Bell, E.; D. Boyle, K. Floyd, P. Garner-Richards, B. Swann, R. Luxmoore, A. Patterson, and R. Thomas. The ground-based eradication of Norway rats (Rattus norvegicus) from the Isle of Canna, Inner Hebrides, Scotland The ground-based eradication of Norway rats (Rattus norvegicus) from the Isle of Canna, Inner Hebrides, Scotland E. Bell1, D. Boyle1, K. Floyd1, P. Garner-Richards1, B. Swann2, R. Luxmoore3, A. Patterson4, and R. Thomas5 1Wildlife Management International Limited, 35 Selmes Road, Rapaura, RD3, Blenheim, 7273, New Zealand. <[email protected]>. 214 St Vincent Road, Tain, Ross-shire, IV19 1JR, Scotland. 3Scotland. National Trust for Scotland, 28 Charlotte Square, Edinburgh, EH2 4ET, Scotland. 4ABI Wildlife Consultancy, 4 Carnbee End, Edinburgh, EH16 6GJ, Scotland. 5The Royal Zoological Society of Scotland, 134 Corstorphine Road, Edinburgh, EH12 6TS, Scotland. Abstract: Seabird populations, particularly European shags (Phalacrocorax aristotelis) and Manx shearwater (Puffinus puffinus), on the Isle of Canna have been in decline for several years. Norway rats (Rattus norvegicus) were identified as the most likely factor. The Canna Seabird Recovery Project, developed as a result of this information, was a three year project incorporating the ground-based eradication of Norway rats (Phase I) followed by long-term monitoring, quarantine and contingency for rodents (Phase II) and continued long-term monitoring of the seabird populations (Phase III). The National Trust for Scotland (NTS) contracted Wildlife Management International Limited to direct the first and second phases of the project (August 2005-June 2008), with the assistance of NTS staff and volunteers. Techniques, problems, non-target species, (particularly wood mice (Apodemus sylvaticus) and white-tailed eagles (Haliaeetus albicilla)) issues, solutions and results of the operation on the permanently inhabited island are covered. Bait stations with cereal-based wax blocks containing diphacinone at 0.005% w/w were established on a fifty to one hundred metre grid over the island. Some offshore islets harboured rats, although some of the more sheer stacks did not. Interference with bait stations by non-target species was moderate to high, and bait stations required extra strengthening or protection to prevent damage or disturbance by cattle (Bos taurus), ponies (Equus caballus), sheep (Ovis aries), rabbits (Oryctolagus cuniculus) and hooded crows (Corvus corone cornix). Monitoring confirmed the successful eradication of rats from the Isle of Canna in June 2008. This provides another example of the effectiveness of ground-based rodent eradication techniques and provides an opportunity to restore the seabirds. Keywords: Wood mouse, white-tailed eagle, diphacinone, monitoring, quarantine and contingency INTRODUCTION The Isle of Canna is located off the west coast of STUDY AREA AND METHODS Scotland in the Inner Hebrides (6o30’W, 57o03’N), and consists of two semi-connected main islands; Canna (1126 Canna and Sanday are naturally joined at low tide and ha) and Sanday (191 ha), and several small offshore stacks are now linked by a road bridge. Canna is approximately 8 and islets (Fig. 1). The Highland Ringing Group, which km long, east to west, and 2 km across at its widest point. has monitored the seabird colonies of the Isle of Canna for over 40 years had recorded that seabird populations (in particular razorbills (Alca torda), European shags (Phalacrocorax aristotelis) and Manx shearwater (Puffinus puffinus)) had been declining since the early 1990s (Swann 2002). Brown (Norway) rats (Rattus norvegicus) were identified as the most likely factor influencing this decline, from the observed increased predation on eggs and chicks (Swann 2002). Rats are known to have devastating effects on seabird populations, causing extinctions of birds on numerous islands throughout the world (Moors and Atkinson 1984; Atkinson 1985; Jones et al. 2008). Many islands have been successfully cleared of rats (Thomas and Taylor 2002; Howald et al. 2007) with a subsequent increase in bird populations (Towns and Broome 2003; Jones et al. 2008). The National Trust for Scotland (NTS) commissioned a feasibility study into the potential for the eradication of rats from Canna (Bell and Bell 2004), based on an earlier proposal (Patterson 2003). The Canna Steering Group, a partnership of NTS, Edinburgh Zoo, Scottish Natural Heritage (SNH), the Joint Nature Conservation Committee (JNCC) and Royal Society for the Protection of Birds (RSPB), decided that eradication of rats using a ground-based eradication technique was to proceed. Wildlife Management International Limited (WMIL) won the tender to direct the eradication with the assistance of NTS volunteers and staff. The three-phase Canna Seabird Recovery Project (Phase I eradication of Norway rats; Phase II monitoring for surviving rats and implementation of quarantine and contingency procedures; Phase III long- term monitoring of seabirds) began in August 2005 (Bell et al. 2006). Complete details of the project are available on Fig. 1 Location of Isle of Canna, Inner Hebrides, the project website (www.ntsseabirds.org.uk). Scotland. Pages 269-274 In: Veitch, C. R.; Clout, M. N. and Towns, D. R. (eds.). 