Context and question: Within a species not all populations may be migratory; this is known as "partial migration". Partial migration is very common in the southern continents; in Australia, 44% of non-passerine birds and 32% of passerine species are partially migratory. In some species, the population at higher latitudes tends to be migratory and will often winter at lower latitude. 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. Many fully migratory species show leap-frog migration (birds that nest at higher latitudes spend the winter at lower latitudes), and many show the alternative, chain migration, where populations 'slide' more evenly north and south without reversing order.
What is partial migration?
Answer: not all populations may be migratory
Context and question: Most birds can fly, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for breeding, feeding, and predator avoidance and escape. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil. Wing shape and size generally determine a bird species' type of flight; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are flightless, as were many extinct birds. Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators. Though flightless, penguins use similar musculature and movements to "fly" through the water, as do auks, shearwaters and dippers.
What distinguishes birds from almost all other vertebrate classes?
Answer: Most birds can fly,
Context and question: The region was dominated by Bantu-speaking tribes, who built trade links leading into the Congo River basin. Congo-Brazzaville was formerly part of the French colony of Equatorial Africa. Upon independence in 1960, the former colony of French Congo became the Republic of the Congo. The People's Republic of the Congo was a Marxist–Leninist one-party state from 1970 to 1991. Multi-party elections have been held since 1992, although a democratically elected government was ousted in the 1997 Republic of the Congo Civil War and President Denis Sassou Nguesso has ruled for 26 of the past 36 years.
What year was President Denis Sassou Nguesso ousted? 
Answer:
unanswerable