Northern Gannets are the largest North Atlantic seabird, with a 2 metre wingspan. They winter off the coasts of Western Europe, as far south as West Africa, returning to the Alderney colonies of Les Etacs and Ortac from late January. They are powerful fliers, using the lift generated by rising air over ocean swells close to the surface of the sea, to fly effortlessly over long distances to forage (typically up to 200km over 24 hours). They are superbly streamlined and adapted for both flight and swimming underwater. Their sharply pointed beaks and heads contain special fluid filled sacs, as adaptations to absorb the shocks of striking the water at up to 100mph, and their very long wings, as well as being superbly efficient in soaring and gliding flight, can be pulled back into a dart shape to enable the gannet to enter the water with barely a splash.
Gannets feed on fish taken by plunge diving from heights of 10-40m, and can dive to similar depths underwater. They will also swim on the surface with heads immersed, and then dive for available fish. They usually forage in large flocks over shoals of prey species, but will also feed singly. Female gannets seem to be more selective than males in the areas where they forage, and also make longer, deeper dives. They spend more time on the sea surface than males. Fish and offal, especially discards from trawlers, are also taken, and may have been partially responsible for the dramatic increases in the past twenty years at colonies such as Alderney, and Bempton Cliffs in Yorkshire
Satellite-tagged gannets have revealed the destinations of foraging trips. In the English Channel area, three main feeding areas for Alderney’s birds have been identified: in Lyme Bay, off the south coast of Dorset and Devon, and in the Bays of Le Havre, off northern Normandy, and Mont St Michel, south of Jersey. Offshore tidal fronts such as those around Alderney, where there are turbulent currents bringing nutrients, and fish, close to the surface, are also important feeding grounds. The sight of large V-shaped formations of pure white gannets, flying close to the surface on their return to their colonies, is one of the most evocative bird spectacles from Alderney’s cliffs.
Gannet are opportunist hunters, changing their prey species through the season, and they have adapted well to the EU’s wasteful fishery discards regime. In 1940, a single pair bred on Les Etacs, and at the last count in 2011, over 5,750 pairs were counted, with over 2,100 additional pairs on nearby Ortac. Including in non-breeding juvenile birds (up to 4 years old), there may be up to 20,000 gannets in the seas around Alderney at the height of the breeding season, with all birds, bar a very few juveniles, leaving Alderney’s waters entirely between November and January. Our resident birds will regularly visit the traditional commercial fishing grounds for herring, mackerel and sand eel. Northern gannets often feed in association with cetaceans such as dolphins and whales, which herd fish shoals into ‘bait balls’ near the surface. The gannets then plunge dive repeatedly into the bait ball to take their prey easily with rapid, shallow dives.