MIGRATION TRACKING

angel_fang423 Mon Mar 17, 2008 9:25 am

BIRD MIGRATION
Every year, many birds are flying across to another place. The regular seasonal journeys undertake by many birds. It include about the movement of varied distances made in response to changes in food availability , through habitat or weather. Especially, when the weather change to winter . But it usually irregular or in one direction and are termed variously as nomadism. Invasions or irruptions. Birds which does not make seasonal migrations referred to as migratory birds.

THE GENERAL PATTERNS
You would be wondering where the birds travel to and where it stops.
They usually migrate long distances. The common pattern involves flying towards north to breed in the temperate or Arctic summer and returning to wintering gounds in warmer regions to the south.
The advantage of migration is energetic . The more days of northern summer provide, greater opportunities for breeding birds to feed their young. The extended daylight hours allow diurnal birds to produce larger clutches than related non-migratory species that remain in the tropics year-round. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season.

LONG-DISTANCE MIGRATION
The typical image of migration is of northern landbirds such as swallows and birds of prey making long flights to the tropics. Many northern-breeding ducks, geese and swans are also long-distance migrants, but need only to move from their Arctic breeding grounds far enough south to escape frozen waters. Most Holarctic wildfowl species remain in the Northern hemisphere, but in countries with milder climates. For example, the Pink-footed Goose migrates from Iceland to Britain and neighbouring countries. Migratory routes and wintering grounds are traditional and learned by young during their first migration with their parents. Some ducks, such as the Garganey, move completely or partially into the tropics.
SHORT-DISTANCE MIGRATION
Many of the long-distance migrants in the previous section are effectively genetically programmed to respond to changing lengths of days. However, many species move shorter distances, but may do so only in response to harsh weather conditions.
Short-distance passerine migrants have two evolutionary origins. Those which have long-distance migrants in the same family, such as the Chiffchaff, are species of southern hemisphere origins which have progressively shortened their return migration so that they stay in the northern hemisphere.
Those species which have no long-distance migratory relatives, such as the waxwings, are effectively moving in response to winter weather, rather than enhanced breeding opportunities.
In the tropics there is little variation in the length of day throughout the year, and it is always warm enough for an adequate food supply. Apart from the seasonal movements of northern hemisphere wintering species, most species are in the broadest sense resident. However many species undergo movements of varying distances depending on the rainfall.
Many tropical regions have wet and dry seasons, the monsoons of India being perhaps the best known example. An example of a bird whose distribution is rain associated is the Woodland Kingfisher of west Africa.
IRRUPTIONS AND DISPERSAL

Sometimes circumstances such as a good breeding season followed by a food source failure the following year lead to irruptions, in which large numbers of a species move far beyond the normal range. Bohemian Waxwing and Common Crossbills are two species which show this unpredictable variation in annual numbers.
The temperate zones of the southern continents have extensive arid areas, particularly in Australia and western southern Africa, and weather-driven movements are common but not always predictable. A couple of weeks of heavy rain in one part or another of the usually dry centre of Australia, for example, causes dramatic plant and invertebrate growth, attracting birds from all directions. This can happen at any time of year, and, in any given area, may not happen again for a decade or more, depending on the frequency of El Niño and La Niña periods.

Bird migration is primarily, but not entirely, a Northern Hemisphere phenomenon. In the Southern Hemisphere, seasonal migration tends to be much less obvious. There are several reasons for this.
First, the largely uninterrupted expanses of land mass or ocean tend not to funnel migrations into narrow and obvious pathways, making them less obvious to the human observer. Second, at least for terrestrial birds, climatic regions tend to fade into one another over a long distance rather than be entirely separate: this means that rather than make long trips over unsuitable habitat to reach particular destinations, migrant species can usually travel at a relaxed pace, feeding as they go. Short of banding studies it is often not obvious that the birds seen in any particular locality as the seasons change are in fact different members of the same species passing through, gradually working their way north or south.
PHYSIOLOGY AND CONTROL

The control of migration, its timing and response are genetically controlled and appear to be a primitive trait that is present even in non-migratory species of birds. The ability to navigate and orient themselves during migration is a much more complex phenomenon which may include both endogenous programs as well as learning.