Many bird species migrate to take advantage of global differences of seasonal temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds, shorebirds, and waterbirds undertake annual long distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the temperate or polar regions and a non-breeding season in the tropical regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs. Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around 2,500 km (1,600 mi) and shorebirds can fly up to 4,000 km (2,500 mi), although the bar-tailed godwit is capable of non-stop flights of up to 10,200 km (6,300 mi). Seabirds also undertake long migrations, the longest annual migration being those of sooty shearwaters, which nest in New Zealand and Chile and spend the northern summer feeding in the North Pacific off Japan, Alaska and California, an annual round trip of 64,000 km (39,800 mi). Other seabirds disperse after breeding, travelling widely but having no set migration route. Albatrosses nesting in the Southern Ocean often undertake circumpolar trips between breeding seasons.
When do birds substantially increase body fats and reduce the size of some of their organs?
Before migration

By 1957, pan-Arabism was the dominant ideology of the Arab world, and the average Arab citizen considered Nasser his undisputed leader. Historian Adeed Dawisha credited Nasser's status to his "charisma, bolstered by his perceived victory in the Suez Crisis". The Cairo-based Voice of the Arabs radio station spread Nasser's ideas of united Arab action throughout the Arabic-speaking world and historian Eugene Rogan wrote, "Nasser conquered the Arab world by radio." Lebanese sympathizers of Nasser and the Egyptian embassy in Beirutthe press center of the Arab worldbought out Lebanese media outlets to further disseminate Nasser's ideals. Nasser also enjoyed the support of Arab nationalist organizations, both civilian and paramilitary, throughout the region. His followers were numerous and well-funded, but lacked any permanent structure and organization. They called themselves "Nasserites", despite Nasser's objection to the label (he preferred the term "Arab nationalists").
Who said that Nasser conquered the Arab workd with radio?
Eugene Rogan

As the number and size of agricultural societies increased, they expanded into lands traditionally used by hunter-gatherers. This process of agriculture-driven expansion led to the development of the first forms of government in agricultural centers, such as the Fertile Crescent, Ancient India, Ancient China, Olmec, Sub-Saharan Africa and Norte Chico.
What type of expansion was it in places like the Fertile Crescent?
agriculture-driven