Therefore the tree line has now been accepted as the southern boundary of the Arctic.
The tree line is not, however, a clear-cut boundary which sharply separates dense stands of forest from completely treeless barren grounds.
When this limit is passed the trees generally grow shorter, but the forest continues as islands or scattered trees, sometimes following watercourses far into the otherwise treeless country.
As a result of wind and snow blast, the trees farther north eventually become dwarfed and stunted, and finally disappear completely. Near the limit of existence trees can grow only under especially favorable conditions, and are therefore restricted to valleys of rivers, south-facing and well-drained slopes, sheltered depressions or calcareous soil.
Transitional zone between the timber line and the actual tree limit may attain a breadth of more than sixty miles and has received various names. In Russia, for example, it is colled lesotundra(forest-tundra) while in Canada it is known as the Hudsonian Zone. A widely used and very appropriate name is the subarctic zone.
линька molt, moult, molting
About a month or more after leaving the nest, fledglings begin to exchange the contour feathers of the head, back and belly for the so-called first-winter plumage. Occasionally, wing- and tail-feathers are partly replaced as well. As a result, the small feathers are the new ones in the first-winter plumage, while the bulk of wing- and tail-feathers are retained from the juvenile plumage.
изгнездовогонарядавпервыйзимний post-juvenile molt (from juvenile plumage into first-winter one)
Six heathland sites were used in the present study. These included samples of all types of habitats occupied by wheatears (каменки, Aves), ranging from bare sand, through extremely short-cropped turf, to longer grass, sand sedge (Carex sp.) and heather (Calluna vulgaris).
There is a marked preference for nesting in abandoned caves, if available, and the highest breeding density are reached in areas with abundant caves. These caves offer constant moderate temperatures in aqenvironment characterized by thermal extremes.
The boulder-fields are the preferred habitat of this bird species, which occurs only rarely above the Cave Sandstone belt.
Birds are found from near sea-level to 1 500 m elevation, locally to 2 200 m. They are quite flexible in their habitat requirements.
Therefore, these birds avoid barren areas and, conversely, are locally quite common in cultivated valleys of the Elburz Range.
segregation of closely related`species
гетерогенности ~ степень extent of habitat heterogeneity
качество ~ habitat quality
конкуренциямежвидоваяиз-за ~ interspecific competition for habitat
обеспечивать provide (for; with); secure (такжегарантировать)
Construction of the jaw apparatus is adapted to several different functions. On the one hand, it provides an opportunity for fine manipulations of very small objects; on the other, it permits the development of violent forces necessary for tearing up large prey.
Further study is required to investigate whether social ranking and contest competition in ungulate herds can secure preferred central positions as it does in some primate groups.
Many reindeer breeders stay permanently in the forests, while others are nomads who in summer visit the arctic tundras with their herds and, in addition, hunt and fish along the coasts of the Arctic Ocean.
The ability to detect the presence of another animals territory when tunneling may inhibit a neighbouring mole-rat from unwanted and unexpected invasion of an adjacent tunnel system as well as postpone an aggressive encounter.
Male philopatry is associated with generally low tolerance between male group mates, although males cooperate against extra-group males. However, data given here show that within-group male alliances can occur in groups with more than two males.
As stated previously, however, deep snow confined lions to the drainage, usually below 5,500-6,000 ft, and restricts movement other than down-drainage.
Life in the High Arctic made extensive traveling necessary, and by means of dog sledges the Eskimos were capable of covering great distances within a short time. This extensive nomadism facilitated the exchange of experience and the diffusion of cultural elements through the whole community.
The continuous traveling tended to maintain a specific cultural resemblance across vast areas.
переносить (претерпевать, напр., стресс) v endure, undergo