Several species of seabirds have shown alarming declines over the last thirty years. Most pronounced is the Manx Shearwater which declined from some 3000 in 1972 to the verge of extinction in 2004.

Shags have also declined by almost a half in the last 10 years and Razorbills to a quarter of their former numbers. Only the Black-legged Kittiwake has maintained its numbers and even increased over this period. The full report from the Highland Ringing Group can be downloaded here.

The main cause of the declining seabird populations is believed to be predation by the introduced population of Brown Rats that live on the islands. Burrow-nesting seabirds (such as the Manx Shearwater) are particularly vulnerable and were the first to suffer.

Puffins nest mainly on inaccessible stacks and have been less affected. Even large birds, such as Shags, have been affected and are virtually extinct at Garisdale and the Nunnery, hanging on mainly on the inaccessible cliffs at Geugasgor. Kittiwakes typically nest on particularly inaccessible cliffs and have been unaffected.

A major programme to eradicate rats from the islands is currently underway.