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Bait station locations - Canna Seabird Recovery Project
Bait station locations - Canna Seabird Recovery Project
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The seabird populations on Canna have been studied since 1969 by volunteer members of the Highland Ringing Group. During the 1970s and 1980s many species, particularly shags, auks and gulls underwent large increases in breeding numbers, with the shag colony becoming one of the largest in Europe. Numbers were so high that the island was declared a Special Protection Area (SPA) for its seabirds, part of the European Union Natura 2000 network of protected sites.

In the late 1980s and through much of the 1990s seabird numbers began to decline. Research by the Highland Ringing Group and the National Trust for Scotland showed that high levels of predation by introduced brown rats (Rattus norvegicus) were affecting seabird breeding success and resulting in the birds abandoning traditional breeding areas on the island.

The first decline involved the Manx Shearwater colony, which showed a drastic drop in numbers from 1,500 pairs recorded during the 1980s. These birds nested in burrows along the Tarbert road, just west of the human inhabited part of the island. The decline was linked with a marked drop in breeding success, due to increased levels of predation. By 2005, perhaps only 1 or 2 pairs of shearwaters survived in isolated areas on some of the more inaccessible cliffs.

The Canna shag colony peaked at 1753 apparently occupied nests in 1984. Formerly there were four large sub-colonies, two in the western half of the island at Garrisdale and the Nunnery, one in the east at Lamasgor and one in the north at Geugasgor. The Nunnery colony was the first to decline dropping from 121 nests in 1997, mostly located under boulders on the raised wave cut platform, to only 21 nests in 2005, all located on inaccessible narrow cliff ledges. Lamasgor saw a similar decline from 231 nests in 1998 to 45 in 2005. Garrisdale then followed dropping rapidly from 221 nests in 2001 to only 18 in 2005. Finally Geugasgor is beginning to follow the pattern dropping from 336 nests in 2003 to only 167 in 2005.

Not all colonies were declining. On Sanday and at Rhu Langanais birds started nesting on inaccessible ledges on cliffs and in caves. It appeared that a redistribution was taking place with birds deserting traditional boulder areas, where they were easily susceptible to predation from rats and moving to more inaccessible sites but this was insufficient to stem the overall decline.

It was decided that to stop and ultimately reverse the dramatic decline in seabird numbers on the Canna SPA it would be necessary to eradicate all the rats from the island. Funding was provided from the EU Life Nature Fund, with matching amounts from Scottish Natural Heritage and the National Trust for Scotland, owners of Canna.

Funding was approved in 2005 and a contract was awarded to Wildlife Management International Ltd from New Zealand. Work started in late August and early September with a team of eight WMIL staff, backed up by up to eight volunteers.

The first task was to establish and mark a grid of 4388 bait stations.

Each bait station was then loaded with ten wax blocks containing the rodenticide, Diphacinone. This was chosen as it significantly reduces the risks of secondary poisoning, which might have affected Canna’s important bird of prey populations. The bait was checked and replenished every three days to monitor for consumption by rats, bait take being recorded for each station and plotted on digital maps to record progress. By March 2006 no further bait take was recorded and it was believed that all rats on the island were dead. This was confirmed by two years of continuous monitoring, using unpoisoned wax blocks impregnated with chocolate. The island was officially declared rat-free in 2008 by Environment Minister Mike Russell.


Subsequent monitoring of seabirds has shown that Shearwaters have returned to breed successfully in small numbers in their former colony and that Shags and puffins have begun to increase.

Quarantine and contingency measures have been introduced to ensure that rats do not return to recolonise the island.

A description of the project can be found by downloading the summary report or full report below:

Summary Layman's Report 

Technical Final Report

Appendices 

Funding was provided by the EU LIFE Nature programme with additional support from Scottish Natural Heritage, the National Trust for Scotland and the Royal Zoological Society of Scotland.
covering the entire island. 

 

History of the Highland Ringing Group work on Canna

To find out more, click here