Ravens were used by Vikings to determine if there was a land ahead during their long voyages across the open sea. They carried ravens with them in cages. When they found themselves far away from the shore and didn’t know which way to go, they would set a raven free.
Raven would fly high in the air and then start flying in circles searching for land in the distance. Because ravens can’t land on water, if the raven could not see a land, he would return to the ship. But if the raven saw land in the distance, it would fly straight for it. All the Vikings had to do is follow the raven.