The rat cull: saving South Georgia’s seabirds

Drygalski Fjord, South Georgia

Killer rats

The spread of humans to even the most remote Antarctic islands – where they settled to hunt seals and whales – was followed by the spread of an unexpected predator, the brown rat, Rattus norvegicus. Many Antarctic seabirds, evolved to breed in islands where they were free from land predators, are defenceless against rats, which eat the bird’s eggs and chicks. Global populations of most Antarctic seabirds are declining, and so authorities are resorting to culling rats in the islands where these birds breed1.

The island of South Georgia, in the South Atlantic, is one of such breeding sites. Millions of birds, including penguins, albatrosses, petrels and prions, are based in the island’s rugged, icy shores 2. Visitors may think that their numbers are huge, but they are nothing compared to what they were before rats were introduced in the 18th century by sealers and whalers. Rats do not attack penguins and albatrosses, which are big enough to defend themselves, but they do cause huge harm to most other birds.

Making South Georgia a rat-free (and largely human-free) nesting site would increase the global long-term chances of survival of many of these birds. Removal of rats would also save the indigenous South Georgia pipit, the only songbird in the Antarctic, which is now extinct in most the island, except for the small remaining rat-free areas2.

Rattus norvegicus 1

Rattus norvegicus, the Brown Rat.

The big cull

South Georgia Heritage Trust decided to run a programme of rat eradication, named the Habitat Restoration Project. The first phase, done between 2010 and 2011, at a cost of £1.6 million pounds, was successful3. Using two helicopters, a team spread around 50 tonnes of rat-specific poisonous bait throughout part of the island, treating a total of 128km2. This was the largest area an eradication programme ever targeted. Millions of rats were killed, and none has been seen in the targeted area since.

Key to this success is the fact that South Georgia is criss-crossed with glaciers, which rats cannot cross. The glaciers divide the island into independent areas, which the team can deal with one by one. Without the glaciers, it would have been extremely difficult to target such a large island.

Southgeorgiapipit

Anthus antarcticus, South Georgia Pipit

This week, the Trust announced that it would go on with the second phase of the programme, which will see all rats in the island killed by 2014. The stakes are high, as eradication attempts are many times not successful. For example, five out of ten attempts of culling rats in different islands of the Galapagos failed4. The problem is that it’s very difficult – and expensive – to kill every single rat in such a large area (and it only takes a pregnant female to repopulate a whole island).

It’s very unlikely that the operation would be repeated in case it fails, considering the whole programme will cost around £8 million in total – and that climate change is set to melt the glaciers that make the whole thing possible in the first place. To make sure no rat escapes, monitoring will continue long after the cull is over.

Giant petrel flies at soutg georgia

A giant petrel (genus Macronectes) flying over South Georgia

What happens next?

Even if the programme is successful, a visiting ship could introduce rats into the island again. Anyone who has visited Australia or New Zealand knows the draconian care taken by customs to prevent accidental introduction of alien species in those countries. The Government of South Georgia is imposing similar measures on the island5. Co-operation with the local fishing industry and tourist cruises, the main visitors to the island, is essential for this to be successful. The danger of not involving people with local interests is exemplified by an extreme case in the Galapagos, where a few fishermen threatened to re-introduce eradicated goats on the islands because they were not happy about fishing permits4.

And obviously, it will be really important to monitor the local bird species and to see if their populations actually increase after the rat culling is finished. Killing rats in the millions is not without ethical implications, particularly considering that only humans can be blamed for their introduction in the first place. Culling can only be justified if it does have a very positive impact on the local bird species. It is too early to tell if any of the birds are doing better. Certainly, the culling will have to be followed with a programme of bird population monitoring and of comprehensive conservation action. This is the only way to ensure the bird’s survival in the long term.

If in a few years time, a visitor to South Georgia hears the pipit’s song, the programme will doubtlessly have been successful.

Wandering Albatross on South Georgia

Wandering Albatross Diomedea exulans on South Georgia

Written by Roddy Pracana, a student at the MRes BEC.

References

1. Croxall, J. P., Butchart, S. H., Lascelles, B., Stattersfield, A. J., Sullivan, B., Symes, A. N. D. Y., & Taylor, P. H. I. L. (2012). Seabird conservation status, threats and priority actions: a global assessment. Bird Conservation International, 22(1). here

2. Poncet, S. (2006) South Georgia and the South Sandwich Islands. In Sanders, S. (Ed.).. Important Bird Areas in the United Kingdom Overseas Territories. RSPB. Retrieved December 1, 2012, from http://www.sgisland.gs/index.php/(d)Birds

3. South Georgia Heritage Trust (2008) Environmental Impact Assessment for the eradication of rodents from the island of South Georgia. Online. Retrieved on December 1, 2012, from http://www.sght.org/newsletters-and-publications

4. Carrion, V., Donlan, C. J., Campbell, K. J., Lavoie, C., & Cruz, F. (2011). Archipelago-wide island restoration in the Galápagos Islands: Reducing costs of invasive mammal eradication programs and reinvasion risk. PloS one, 6(5), e18835. here

5. The Government of South Georgia and South Sandwich Islands (2012) South Georgia and South Sandwich Islands Biosecurity Protocols. Online. Retrieved on December 1, 2012, from http://www.sgisland.gs/index.php/(d)Biosecurity?useskin=edu

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