Migratory birds may use two electromagnetic tools to find their destinations: one that is entirely innate and another that relies on experience. A young bird on its first migration flies in the correct direction according to the Earth's magnetic field, but does not know how far the journey will be. It does this through a radical pair mechanism whereby chemical reactions in special photo pigments sensitive to long wavelengths are affected by the field. Although this only works during daylight hours, it does not use the position of the sun in any way. At this stage the bird is in the position of a boy scout with a compass but no map, until it grows accustomed to the journey and can put its other capabilities to use. With experience it learns various landmarks and this "mapping" is done by magnetites in the trigeminal system, which tell the bird how strong the field is. Because birds migrate between northern and southern regions, the magnetic field strengths at different latitudes let it interpret the radical pair mechanism more accurately and let it know when it has reached its destination. There is a neural connection between the eye and "Cluster N", the part of the forebrain that is active during migrational orientation, suggesting that birds may actually be able to see the magnetic field of the earth.
How does the magnetic field help the bird at different latitudes?
let it know when it has reached its destination

Grande Saline Bay provides temporary anchorage for small vessels while Colombier Bay, to the northwest, has a 4 fathoms patch near mid entrance. In the bight of St. Jean Bay there is a narrow cut through the reef. The north and east sides of the island are fringed, to a short distance from the shore, by a visible coral reef. Reefs are mostly in shallow waters and are clearly visible. The coastal areas abound with beaches and many of these have offshore reefs, some of which are part of a marine reserve.
Reefs are almost always in what type of water?
shallow

According to the Primary Chronicle, the territories of the East Slavs in the 9th century were divided between the Varangians and the Khazars. The Varangians are first mentioned imposing tribute from Slavic and Finnic tribes in 859. In 862, the Finnic and Slavic tribes in the area of Novgorod rebelled against the Varangians, driving them "back beyond the sea and, refusing them further tribute, set out to govern themselves." The tribes had no laws, however, and soon began to make war with one another, prompting them to invite the Varangians back to rule them and bring peace to the region:
In what year did the Slavic and Finnic tribes rebel againts the Varangians?
862