Above picture:  Island groups cleared of Norway Rats in the Falkland Islands

In this post, Sally Poncet continues a series on past, current and planned introduced mammal eradication projects on seabird islands around the world by writing of the many islands successfully cleared of rats in the Falkland Islands.

The First Passage Team ‘at home’ in the shearing shed on First Passage Island: back left to right: Ali Marsh, Kevin Marsh, Aidan Smith, Tom Elsby, Diane Towersey; front: Ken Passfield, Sally Poncet, Leiv Poncet; photograph by Sally Poncet

Over the past two decades, Norway Rats Rattus norvegicus have been successfully removed from 65 islands in the Falkland Islands.  The islands range in size from <1 to 2070 ha and the total area of restored land is now 6500 ha.  Another 26 islands were also cleared of rats, but within five years had been re-invaded.  With no helicopters available, the main method of bait application has been hand broadcasting.  Starting in 2001, local operators have been guided by New Zealand expert Derek Brown, whose knowledge and experience were the foundation stone for many Falklands rat eradications.  Under Derek’s tutelage, Falklands operators have acquired the necessary skills required to run their own programmes, culminating in the 2070-ha Bleaker Island rat eradication in 2019.

Derek Brown hand broadcasts rodenticide bait on 220-ha Governor Island in 2008; photograph by Helen Otley

Campaigns between 2001 and 2011 used Pestoff 20R (20 ppm brodifacoum) cereal-based pellets and Ditrac wax blocks (50 ppm diphacinone).  Subsequent operations used Bell Labs’ Brodifacoum-25W Conservation pellets that were surplus to the 2011-2015 South Georgia rodent operation.

Transporting bait in waterproof plastic buckets between islands onboard the motor yacht Golden Fleece; photograph by Helen Otley

The first multispecies eradication was completed in 2009 when Patagonian Grey Foxes Pseudalopex griseus and Norway Rats were eradicated from Tea Island (320 ha).  In 2016, House Mice Mus musculus, European Rabbits Oryctolagus cuniculus and Norway Rats were eradicated from Bense and Little Bense Islands (totalling 144 ha).

Pre- and post-baiting bird surveys associated with each of these eradications have demonstrated significant increases in bird populations once Norway Rats had been removed, and also showed that rats in some parts of the Falkland Islands regularly swim at least 800 metres and, over long periods of time and multiple incursion events, are capable of successfully colonising islands up to 1.3 km offshore.  Currently, 800 metres is considered to be the minimum ‘safe’ separation distance when assessing an island’s suitability for Norway Rat eradication in the cold waters of the Falklands.

Getting around. The yacht Peregrine at anchor at tussac-covered Big Arch Island in June 2018; photograph by Ken Passfield

With all ‘suitable’ islands in the Falklands having now been cleared of rats, there are only two left to do: Steeple Jason (House Mice) and New Island (feral cats, House Mice, European Rabbits and Black Rats R. rattus).  In comparison to Bleaker Island, the largest Falkland island cleared of rats so far, they present considerably more difficulties due to the species involved, and the fact that baiting operations would require helicopters and therefore a much larger budget than any of the operations to date (overall, our efforts so far have cost less than UK£250 000).  The feasibility of such an operation for 2270-ha New Island is currently being investigated by the island’s owner, Falklands Conservation.  If successful, the New Island Restoration Project would be by far the most outstanding for the Falklands in terms of benefits to wildlife, environmental restoration and seabird conservation.  Steeple Jason (790 ha) is owned by the Wildlife Conservation Society of New York.  It appears there are no current plans to eradicate its mice although a study suggests the prospects of eradication are promising.

Black-browed Albatrosses Thalassarche melanophris breed in large numbers on uninhabited Steeple Jason. A private nature reserve since 1970, the island is infested by House Mice; photograph by Ian Strange

Selected Publications:

Bolton, M., Stanbury, A., Baylis, A.A.M. & Cuthbert, R.[J.] 2014.  Impact of introduced house mice (Mus musculus) on burrowing seabirds on Steeple Jason and Grand Jason Islands, Falklands, South Atlantic.  Polar Biology 37:165-91668.
Brown, D. 2001.  Guidelines for Eradication of Rats from Islands within the Falklands Group. A Report to Falklands Conservation.  Stanley: Falklands Conservation.  16 pp.
Carey, P.W.  2019.  Simultaneous rat, mouse and rabbit eradication on Bense and Little Bense Islands, Falkland Islands.  In: Veitch, C.R., Clout, M.N., Martin, A.R., Russell, J.C. & West, C.J. (Eds). Island Invasives: Scaling up to meet the Challenge.  Proceedings of the International Conference on Island Invasives 2017Gland: IUCN.  pp. 108-113.
Matias, R & Catry, P. 2008.  The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirds.  Polar Biology 31: 609-616.
Poncet, S., Passfield, K., Kuepfer, A. & Tabak, M.A. 2019.  The effect of Norway rats on coastal waterbirds of the Falkland Islands: a preliminary analysis.  In: Veitch, C.R., Clout, M.N., Martin, A.R., Russell, J.C. & West, C.J. (Eds).  Island Invasives: Scaling up to meet the Challenge.  Proceedings of the International Conference on Island Invasives 2017.  Gland: IUCN.  pp. 147-153.
Poncet, S., Poncet, L., Poncet, D., Christie, D., Dockrill, C. & Brown, D. 2011.  Introduced mammal eradications in the Falkland Islands and South Georgia – Management.  In: Veitch, C.R.; Clout, M.N. & Towns, D.R. (Eds).  Island Invasives: Eradication and Management. Proceedings of the International Conference on Island Invasives.  Gland: IUCN & Auckland: Centre for Biodiversity and Biosecurity.  pp. 332-336.
Quillfeldt, P., Schenk, I., McGill, R.A.R., Strange, I.J., Masello, J.F., Gladbach, A., Roesch, V. & Furness, R.W. 2008.  Introduced mammals coexist with seabirds at New Island, Falkland Islands: abundance, habitat preferences, and stable isotope analysis of diet.  Polar Biology 31: 333-349.
Rexer-Huber, K., Parker, G.C., Reeves, M., Stanworth, A.J. & Cuthbert, R.J. 2013.  Winter ecology of house mice and the prospects for their eradication from Steeple Jason (Falkland Islands).  Polar Biology 36: 1791-1797.
Tabak, M.A., Poncet, S., Passfield, K. & Martinez del Rio, C. 2015.  Modeling the distribution of Norway rats (Rattus norvegicus) on offshore islands in the Falkland Islands. NeoBiota 24: 33-48.


Sally Poncet, Stanley, Falkland Islands, 21 March 2023