Open water is appearing as the sea ice breaks up and begins melting. I took this photo from our helicopter yesterday, about twenty miles north of the Arctic coastline.

Polar bears mate in the spring. Females undergo delayed implantation; the fertilized egg does not implant into the wall of the uterus and begin development until autumn. Delayed implantation is unusual, but a surprisingly large number of mammal species do it. Despite much research, there is no consensus on the function of delayed implantation. Pregnant female polar bears dig dens in snow (and in some parts of the Arctic, into earth) in the fall then spend the winter in the den. They give birth to young sometime in December-January then the entire family emerges from the den in the spring.

This little bear is known as a C.O.Y. for “cub of the year.” Most of the COYs we have caught weigh around thirty pounds, and are still nursing. Usually, they will remain with their mothers until they are just over 2 years old, when they become independent. At this capture we have anesthetized both the mother and, with a very light dose, the cub; that is why the tip of his tongue is sticking out.

This is a one year-old that is still with its mother; it weighs 220 lbs. Around this time next year, it should become independent.

Research published in 2007 found that the subunit of polar bears in western Hudson Bay was a declining population. There are many mechanisms that can lead to population decline; in western Hudson Bay, survival of very young and very old polar bears has fallen over about the last 20 years, in concert with an advancing date of sea ice breakup in the spring. It is unknown exactly how sea ice decline affects polar bears, although it is likely that poorer ice conditions reduces the ability of bears to hunt. A goal of our project is to track changes in the physiology of polar bears during the summer, with particular attention to how changes may be affected by declining sea ice. This will help us understand why the western Hudson Bay population is declining, and how other subunits may be affected.

As the warm weather continues, we also have clear skies and good visibility, so we have been getting out for a lot of captures. Very long days – typically we fly out in the morning, perform captures throughout the day, then finish up lab work around midnight – but we are getting a lot of great data.

Nineteen of these subunits are populations of several hundred to several thousand bears; the 20th subunit is the Arctic basin, the area surrounding the geographic North Pole. Bears have been observed almost all the way north to the pole, but it is unknown if any bears are actually residents there. You can see a map of the subunits at this website: http://pbsg.npolar.no/en/status/population-map.html.

Some of the most well-studied polar bears are in western Hudson Bay, where bears come ashore near Churchill, Canada, during the fall months. Bears in the southern Beaufort Sea are also well-studied – this is the subunit of bears on which we are focusing. It is difficult to study what may be the most mobile mammal on earth; in some areas polar bears have home ranges over 500,000 sq km. Because bears move over such a large area and because they travel on variable sea ice, they are difficult to trap. Instead, finding and darting bears from a low-flying helicopter is the most common capture method.

We are using this helicopter this spring as a platform from which to dart bears. The pilot maneuvers the helicopter low and close to the bear, then a gunner leans out the window on the far side and uses a specialized firearm to shoot a dart into the bear. The dart contains a drug that immobilizes the animal and puts them under anesthesia. Here, the helicopter is parked in front of the lab with covers over the engine and the base of the rotors; space heaters beneath the covers keep critical components warm enough to start in the morning.

We are using this helicopter to aid in spotting bears, and to carry personnel and gear. It is smaller than the darting helicopter. The white tank attached to the belly is an extra fuel tank, giving us an additional 30 minutes or so of flight time.

The sea ice at this time of year is very interesting. Almost the entire Arctic Ocean is frozen over, creating vast ice sheets. Ocean currents and wind push these sheets against each other and they break and crumple into jumbled ridges where they meet. This leaves a totally flat landscape punctuated by randomly-strewn ice chunks, some bigger than houses. It is an otherworldly place to fly over, and to walk through.

This is me crouched in front of some ice blocks near our last capture site, on the sea ice about 30 miles north of the coast of Alaska.

We have been down for weather for several days. After working in Kaktovik last weekend, we used a charter plane to haul all of the USGS gear to Deadhorse. We set up all of their base equipment and got out for a capture on Monday afternoon. It was about 0 degrees (Fahrenheit) and mostly sunny. The weather began to turn that night, steadily becoming warmer, windier, and cloudier. Several inches of snow fell yesterday afternoon as well. All of these factors have reduced visibility to the point where we cannot fly. However, the skies are clearing this afternoon, so we hope to get back out today.

Polar bear tracks in the snow along the Arctic coast in northern Alaska, in October 2008.

Dr. Henry Harlow, Dr. Merav Ben-David, and John Whiteman (left to right) with an adult male polar bear who has been sedated for measurements. They’re sitting in front of a temporary windbreak (to make measurements easier) on sea ice off the northern coast of Alaska in October 2008.

Summer is a critical time for polar bears and climate change is lengthening Arctic summers, which could have a substantial effect on bear populations. However, much of what is known about polar bears comes from studying them out on Arctic sea ice during late winter and spring. During summer, most sea ice retreats far to the north, leaving some bears on shore for several months. Scientists suspect that these bears face difficult conditions on land; temperatures are warm and there’s little to eat. In contrast, some bears follow the retreating ice north, where temperatures are cooler and there may be opportunities to hunt seals.

To find out how polar bears fare in the summer, PhD candidate John Whiteman and his advisors Drs. Henry Harlow and Merav Ben-David are collaborating with scientists from the US Geological Survey and the US Fish and Wildlife Service. They are capturing and examining bears in early summer and attaching GPS-tracking collars, then re-capturing the same bears in late summer and examining them again. Comparing early- and late-summer indicators of body fat, muscle, and diet tells the scientists how well polar bears are faring in summer months. Additionally, they can use this information to forecast how longer Arctic summers may affect polar bear populations.