The Razorbill Auk (Alca torda) is a colonial seabird that only comes to land in order to breed. This agile bird chooses one partner for life; females lay one egg per year. Razorbills nest along coastal cliffs in enclosed or slightly exposed crevices. The parents spend equal amounts of time incubating. Once the chick has hatched, the parents take turns foraging for their young and sometimes fly long distances before finding prey.
The razorbill is primarily black with a white underside. The male and female are identical in plumage; however, males are generally larger than females. In 1918, the razorbill was protected in the United States by the Migratory Bird Treaty Act. Presently, the major threat for the population is the destruction of breeding sites.
The razorbill is in the family Alcidae and its genus is Alca. It is closest living relative to the great auk (Pinguinis impennis), which is now extinct. The Alcini clade also includes the common murre (Uria aalge), the thick-billed murre (Uria lomvia) and the dovekie (Alle alle).[8]
Razorbills are distributed across the North Atlantic; the world population of razorbills is estimated to be at less than 1,000,000 breeding pairs, making them among the rarest auks in the world. Approximately half of the breeding pairs occur in Iceland. Razorbills thrive in water surface temperature below 15°C. They are often seen with other larger auks, such as the thick-billed murre and common murre. However, unlike other auks, they commonly move into larger estuaries with lower salinity levels to feed. These birds are distributed across sub-arctic and boreal waters of the Atlantic. Their breeding habitat is islands, rocky shores and cliffs on northern Atlantic coasts, in eastern North America as far south as Maine, and in western Europe from northwestern Russia to northern France. North American birds migrate offshore and south, ranging from the Labrador Sea south to the Grand Banks of Newfoundland to New England. Eurasian birds also winter at sea, with some moving south as far as the western Mediterranean. Approximately 60 to 70% of the entire razorbill population breeds in Iceland.
The life history traits of the razorbill are similar to that of the common murre. However, razorbills are slightly more agile. During breeding, both male and female protect the nest. Females select their mate and will often encourage competition between males before choosing a partner. Once a male is chosen, the pair will stay together for life.
Throughout the pre-laying period razorbills will socialize in large numbers. There are two types of socializing that occur. Large groups will dive and swim together in circles repeatedly and all rise up to the surface, heads first and bills open. Secondly, large groups will swim in a line weaving across each other in the same direction.
Females lay a single egg per year. The egg is an ovoid-pyramoidal shape, ground in color and has dark brown blotches. Incubation occurs generally 48 hours after laying the egg. Females and males take turns incubating the egg several times daily for a total of approximately 35 days before hatching occurs. Razorbill chicks are semi-precocial.[18] During the first two days after hatching, the chick will spend the majority of its time under the parent’s wing. There is always one parent at the nest site while the other goes to sea to collect food for the chick. The hatchling develops a complete sheath 10 days after hatching. After 17–23 days the male parent will accompany the chick to sea.
Razorbills dive deep into the sea using their wings and their streamlined bodies to propel themselves toward their prey. While diving, they rarely stay in groups, but rather spread out to feed. The majority of their feeding occurs at a depth of 82 ft but they have the ability to dive up to 390 ft below the surface. During a single dive an individual can capture and swallow many schooling fish, depending on their size. Razorbills spend approximately 44% of their time foraging at sea. When feeding their young, they generally deliver small loads. Adults will mainly feed only one fish to their chick with high feeding deliveries at dawn and decreased feeding 4 hours before dark. Females will generally feed their chicks more frequently than males. They may well fly more than 62 mi out to sea to feed when during egg incubation, but when provisioning the young, they forage closer to the nesting grounds, some 7.5 mi away, and often in shallower water.