Tuesday, October 20, 2009

Winter Weather

Man, we've encountered a stretch of bad weather that just won't quit. Since my last post, we've flown a total of two days! Mostly it's been thick fog keeping us on the ground, but today it's a flat out blizzard. Granted, we captured bears on both days, but it's been slim pickings for awhile now. Luckily we're down to the last bear that we need to capture. Only problem is that she's currently 8 miles out swimming in the ocean. So unless she decides to swim back towards land, our capture season may soon be drawing to a close.

This may be a good time to elaborate a little bit about the ecology of polar bears up here. I think I've already mentioned that most of the polar bears from the Beaufort Sea population (that's the one we're working with) follow the retreating sea ice to the north every summer. However, a small portion of the bears choose to stay on shore during the summer. The drawback to staying on shore is that polar bears are typically very poor hunters on land. The bears are quite reliant on the sea ice as a platform from which they can hunt seals. At this time of year, the sea ice is just starting to form on the coastlines, called "land fast" ice. At the same time, the polar ice pack is starting to creep down from the north and will eventually connect with the land fast ice. So the polar bears that we've been capturing on land are starting to think about returning to the ice. In fact, I've seen several seals hauled out on ice already. Get set for lunch, right?

Well, not for all bears. The pregnant females will stay on land and hunker down in a den for the winter, giving birth to their cubs sometime in January / February. Unlike brown bears and black bears that hibernate in a den all winter de facto, the only polar bears that bed down for winter are these pregnant females. The rest of the population will stay out on or near the sea ice. We've already started to see bears digging prospective den sites, usually in pretty heinous snow banks. Today's blizzard aside, den sites have been pretty hard to come by due to the warm weather we've had lately. We even saw one female trying to den in the Brooks Range, 30 or 40 miles from the coast where there is more snow in the mountains (polar bears are usually found right next to the ocean).

Armed with your new found information on polar bears, do you think our last bear is pregnant? That is the million dollar question for our group right now.

I've seen all kinds of different ice up here. This is a photo of ice just starting to form up next to the shore, "shore fast" ice. The ocean has a slightly lower freezing point (29F) compared to fresh water (32F). This is due to the much higher salt content of ocean water, the same reason you put salt on an icy road.

Often the ice is composed of a multitude of appropriately named pancakes. Pancake ice is formed when the top layer freezes, but wave action breaks it up into these pieces. After bouncing off each other for awhile, the edges of the pancakes get turned up and rounded.

Occasionally you encounter really smooth ice, perfect for sliding on (Dana Petersen photo).

Here are a couple of the seals we saw the other day. They keep breathing holes open in the ice, and seconds after we flew over, they dove down the holes. Polar bears often hunt the seals by ambushing them when they pop out of their breathing holes (Dana Petersen photo).

We've certainly been seeing quite a few polar bears when the weather permits flying. These polar bears were out on a barrier island that was surrounded by fresh ice.

Any idea what this is? It's a potential denning site for a pregnant female. They excavate all over the place, usually in big snowdrifts like this, looking for the perfect spot to pop out a few puff balls (Dana Petersen photo).

It almost looks like this polar bear smiled for the picture. I like to think she was just really stoked about contributing to science.

Despite my best efforts to keep my birthday under wraps, somehow word leaked out. I'm glad it did, the cake was quite tasty. My favorite part was that they put an emergency strobe light on it for a candle. Thanks polar bear crew!