Lower invertebrates Many marine invertebrates travel considerable distances during certain seasons. A large proportion of them, however—particularly planktonic organisms, plant and animal aquatic drifters—do not travel deliberately but are carried by ocean currents.
Historical views[ edit ] Records of bird migration were made as much as 3, years ago by the Ancient Greek writers HesiodHomerHerodotus and Aristotle. Pliny the Elderin his Historia Naturalisrepeats Aristotle's observations. This belief persisted as late aswhen Elliott Coues listed the titles of no less than papers dealing with the hibernation of swallows.
Even the "highly observant"  Gilbert Whitein his posthumously published The Natural History of Selbornequoted a man's story about swallows being found in a chalk cliff collapse "while he was a schoolboy at Brighthelmstone", though the man denied being an eyewitness.
The Rostocker Pfeilstorchfound indemonstrated that birds migrated rather than hibernating or changing form in winter. Swallows frequently roost at night, after they begin to congregate, by the sides of rivers and pools, from which circumstance it has been erroneously supposed that they retire into the water.
These experiments have since been amply confirmed by Nattererof Vienna Flocks of birds assembling before migration southwards probably common starling Migrating waders in Roebuck BayWestern Australia Migration is the regular seasonal movement, often north and south, undertaken by many species of birds.
Bird movements include those made in response to changes in food availability, habitat, or weather. Sometimes, journeys are not termed "true migration" because they are irregular nomadism, invasions, irruptions or in only one direction dispersal, movement of young away from natal area.
Migration is marked by its annual seasonality. Approximately of the world's 10, bird species are long-distance migrants.
The most common pattern involves flying north in the spring to breed in the temperate or Arctic summer and returning in the autumn to wintering grounds in warmer regions to the south.
Of course, in the southern hemisphere the directions are reversed, but there is less land area in the far south to support long-distance migration.
This helps diurnal birds to produce larger clutches than related non-migratory species that remain in the tropics. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season.
Predation can be heightened during migration: Eleonora's falcon Falco eleonorae, which breeds on Mediterranean islands, has a very late breeding season, coordinated with the autumn passage of southbound passerine migrants, which it feeds to its young.
A similar strategy is adopted by the greater noctule batwhich preys on nocturnal passerine migrants. The migrating birds bypass the latitudes where other populations may be sedentary, where suitable wintering habitats may already be occupied.
This is an example of leap-frog migration. Female chaffinches Fringilla coelebs in Eastern Fennoscandia migrate earlier in the autumn than males do  and the European tits of genera Parus and Cyanistes only migrate their first year.
Often, this front narrows into one or more preferred routes termed flyways.
These routes typically follow mountain ranges or coastlines, sometimes rivers, and may take advantage of updrafts and other wind patterns or avoid geographical barriers such as large stretches of open water.
The specific routes may be genetically programmed or learned to varying degrees. The routes taken on forward and return migration are often different. Many, if not most, birds migrate in flocks.The late Sudanese author Tayeb Salih's Season of Migration to the North is an engaging and complicated novel, by turns combative and wistful, about two men who leave Sudan to .
After many years of study in Europe, the young narrator of Season of Migration to the North returns to his village along the Nile in the Sudan, eager to make a contribution to the new postcolonial life of his country.
Back home, he discovers a stranger among the familiar faces of . Season of Migration to the North is a rich and sensual work of deep honesty and incandescent lyricism.
In it was selected by a panel of Arab writers and critics as the most important Arab novel of the twentieth century.5/5(2). After years of study in Europe, the young narrator of Season of Migration to the North returns to his village along the Nile in the Sudan.
It is the s, and he is eager to make a contribution to the new postcolonial life of his country/5(K). "Season of Migration to the North is an engaging and complicated novel, by turns combative and wistful, about two men who leave Sudan to study in England and afterward belong in neither place." --Maude Newton, grupobittia.com /5(56).
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