Of 121 important bird areas in Iceland, 70 of these are seabird colonies. Many seabird populations in Iceland are large in an international context. Knowledge of these populations is also fairly good in many cases, and it is generally easier to demarcate the boundaries of seabird colonies than other important bird areas.
All seabird colonies are important breeding sites. The better part of the populations of 15 of 24 Icelandic bird species – frequently 100% or the entire regional population – use these colonies to breed, including all large seabird populations in Iceland with the exception of the Arctic tern (Sterna paradisaea). Delimitation of important Arctic tern colonies has been complicated by the population crash in recent years.