are similar. According to Nelson northern gannets can recognize the call of their breeding partner, their chicks and birds in neighbouring nests. Individuals from outside this sphere are treated with more aggression. Distribution and habitat The northern gannet's breeding range is on both sides of the North Atlantic on coasts influenced by the Gulf Stream, There are colonies in the Gulf of Saint Lawrence and on the islands off the east coast of Canada. They normally nest in large colonies, on cliffs overlooking the ocean or on small rocky islands. The water needs to be cool enough for Atlantic mackerel and herring, which are the main food source for the northern gannet. These areas also overlie the continental shelf. Northern gannet colonies can be found in the far north in regions that are very cold and stormy, and Nelson has suggested that they can survive in these regions for several reasons, including the combination of body weight and a powerful beak that allows them to capture strong muscular fish, and the ability to dive to great depths and capture prey far from the cliffs. Their fat reserves act as weight when diving and as reserves during extended periods without food. The northern limit of their breeding area depends on the presence of waters that are free of sea ice during the breeding season. Therefore, while Greenland and Svalbard offer suitable breeding sites, the Arctic regions have summers that are too short to allow the northern gannets to lay their eggs and raise a brood, which requires between 26 and 30 weeks. The southern limit of their distribution mainly depends on the presence of sufficient prey. There is fossil evidence of northern gannets breeding on Crete in the Pleistocene. Breeding colonies Some northern gannet breeding colonies have been recorded as being located in the same place for hundreds of years. The cliffs containing the colonies appear white when seen from a distance, due to the number of nesting birds present on them. There is a written record of a colony on the island of Lundy from 1274. There were only 70 nests by 1871, and the colony finally disappeared by 1909 at the latest. More than two-thirds of the world population breeds around the coasts of the British Isles. Colonies include: Scotland Bass Rock, off the Firth of Forth, first recorded in 1493. In 2004, it contained more than 48,000 nests.