Largest super-colony of puffins
Iceland ()

Based on “apparently occupied burrows”, or AOBs (the standard measurement unit for assessing puffin populations), the largest aggregation of Atlantic puffins (Fratercula arctica) currently occurs in Vestmannaeyjar (aka the Westman Islands; 63.4°N 20.3°E) located off south-west Iceland. According to recent estimates, the archipelago hosts some 830,000 breeding pairs – approximately 20% of the world population of this species – during the April–August nesting season.

Here, a “super-colony” is defined as a conglomeration of smaller puffin sub-colonies found in one locality that, although may be spread over several small islands, still share the same foraging area.

Historically, the largest puffin super-colony occurred in Røst (67.5°N 12.0°E) at the outermost end of the Lofoten archipelago off north-west Norway. In 1979, it was estimated to be home to 1.4 million breeding pairs, but this had shrunk to approximately 270,000 AOBs as of 2019. Approximately 98.5% of the puffins inhabit five islands positioned in a 9-km-long (5.5-mi) line in the outer part of the island group, with the remaining 1.5% on 12 small islets spread in between the five larger sub-colonies.

Atlantic puffin numbers have been in decline for many years owing mostly to reduced levels of their preferred food, in some areas probably also suffering from oil spill events and a rise in extreme weather events. These environmental changes have been exacerbated by these birds’ low rate of reproduction and limited nesting locations.

The full range of the Atlantic puffin extends from northern Greenland (Denmark), Newfoundland (Canada) and Maine (USA) in the west, to north-west Russia in the east and as far south as Spain’s Canary Islands (in winter).