TEXT 1

Nature’s cradle

Female polar bears dig large dens in the snow where they will spend the winter and give birth. Cubs are born in December or January and are blind, hairless, and no bigger than a squirrel (01). The cubs (02) grow rapidly from the rich milk provided by their mother. The cubs remain with their mother for about 2 1/2 years. Male and female Dall sheep live in separate bands except during mating (06) season in November and early December. Afterward the females return to their band and the lambs (03) are born in May. The lambs are cared for by their mothers.

On average, five gray wolf pups are born in early spring to the pair. The pups (04) are reared (07) in the den for the first six weeks and are dependent on their mother’s milk the first month. They are gradually weaned (08) and then fed by the pack. By eight months they are almost fully grown and begin traveling with the adults.

The mother duck lays an egg or two every day until she has a full nest - usually 8 to 15 - at which point she’ll sit on the eggs. It then takes 28 days for the eggs to hatch. Once hatched (09), the mother leads her ducklings (05) to the nearest source of water.

(Source: 2008 Wildlife Land Trust Calendar)

According to the text, polar bears develop fast after they are born because they