This is an egg of the European Shag (Phalacrocorax aristotelis), a coastal seabird belonging to the family Phalacrocoracidae (cormorants and shags).

Shag eggs are typically elongate-oval in shape, measuring approximately 5.9–6.5 cm in length and 3.6–4.0 cm in breadth. Freshly laid eggs are pale blue, but are characteristically covered by a chalky white calcareous coating. This outer layer often becomes stained brown or grey during incubation due to contact with nesting material and the birds’ feet.

Location:
European Shags breed along rocky coastlines and offshore islands of the northeast Atlantic, including the coasts of the United Kingdom, Ireland, and parts of western Norway and France. Nests are typically placed on cliff ledges, in crevices or within caves, often in relatively small colonies.

Average Size:
Length: ~5.9–6.5 cm.

Breadth: ~3.6–4.0 cm.

Family:
Phalacrocoracidae (cormorants and shags)

Species:
Phalacrocorax aristotelis

Ecological Role:
European Shags are pursuit divers, feeding primarily on small fish such as sandeels. Their breeding colonies contribute nutrients (via guano) to cliff and island ecosystems, supporting specialised plant and invertebrate communities.

Movement and Behaviour:
This species is largely coastal, with limited seasonal dispersal. It is a strong diver, using its feet to propel itself underwater. During the breeding season, adults commute between feeding grounds and nest sites to provision their young.

Reproduction & Eggs:
Nests are constructed from seaweed, grasses and other vegetation, forming bulky platforms on rocky ledges or sheltered cliff sites. A typical clutch consists of 2–4 eggs. The eggs’ chalky coating helps protect them from moisture and abrasion in damp coastal environments. Both parents share incubation duties, which last approximately 27–31 days. Chicks hatch relatively undeveloped and are highly dependent on parental care, developing flight feathers and muscles after about 7–8 weeks.

Conservation Status:
Globally assessed as Least Concern by the International Union for Conservation of Nature (IUCN), although populations can be affected by oil pollution, changes in prey availability and severe weather.