In 1998 the Countryside Council  for Wales (CCW) and the Royal Society for the Protection of Birds (RSPB) eradicated rats from Puffin Island in order to improve the habitat of nesting seabirds.

  • Puffin Island, (Ynys Seiriol / Priestholm): 32 hectares of carboniferous limestone capped with glacial drift and guano. 
  • Dense vegetation of rank grassland and elder (Sambucus nigra) scrub. 
  • 500 metres off the eastern tip of Anglesey at low tide
  • Site of Special Scientific Interest (SSSI) and Special Protection Area, (SPA) for breeding cormorant - the largest in Britain with over 750 pairs -36% of the Welsh population
  •  Other breeding seabirds: puffin, guillemot, razorbill, oystercatcher, shag, fulmar, kittiwake, herring gull, greater black backed gull and lesser black backed gull.[1]
Puffin Island / Ynys Seriol.
Puffin Island / Ynys Seiriol © J B Ratcliffe
Cormorant (Phalacrocorax carbo). Copyright J B Ratcliffe 1990
Cormorant (Phalacrocorax carbo) © J B Ratcliffe
  • The iconic puffins attract thousands of tourists each year
  • 1804: estimated in excess of 50,000 puffins –“young birds are pickled by the renters of the island and form an article of traffic peculiar to this neighbourhood”[2]
  • 1907 “at least 2000 puffins” [3]
  • By the 1990s numbers had probably dwindled to less than 20 pairs.

Brown rats (Rattus norvegicus)

  • First recorded in Anglesey in 1762 "eating the corn while men were still reaping it"
  • Recorded on Puffin island following a shipwreck in 1816
  • Estimated 500,000 rats with perhaps 250,000 burrows (Sunday Times, 4 April 1971). Journalistic license, but indicates the scale of the problem.
Puffin (Fratercula arctica). Copyright J B Ratcliffe 1990
Puffin (Fratercula arctica) © J B Ratcliffe
       Other mammals:
  • Rabbits, eradicated by myxomatosis in 1955
  • Regularly 100+ Atlantic grey seal
  • No other mammals recorded [4]
  • Uninhabited since the abandonment of 6th century monastery and University of Liverpool marine biological summer field station (1888 - 1897).


  • The restoration of a ground-predator free seabird colony.

Helicopter delivery of second tonne of bait. Copyright: J B Ratcliffe1998
Delivery of warfarin bait © J B Ratcliffe


  • Boat access difficult and weather dependent, therefore conventional re-baiting routine impossible.
  • No history of warfarin exposure therefore little chance of resistance
  • Warfarin offers lowest risk to other species through secondary poisoning
  • Diphenocoum chosen for follow-up operation when numbers of carcases (and secondary poisoning) would be minimised.
  • February 1997 & Jan 1998, reconnaissance with fat-soaked chew sticks to establish extent of rats – ubiquitous.


  • February & March 1998, 2.5 tonne of 0.05% warfarin wheat bait supplied by boat, (and later helicopter) applied as 500g down burrows.
  • January 1999, Diphenocoum bait in 100g pre-packed sachets housed in 300mm plastic drainpipe sections, placed at 88 locations, especially the cliff zone, to establish a monitoring programme with rebait points if required.
  • An additional 40, 600mm baited tubes located at locations where loss of bait might be attributed to gulls.
  • All tubes removed from the island in late 2000.
  • Chew sticks (wooden sticks soaked in fat) used to monitor presence / absence of rats.
Application of diphenocoum bait January 1999. Copyright: J B Ratcliffe 1999
Baiting with diphenocoum. © J B Ratcliffe


  • Huge media interest – radio, television and press – public and corporate accolades.
  • No evidence of rats since 1998.
  • No animal welfare complaints.
  • Little conclusive change in puffin numbers.
  • Continuing increase in guillemot numbers, pre-dates rat eradication.
  • Re-establishment of breeding black guillemot
  • Possible establishment of breeding eider
  • No significant change in cormorant (SSSI & SPA feature)
  • Increase in grass thatch, bramble and elder scrub ….
  • Rat eradication is a speculative investment. The outcome is not guaranteed, at least in the short term.
  • Other factors also influence seabird success.
  • Vegetation management (grazing) may also be required to optimise conditions for target seabird species. Such intervention would raise the question of whether to pursue “natural” island conditions or emulate traditional management.
  • At least 200 man-days (inc. volunteers) labour.
  • Management of the key SSSI & SPA “feature” (cormorant) did not require this. How do we justify this investment against other conservation priorities?
  • Perhaps this is a tourism issue rather than a conservation issue!


The project was a partnership of CCW and RSPB, with assistance from the Baron Hill Estate, Sorex Ltd and 22 Squadron RAF VAlley. Dr Richard Arnold (University of Wales, Bangor), Dr Bernard Zonfrillo (Glasgow University) and Dr Alan Buckle (Zeneca plc) advised.


1. Arnold R (2001) A history of the birds of Puffin Island, in P Hope Jones & P Whalley (2004) Birds of Anglesey. Menter Mon Llangefni.

2. Bingley W (1804) North Wales including its scenery, antiquities, customs and some sketches of its natural history delineated from two excursions though all the interesting parts of that Country during the summers of 1798 and 1801. 2Vols. Longman & Rees,, London

3. Forrest, H. E. (1907). The Vertebrate Fauna of North Wales. Witherby & Co. London

4. Healing  T  D (1997)  Small mammals of the Welsh Islands, pp P M Rhind, T H Blackstock & S J Parr (eds) 1997. Welsh Islands, ecology conservation and land use. Countryside Council for Wales. Bangor