Sea birds returning to Canna

06/03/2007 00:00:00 Since the pest eradication project run by the National Trust for Scotland (NTS) on the island of Canna, the seabird population is showing signs of recovery.

A survey carried out by the Highland Ringing Group shows that the number of key species, especially shags, razorbills and Manx shearwaters, appears to be on the road to recovery.

Razorbills, which nest amongst boulders and are especially vulnerable to rat predation, have shown a ten fold increase from just 27 successful nests in 2005 to 273 this year. This reverses a long-term decline which saw numbers decline from 440 in 1995.

Shags were also badly hit but, at one colony, numbers are up from just 48 pairs in 2005 to 72 pairs this year. More importantly, the average number of chicks successfully reared is up from 0.7 per nest to 1.2.

Canna used to be the home for one of the largest colonies of shags anywhere in Europe but numbers had declined by over 40%. The first nests to suffer were those in accessible boulder fields around Garrisdale, the Nunnery and Lamasgor (areas of Canna), with the birds retreating to the more inaccessible ledges. Recovery in the boulder fields has been particularly noticeable. The Manx shearwater colony, estimtaed to have been as large as 1500 pairs, was completely destroyed. The use of tape recordings of Manx shearwater calls revealed that birds have come back to some of the burrows of the former colony, last used in 1999, and that other birds may be present around the island.

Abbie Patterson, National Species Recovery Officer at the NTS, said: 'While it will take a long time for seabird numbers to build back up to their previous levels, it is encouraging to see that the long term decline has been halted and that numbers of vulnerable species have begun to increase once more.' Canna is owned by the National Trust for Scotland. Research showed that a rise in Brown rat numbers, probably due to milder winters, led to a sharp increase in predation on the island's seabirds.

A programme to eradicate all rats from the island was initiated. The last known rat was detected and poisoned in mid February 2006. Click here to see full details of the Rat extermination programme.

A monitoring grid of 1000 feeding stations is checked regularly, and so far there has been no sign of any rats on the island.

A part of the project involved removing some native wood mice, which may be unique to the island. The Royal Zoological Society of Scotland took 154 mice to Edinburgh Zoo and Highland Wildlife Park for safe keeping and to breed in captivity. Some of these mice have now been returned to Canna.