The endangered Henderson petrel.
Credit: Richard Cuthbert; RSPB
~ Anthony King
Just to challenge myself, I’m writing this blog on the day Wikipedia is blacked out. It could be worse. If your species evolved for island living, be scared. Three-quarters of all known extinctions have happened on islands. Forty-three bird species on the Hawaiian Islands are known from recent 'fossils', having vanished in the centuries between the arrival of the Polynesians and Captain Cook’s sojourn in 1778.
Often it is the species we bring with us that inflict most damage. On Guam, not a single native bird survived the reptilian onslaught unleashed when brown tree snakes came ashore sometime during the Second World War. Puffin Island off Wales was chock-full of colourful seabirds in 1774, when puffins were likened to "a swarm of bees". Anthropomorphising, I imagine the bemusement of clownish puffins on first catching sight of twitching whiskers and the little furry newcomers. By 1835, the last puffin gave up the ghost and had surrendered Puffin Islands to the rats.
Manx shearwaters were named for their vast numbers on an island off the Isle of Mann in the Irish Sea. It was said that a Viking fleet preparing to invade Dublin in 1014 was initially 'attacked' by so many shearwaters that the sailors had to protect themselves with swords and shields. A tall tale, perhaps; shearwater resistance proved futile when brown rats invaded their island around 1780, wiping the colony out in 20 years. Often a shipwreck delivers these deadly mammals.
With such an infamous history, I cheered some recent news from the Pacific. An operation against the rodents of Henderson Island in the south Pacific Ocean began last May when the MV Aquila left Seattle. It rendezvoused at Somoa to pick up 76 tonnes of rat poison and arrived at Henderson in August. Two helicopters were launched from the ship to drop the rodenticide over the island, using GPS technology to ensure a deadly spread.
Henderson Island is home to 55 unique species, including four species of land bird. The rats had set to work though, gnawing away at the island’s conservation credentials. They killed over 25,000 Henderson petrel chicks a year, pushing the species toward extinction. Seabirds had dropped from numbering in their millions to 40,000. The Murphy’s petrel succumbed to an apocalyptic passage of Murphy’s law. Their chicks figured high on the rodent menu, with a whopping 99% of them killed in their first week by rats.
Rats are neophobic, meaning they avoid new food. The good news is that the ship-borne helicopter effort went without a hitch. The poison seems to have worked, according to reports last month, with no rats sighted over an eleven-week period. Of course rats are resourceful, but rumours that they may have gone underground should prove fanciful. Elsewhere in the world, the apparently logical step of introducing cats to control rats often gave native islanders a second enemy to watch for.
On Puffin Island and the Calf of Mann, rats were cleared by poisoning. At 43km², Henderson is the largest tropical or subtropical island ever to see a rat eradication operation and third largest island treated in the world. It is also the first time aerial poisoning was carried out from the deck of a ship. The final denouement, as to whether the furry killers have been successfully terminated, will be known next year. If victory is achieved, expect similar rat operations elsewhere.
