A young fox on these barren wastes may have to travel 100 km a day, serching for food. Scratching for scraps and scavenging from others; it's a meager existence. And the worst of the winter is still to come. By midwinter, temperatures drop to minus 50 degrees Celsius, and deep snow makes scavenging nearly impossible. But a faint sound beneath the snow may be this fox's salvation; Lemmings. It's time to become a hunter. But catching what you can't see is not easy. It's hard to judge the leap, and the depth of the snow. Too deep, and you get stuck. Too shallow, and it can be rather painful. It's going to take time, but mastering lemming hunting is vital if a young fox is to make it through the winter. At last, this fox is on his way. But if he is to survive until spring, he'll need to make a catch like this every couple of days.
Hungry Polar Bear Ambushes Seal - The Hunt - BBC Earth
At this time of year, pollar baers, on average, succeed only once in twenty hunts. If the hunter is skinny like this one, that may not be often enough. All she can do is keep trying. To prevent her scent betraying her, she makes a wide sweep to get downwind of the seal. Getting close. She is now right behind the seal. Incredibly, she caught the seal under water. It's only small, but even so, its blubber alone will contain a hundred thousand calories; enough to sustain this bear for a week. And in that time, she might even catch another. But this can't go on forever. As summer continue, templatures are rising. Each hunt requirs more energy, draining the bears more reserves.
Tips that may not be often enough: "that"は"once in twenty hunts"。「この割合は十分な頻度ではない」
a hundred thousand calories: 英語ではグラムカロリーとキロカロリーを区別しない。表記では"cal"と"Cal"になる。日本語ならここは10万キロカロリーとするところ。
draining: 接続詞+主語+動詞を「コンマ+ing」で表す。ドキュメンタリーでは頻出。"Each hunt requirs more energy, and the hunt drains the bears more reserves".