2011. Island invasives: eradication and management. IUCN, Gland, Switzerland. 269 Island invasives: eradication and management With the exception of the in-bye land close to the farmhouse or from an early shipwreck. Only the Norway rat is known and buildings, Canna rises steeply from beach platforms on from the island and previous surveys recorded them in all all sides to a rolling plateau with the highest point at 210 m habitat types (Patterson and Brough 1999; Patterson and above sea level. Sanday is approximately 3 km long, east to Lloyd 2000; Patterson and Quinn 2001; Patterson 2003). west, and just over 1 km at its widest point. Sanday reaches Distribution, however, was not uniform with the highest 59 m a.s.l., but is similar to Canna with steep coastal cliffs, densities occurring around the in-bye land, the shoreline beach platforms and a low rolling plateau. and coastal slopes; a pattern common to most island Owned and managed by NTS, the Isle of Canna has situations where rats are dependent on foraging for food 15 permanent residents who maintain the farm and crofts, in inter-tidal zones and at seabird colonies. Other notable or manage the tourism ventures. The islands (i.e. both rat presence on the island was generally related to farming Canna and Sanday) are popular with visitors interested in activity, watercourses and rabbit habitat (Patterson 2003). the seabirds, raptors, flora and history. There are several The eradication option adopted for this project was a houses, crofts, farm buildings, churches, a lighthouse and ground-based poison programme using protective bait school. Canna has a jetty and is regularly serviced by the stations to reduce risk to non-target species, particularly Caledonian MacBrayne ferry from Mallaig. the white-tailed eagle and other raptor populations. The The islands are covered by maritime heath, coastal programme ran from 25 August 2005 to June 2008 and pasture and heather moorland, apart from Tarbert and in- included bait station establishment, capture of wood bye areas, which are improved pasture. There are also mice, poisoning, monitoring, quarantine and contingency, small areas of mixed woodland adjacent to the in-bye and a final check and rat-free declaration (Table 1). land. The island is grazed by domestic livestock including Each operational task was undertaken and completed as horses (Equus caballus), sheep (Ovis aries), and cattle follows: (Bos taurus); three feral goats (Capra hircus), and rabbits (Oryctolagus cuniculus). Canna also has three other small Bait station grid mammals; the pygmy shrew (Sorex minutus), house mouse The bait station grid was established between 3 (Mus musculus) and wood mouse (Apodemus sylvaticus). September and 27 October 2005. Bait stations were made Hedgehogs (Erinaceus europaeus) are also present. A from 750 mm lengths of 100 mm diameter corrugated small number of domestic cats and dogs are kept by the plastic drainage pipe, pegged to the ground with wire residents. “legs” to prevent movement by wind and/or stabilised with The Isle of Canna (excluding all the in-bye land) was rocks or other material to reduce interference by sheep, designated a Site of Special Scientific Interest (SSSI) in cattle, and ponies. Additional wires pushed through both 1987 for its biological and geological features. Following entrances reduced the entrance size to exclude smaller this, Canna was also designated in 1997 as a Special non-target species such as rabbits, hooded crows (Corvus Protected Area (as part of the European Union NATURA corone cornix) and gulls and to help secure the station to 2000 network of important bird sites) for its internationally the ground. Both entrances were raised slightly off the important concentrations of breeding seabird species. ground to deter entry by insects. Shags, razorbills, kittiwakes (Rissa tridactyla), puffins Bait was placed in the centre of the station through (Fratercula arctica), guillemots (Uria aalge), black a small access hole cut in the top which was covered by guillemots (Cepphus grylle) and fulmars (Fulmarus an additional short clip-on section of pipe as a lid. “Crow glacialis) all breed on the island. However, many of these clips” (a piece of wire across the station), as used during species are now in decline (Swann 2001, 2002). Historically, the Lundy Island rat eradication (Bell 2004), were also Manx shearwaters were also recorded to breed on the used to prevent crows from removing lids to access bait. island, but have declined to almost zero (Swann 2002). Bait stations were placed on a 50-metre grid on the Two pairs of white-tailed eagles (Haliaeetus albicilla) and coastal slopes and cliffs, the in-bye area and on Sanday a pair of golden eagle (Aquila chrysaetos) breed on the Isle (Fig. 2). On the higher plateau areas on Canna, stations of Canna, along with buzzards (Buteo buteo), peregrines were placed more widely at 100 m (Fig.