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The huge male polar bear patrols nearby.
一頭龐大的公熊在附近徘徊。
The bear knows that whales must come up for air every twenty minutes.
它知道白鯨每隔二十分鐘必定會探出水面進行呼吸。
The polar bear is the largest land predator on the planet and males can weigh up to eight hundred kilos.
北極熊是地球上體型最大的陸地掠食者，而公熊的體重可以達到八百公斤。
Each beluga weighs almost twice that.
每頭白鯨的體重幾乎是它的兩倍。
If he can succeed in catching one, a beluga would provide this bear with the substantial meal.
如果它能夠成功地捕捉到一頭，那么就會是一頓豐盛的美餐。
But a four-meter long whale is a challenging prey to catch.
不過體長四米的白鯨卻并非是唾手可得的獵物。
The bear rolls in the snow to remove salt crystals from its fur.
北極熊在雪地上打著滾以去除粘在它毛皮上的鹽晶。
Salt makes the fur less effective insulated.
鹽會使毛皮的隔熱保暖功能下降。
These belugas have been attacked by many bears over the last six months. Some have been caught.
這些白鯨在最近的六個月里曾經遭到許多北極熊的襲擊。有些甚至被捉到。
Belugas have a layer of blubber up to fifteen centimeters thick.
白鯨身上有一層厚達到十五厘米的鯨脂。
For the bear, this catch brings a meal rich in energy.
對北極熊來說這樣的美餐能帶來充足能量。
At this time of the year, gulls depend on scavenging from polar bear kills to survive.
每年的這個時候海鷗們都依靠撿食北極熊捕食后的殘羹剩飯而生存。
Soon, the ice covering the Arctic Ocean begin to melt.
很快覆蓋北冰洋的冰層開始融化了。
Only then will the belugas have a chance to escape to open water.
直到這時白鯨們才有機會逃往開闊水域。
It's mid March in the Arctic, and the days are growing longer.
時值三月中旬，北冰洋白晝逐漸變得更長。
In Svalbard, the mother bear and her cubs are emerging from their winter den.
在斯瓦爾巴德群島，母熊和孩子們從過冬的洞中探出身來。
The cubs are now three-month old and they weigh over ten times as much as they did when they were born.
小熊們現在三個月大了，而體重也已經超過了剛出生時的十倍。
Rolling in the snow helps clean her fur, but the whole family seems to be enjoying the fresh air and sunshine.
在雪地上打滾有助于清潔毛皮，而這一家子似乎很享受新鮮的空氣與燦爛的陽光。
The bears will stay near the den for the next two weeks, returning to its warmth if the weather closes in.
它們還會在洞穴附近再呆上兩周以便在風暴來臨時回到溫暖的洞中。
Adult polar bears have perfectly adapted to life in this extreme environment.
成年北極熊已經完美地適應了這種極端環境下的生活。
Underneath the dense white fur, the mother bear skin is black to help absorb the meager heat of the Arctic sun.
母熊濃密的白色毛皮下面是黑色的皮膚，這有助于吸收北極非常稀少的太陽熱量。
And beneath the skin, lies a layer of fat more than ten centimeters thick which helps maintain body heat.
而在皮膚下面則是一層厚度超過十厘米的脂肪，有助于維持體內熱量。
But at this young age, the cubs have very little fat to insulate them.
不過小熊們年齡還太小體內脂肪也很少，不足以保持熱量。
They rely on the energy of their mother's milk to keep them warm. But she hasn't eaten for months.
它們要依靠母乳供給的能量來保暖。但母熊已經數月沒吃東西了。
Surviving only on her fat reserves, she has lost a third of her body weight.
它僅僅依靠體內貯存的脂肪生存，因此體重已經下降了三分之一。
Very soon, she must head for the rich hunting grounds of the sea ice.
不久后，它就必須前往海冰上富饒的獵場捕食了。
