Rat Invasions Causing Seabird Decline Worldwide

Invasive rats on ocean islands are threatening the survival of many of the world's seabirds, according to a new report. The global analysis found that non-native rats have been observed preying on roughly a quarter of all seabird species, often with disastrous consequences. (See photos of rat-seabird conflict.)

The voracious rodents attack bird nesting colonies, eating eggs, chicks, and sometimes even adult birds.

Now 102 of 328 recognized seabird species are considered threatened or endangered by the World Conservation Union, with predation by invasive species ranking among the top dangers.

"Seabirds are important ecological actors in the oceans and on islands, but 30 percent of all seabirds are at risk of extinction," said study co-author Bernie Tershy of the University of California, Santa Cruz.

"Invasive rats are likely the single largest threat to seabirds," said Tershy, also a former grantee of the National Geographic Conservation Trust. (The National Geographic Society owns National Geographic News.)

Smaller seabird species and those that nest in burrows or rock crevices are particularly at risk, the study said.

That group includes storm-petrels, auklets, murrelets, and shearwaters, according to lead author Holly Jones of Yale University in New Haven, Connecticut.

"Rats can have a larger impact on entire seabird populations in species with adults that are small enough to prey on," Jones said.

"Burrow- and crevice-nesting seabirds share the same underground habitat [as rats], which makes a predation encounter more likely."

Oh, Rats!

Traveling with humans as ship stowaways, three rats species native to Europe and Asia have become established on about 90 percent of the world's major islands and island chains, experts say. In many cases the original invasions occurred centuries ago.

The Pacific rat first reached New Zealand, Hawaii, and many South Pacific islands on the canoes of early Polynesian voyagers, and Roman ships helped spread the black rat and brown rat throughout the Mediterranean.

Many seabird species considered vulnerable to rats have been showing local or global declines for decades and have now reached perilously low numbers, according to the researchers.

On rodent-infested islands, seabird breeding colonies often persist only on isolated rock outcrops that remain inaccessible to rats.

The researchers present their findings in the February edition of the journal Conservation Biology.

No Escape

Even some large species, such as the Laysan albatross, have proven vulnerable to the invaders.

"Because most seabirds evolved in the absence of any [land-based] predators, many have no evolutionary adaptation to avoid predation by rats," Yale University's Jones said.

The birds also have a hard time shifting their breeding locations to different islands to escape danger.

"Many seabirds are [genetically] programmed to return to breed where they were born," Jones noted.

Alan Saunders directs the Cooperative Islands Initiative at the University of Auckland in New Zealand. He was not part of the new study.

"No species is safe when rats arrive," Saunders said.

"Island ecosystems are especially vulnerable to induced change, and more extinctions have taken place on islands than anywhere else."

In addition to seabirds, he noted, invasive rats have caused extinctions of many native land birds, reptiles, frogs, and even plants.

"By consuming fruit, seeds, and flowers, rats can change the structure and composition of forests, and alter the entire ecology of islands."

Good Riddance to Rats

On Anacapa Island, part of California's Channel Islands National Park, breeding populations of the rare Xantus's murrelet and ashy storm-petrel had been decimated by black rats that were introduced prior to 1940.

But a successful restoration initiative between 2001 and 2002, which focused removing all non-native rodents using biodegradable poisons, has turned things around.

"Since rat eradication, [seabird] numbers seem to be increasing," Jones said.

(See a photo of Santa Cruz Island in the national park.)

Effective rat-removal techniques have also been pioneered in New Zealand, where more than a hundred previously infested islands are now rat-free.

While eradication projects such have been opposed by some animal rights activists, conservationists say rat removal is the only way some seabirds and other island species can survive.

"The eradication of invasive species from islands, especially rodents, has heralded a new era in conservation management globally," said the University of Auckland's Saunders.

"Spectacular ecological responses have been measured following rat eradications."

(Related news: "Canada Province Rat-Free for 50 Years" [March 31, 2003].)

Experts agree the new study should help conservation managers in different parts of the world prioritize islands for rat eradication and protect the seabird species most at risk.

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Doomsday Seed Bank Opens This Week

Arctic Vault Will Preserve Crops Threatened By Global Warming and Disasters Both Man-made and Natural

The Arctic doomsday seed vault will open this week, according to the Press Association.

The Svalbard Global Seed Vault is the world's insurance policy on a host of threats that could destroy important crops, from global warming and war to natural disasters like drought, flood and wildfire.

The vault's initial repository will include 250,000 varieties (10 million seeds) from "virtually every country in the world," according to the Association.

"All that can be seen of the vault outside the mountain is a concrete wedge, inside which a (410-foot) tunnel goes deep into the hillside, ending in three vaults with airlocked doors, keypad entry, stone and plastic-impregnated concrete walls," the Association reports. "The air has been cooled to between -18C and -20C, but Norwegian meteorologists have calculated that without power, the vaults would still be below freezing 200 years from now under the worst climate change scenario."

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Antarctic marine life threatened by crab invasion

Shell-crushing crabs cannot survive in cold water but rising temperatures will make Antarctic waters habitable

An army of shell-crushing crabs is poised to invade parts of the Antarctic Ocean that were off limits to the crustaceans for millions of years because of the intensely cold water.

Scientists believe that, as global warming causes sea temperatures in the region to rise, the unique shallow-water habitat of the Antarctic Peninsula will be transformed by the mass arrival of killer crabs.

Crabs are one of the top predators of the seabed but their enforced absence from the cold waters of the Antarctic has created an unusual community of shelled creatures that could disappear once the crabs invade, scientists said yesterday.

"The crabs are on the doorstep," said Sven Thatje of the National Oceanography Centre at Southampton University.

"Rapidly rising sea temperatures off the Antarctic Peninsula are creating conditions that favour the return of shell-crushing predators after an absence of tens of millions of years," Dr Thatje told the American Association for the Advancement of Science.

Sea-surface temperatures off the western Antarctic Peninsula have risen by 1C over the past 50 years, more than double the global average.

"Crab populations have already become established in deeper, slightly warmer waters. It is only a matter of time before they expand to shallow Antarctic habitats and radically alter community structure," he said.

Marine life on the Antarctic seabed is a rare combination of giant sea spiders, marine pillbugs and bottom-dwelling fish with antifreeze in their bloodstream to prevent them from freezing solid.

In the absence of crabs and other fast-moving predators, such as sharks and rays, the main seabed predators are slow-moving sea stars and giant, floppy ribbon worms. "Crabs cannot flush magnesium out of their blood, so when they are already moving slowly because of the cold, the magnesium makes them pass out and die," Dr Thatje said.

Clams, snails and other animals with hard skeletons have evolved into rare forms that are part of an unusual food web.

"Antarctic marine communities look like primeval communities from hundreds of millions of years ago because modern predators such as crabs and fish are missing," said Rich Aronson of the Dauphin Island Sea Laboratory in Alabama. An invasion of crabs could completely change the habitat, and "that would be a tragic loss for biodiversity in one of the last truly wild places on earth".

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