THE COMMON GUILLEMOT

Stora Karlsö hosts the Baltic Sea’s largest colony of guillemots; just over 20,000 breeding pairs. Together with their offspring, they make up about three-quarters of the entire Baltic Sea guillemot population!

In early May, the female lays her single egg directly on the cliffs. A narrow ledge 40 meters up in the air might seem somewhat precarious, but the guillemot wedges the egg firmly between her legs, its oval and pointed shape means that it is in fact reasonably safe. Even though some eggs do fall into the abyss, not least when things heat up between neighbours! Both parents alternate between brooding the chick and foraging for food. The youngster craves continual feeding with small fish, mainly sprat, that the parents sometimes pick up miles out at sea. But all this flying back and forth costs far too much parental energy. When the chick is about three weeks old the small guillemot chicks jump from the cliff ledges straight out into the shimmering summer night, bouncing hard on the rocky beach forty metres below before reuniting with their fathers out at sea.
At the beginning of August, the guillemot ledges gape empty and silent. The birds have left their nesting places and returned to the open sea where they belong.

Scientific name: Guillemot (Uria aalge)
Genus: Uria
Family: Alcidae – alkor
Size: 40-45 cm high and with a wingspan of 60-70 cm
Lifetime: about 30 years, but the record is 46 years
Sexual maturity: At age 4-5 years
Incubation: The female lays a single egg in May June, and the incubation period is 30 days, during which time the male and female help and relieve one another .
Song: a repetitive nasal ”wha-wha-wha”, transitioning into a lowing sound.
Feeding: Small fish, in the Baltic Sea mainly sprat and herring.
Baltic population : Around 80,000. Of these approx. 50,000 breeding adults, as well as approx. 20,000 chicks and 10,000 young birds.

Distribution
The guillemot lives mostly out to sea but breeds and hatches on land on Sweden’s east coast, as well as around Gotland (Karlsöarna), the coast of Västerbotten, Uppland and Södermanland. The island of Boden off the coast of Västerbotten is the northernmost colony.