 St Kilda is a breeding ground for many important seabird species . One of the world 's largest colonies of northern gannets , totalling 30 @,@ 000 pairs , amount to 24 percent of the global population . There are 49 @,@ 000 breeding pairs of Leach 's petrels , up to 90 percent of the European population ; 136 @,@ 000 pairs of Atlantic puffins , about 30 percent of the UK total breeding population , and 67 @,@ 000 northern fulmar pairs , about 13 percent of the UK total . Dùn is home to the largest colony of fulmars in Britain . Prior to 1828 , St Kilda was their only UK breeding ground , but they have since spread and established colonies elsewhere , such as Fowlsheugh . The last great auk ( Pinguinus impennis ) seen in Britain was killed on Stac an Armin in July 1840 . Unusual behaviour by St Kilda 's bonxies was recorded in 2007 during research into recent falls in the Leach 's petrel population . Using night vision gear , ecologists observed the skuas hunting petrels at night , a remarkable strategy for a seabird . 
