Monday 6 June 2011

Life in the Fridge*

A harbor seal on ice, South Sawyer Glacier, Alaska  

They say firewood warms you three times: collecting it, splitting it and burning it. During the latest blast of wintery weather, while my thrice-warmed body relaxed by the fire, my curious mind was free to wander in comfort. It got to thinking about how other mammals deal with the cold.

A few years back we had the privilege of spending time in Alaska. Before you get mental images of snow and ice and polar bears, I should quickly add that we were there in summer, and in the relatively mild south-east. Except for the highest parts, the area is dominated by coniferous forest and intricate and rich waterways.

But it can still get cold, and the incredibly diverse wildlife of both sea and land has had to adapt to that. We were fortunate enough to see some of the amazing variety of mammals that live in and around Alaska’s Inside Passage.

Largest of all were the whales, mainly humpback, but also grays. The area is a hot-spot for humpbacks, providing both large amounts of food (krill) and vast sheltered waterways. Their protection against the cold water is two-pronged: fuel and insulation. Digesting food gives the body energy, and thus warmth. But the right kind and quantity of food also builds up a fatty layer (blubber) just beneath the skin. It can be up to 15cm thick, and keeps the whale’s body warm even in freezing cold water.

A mother humpback whale and calf in the Inside Passage, Alaska 

Steller sea lions and harbor seals use a similar tactic, building up layers of blubber that can account for up to 30% of their weight during winter. Both have extremely fat-rich milk, enabling their pups to quickly put on weight, including the all-important insulating layer of blubber. Although both of these pinnipeds have some hair, the hair has absolutely no insulating value.

Steller sea lions hauled out on a rock in Sitka Sound, Alaska 
That contrasts starkly with the defence against cold used by sea otters. We came across a raft of these charming aquatic mammals in Sitka Sound. They were swimming and resting in the kelp-covered shallows, occasionally surfacing with shell-fish, which they ate using their tummies as a table. We approached slowly, engine off, so as not to scare the skittish mammals. They’ve been hunted close to extinction, so their wariness is justified.

Sea otters dining in the shallows, Sitka Sound, Alaska 
Apart from fuelling themselves via a rich shell-fish diet, sea otters have the densest fur of any mammal. Hair density can reach an amazing 165,000 hairs per square cm, equating to hundreds of millions of hair fibres per otter. Only God is supposed to know how many hairs humans have on their head (see Luke 12:7), but scientists estimate a mere 150 000 in total. And that's if we've kept them all! 

Only one other mammal comes close to this hirsute sea otter, and that’s Australia’s unique monotreme, the platypus. Body fat becomes far less important to these creatures, as their dense fur traps air and excludes water, both of which keep the body warmer. 

On land we came across a mammal which uses yet another tactic to cope with life in the fridge. Bears, both Alaskan brown (or grizzly), and the black variety, live in south-east Alaska. We got uncomfortably close to the obligatory three bears, although in our case it was a momma bear and two baby bears (papa bear, thankfully, didn't show). Although the state of their fur and the amount of fat they carry are still important, bears also beat off the cold by hibernating through the winter months.

Interestingly, Australia's other monotreme, the echidna, also hibernates. In fact echidnas lower their temperature far further, and hibernate more deeply, than do bears.

Meanwhile there's snow on Kunanyi/Mt Wellington, and I’m carefully considering my cold-beating options. I'm not keen to add blubber, and my hair density only looks like heading south. While hibernation also has its attractions, I think I’ll settle for food (in moderation) and fire to protect me from the cold. That and the feathers that fill my doona and down jacket. I bless the geese that kindly loaned me those!

When Alaska was purchased from the Russians in 1867 for $7.2million (about 2c an acre), it was derided by the press and many politicians as a waste of money for a useless “ice-box”.

1 comment:

lucychili said...

interesting observations
and comparisons =)