on and dates off the sea ice – these are key metrics for understanding loss of sea ice). Some bears are far out on the ice but others are still near shore – we are not sure why this pattern has emerged. Thirty years ago, all bears were on the ice by mid-November in most years but the delay is a concern.