Gannets are large, striking seabirds known for their impressive diving capabilities. These marine birds spend much of their lives over the open ocean, coming to land primarily for breeding. Their existence is deeply intertwined with the sea, from specialized hunting techniques to social nesting habits.
Distinctive Characteristics
Gannets are substantial birds, measuring 87 to 100 centimeters in length with a wingspan of 170 to 180 centimeters. They weigh between 2.3 and 3.6 kilograms. Adult gannets exhibit predominantly white plumage, accented by dark brown or black wingtips. Their head and neck often display a yellowish wash, which becomes more pronounced during the breeding season.
Their eyes are pale blue or white, encircled by a dark ring or a pale blue eye-ring with a black line. These birds possess excellent vision, specially adapted for seeing underwater immediately after striking the surface. They have a long, conical, pointed bill, blue-grey with bare black skin around the mouth and eyes. Gannets also have unique physical adaptations for their diving lifestyle, including the absence of external nostrils, located inside the mouth. Additionally, subcutaneous air sacs in their face and chest function like natural airbags to cushion the impact when they hit the water.
Oceanic Lifestyle
Gannets primarily inhabit the open ocean, preferring areas where their main prey species are abundant. They subsist almost entirely on fish, consuming species that shoal near the surface, typically ranging from 2.5 to 30.5 centimeters in length. Their diet includes mackerel, herring, sandeels, sardines, anchovies, cod, smelt, and occasionally squid.
These birds are known for their spectacular plunge-diving hunting technique. They locate prey from altitudes up to 70 meters above the water. Once spotted, they fold their wings back and dive headfirst into the water, reaching speeds of up to 100 kilometers per hour. This high-speed entry allows them to penetrate the water up to 11 meters deep, and they can swim deeper, using both wings and feet for propulsion underwater. They seize fish during descent or ascent, often swallowing smaller prey while submerged.
Gannets are powerful flyers, alternating between flapping and gliding as they cover vast distances. Their long, narrow wings efficiently utilize air currents, allowing them to travel extensively, up to 320 kilometers from nesting sites in search of food. When cruising, they maintain speeds between 48 and 64 kilometers per hour.
Nesting Colonies
Gannets are highly colonial birds, establishing large breeding grounds known as gannetries, often on towering cliffs, isolated islands, or coastal stacks. Gannets form lifelong pair bonds and return to the same nesting site each year to breed.
Courtship rituals involve intricate displays, including bowing, head-shaking, bill-fencing, and mutual preening, which strengthen the pair bond. Males primarily build nests, constructing a compressed pedestal from materials such as grass, algae, feathers, mud, and guano.
A single, smooth, pale blue egg is laid. Both parents share incubation duties for 40 to 45 days, using the warmth from their webbed feet as gannets lack a brood patch.
Chicks are altricial, meaning they are born nearly naked before developing thick white down. Both adults feed the young by regurgitating partially digested fish. Chicks fledge around three months after hatching. Gannet colonies are notably noisy with raucous calls, and emit a strong, distinct odor.