The term ‘tree-line’ describes the height above which trees can no longer grow in the mountains. The main reason for this is the very low temperature in these places. If we climb a mountain, we find a temperature drop of about 6°C for every kilometre. In addition, the temperature fluctuations between day and night as well as summer and winter are very high. The soil cover is thin so the roots of trees do not get a firm hold. Only small pine trees, cedars, grass, and moss grow above the tree-line before the start of the rocky and icy area.
Groundhogs live in widely branched burrows below the ground, but come out on the surface every day to collect grasses, seeds, and insects. A few species live in colonies in high mountains. They divide work amongst them—when a few animals have gone out in search of food, the others are on guard. If they sense danger from approaching enemies, they emit a shrill whistle to warn the others. In the summer, the animals must feed enough to put on a thick layer of fat so that they can survive the 6-9 months long winter sleep. 
Both animals have adapted to their mountain habitat. The chamois live in the upper mountain forests and fields and climb higher only in summers. The ibexes, on the other hand, live in icy and rocky regions and look for food in mountain meadows. They never go down to the forest. Species of ibexes are found in the mountain regions of Europe and Asia, on the Arabian Peninsula, and in north-eastern Africa. Chamois, on the other hand, are found only in the mountains of Europe: in the Alps, Carpathian Mountains, and Pyrenees as well as in Caucasus Mountains. 
Most of the forest ants build hills at sunny forest edges from needles, twigs, and moss. The well-organized huge colonies of ants are called ‘hills’. Several hundred queens live with their ‘community’ in these hills. The ants divide the work among themselves. While the queens lay eggs, the soldier ants must provide protection for the eggs and the worker ants get food for the larvae. In the month of June, the winged male and female ants hatch. The males die after the nuptial flight. The impregnated young queens look for a new ground or return to the old one to lay eggs.
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