Common guillemots or Murre (Uria aalga) are the most numerous of the birds we see ‘nesting’ on the Treshnish Isles with around 10,000, primarily on Lunga and especially huddled close on the Harp Rock. The sound of the general squabbling and kerfuffle of many thousand birds jostling for position can be heard a significant distance away during the height of the breeding season.
Guillemots, as members of the alcidae or auk family, are related to both the inquisitive and engaging razorbill and the ubiquitous puffins with whom they share an island home. The vast bulk of Treshnish Isles guillemots are to be found nesting on Harp Rock (Dun Cruit) roughly from early May until they move back off onto the water by the end of July. They lay conically shaped (pyriform), eggs, often on the most impossibly sloped cliff edges and one theory suggests the pointy shape is simply to avoid the eggs rolling off the edge given their tight ‘rolling circle’! The eggs, as seen below, are a greenish blue colour and are mottled with dark markings.
Altogether it is estimated that a little under a million pairs breed around the coasts of the UK. The RSPB list their conservation status as ‘amber’.
Many of the common guillemots we see are of the ‘bridled’ variety. There are virtually none of these ‘bespectacled’ birds further south in Europe, with the percentage increasing in the colonies progressively heading north. In Iceland apparently 70% have this particular mutation, which is only apparent during the breeding season.