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Jun 12, 2009 03:25 PM | 11
Last year, one of the world’s most aggressive island restoration projects was launched to poison all the invasive rats on Alaska’s Rat Island, located in the western part of the Aleutian islands. But the extermination project may have taken an unexpected toll: a recent survey of the island recovered the corpses of 41 bald eagles and 186 glaucous-winged gulls – raising the possibility that the birds died after consuming poisoned rats.
“When you go to an island after a winter, it's not surprising to find bird carcasses,” says U.S. Fish and Wildlife spokesman Bruce Woods, “but not these numbers.” There were only four breeding pairs of the federally protected bald eagles residing on the island last year, but the population in the Aleutians numbers 2,500.
Norway rats—the global pest of subways and sewers—first arrived on the island known to the Aleut people as Hawadax in 1780. A rodent-infested Japanese sailing ship ran aground and rats spilled onto its rocky shores, devastating populations of ground-nesting seabirds by feeding on their eggs, chicks, and even adults. When Captain Fyodor Petrovich Litke visited the island in 1827, he named it Kryssei, which means rat in Russian. The rats have kept bird numbers low ever since.
In 2006, the U.S. Fish and Wildlife Service, the Nature Conservancy and Island Conservation began testing out rat eradication strategies in small areas in other parts of the Aleutians using cakes of grain laced with a rodent-killing blood thinner called brodifacoum. During the trial, 88 percent of rodents perished in their burrows where they would not be exposed to scavengers like eagles or gulls, according to an environmental assessment of the project. Scientists concluded that “some bald eagles may be exposed to brodifacoum residues but are unlikely to die.”
On April 15, 2008, the Rat Island Restoration Project got the formal go-ahead, and in September a helicopter hovered over the 10 square mile island dropping the poisoned grain in a grid pattern. “The idea is to put every rat in jeopardy, to spread the bait in sufficient density so that every rat will consume a lethal dose,” the Nature Conservancy’s Steve MacLean told American Way magazine at the time.
Immediately after the poisoning, wildlife workers scoured the ground and found only a dozen rodent carcasses. “There were not a lot of piles of rodent bones or rodent fur that would be expected if a lot of rats had been consumed on the surface,” Woods says. If scavenging indeed was minimal, then something else killed the eagles and gulls.
In any case, the recent tragedy represents a blow to a powerful restoration strategy that has already pitted conservationists against landowners and animal rights activists in New Zealand, California, and Hawaii. The corpses were sent to the National Wildlife Health Center’s laboratory in Madison, Wisc., and a determination on the cause of death should be available in late June. At least 75 percent of the carcasses were juveniles.
The good news is that the survey team reports that Aleutian cackling geese, ptarmigan, peregrine falcons and black oystercatchers are all nesting on the island -- and rats appear to be absent. “If the rats are truly gone,” Woods says, “then the long-term benefits to the ecoystem will outweigh the loss of these birds.”
Image of bald eagle courtesy Alex Layzell via Flickr.
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11 Comments
Add CommentThe eagle population will recover. If the action managed to wipe out the rats, it will be well worth it.
Reply | Report Abuse | Link to thisIt is better to avoid killing large numbers of the wrong animals, but we have to look at the total environment perspective. Lately, we have moved into an individual animal's rights mode. This is very bad for environmental management. Populations and environments matter. Individual animals do not.
Best laided played plan's of mice and men.To bad about the eagles.
Reply | Report Abuse | Link to thisSome years ago I was standing in line in a huge grocery-store pharmacy, waiting patiently to get my prescription of coumadin refilled. To my amazement a large white rat crawled out of the coat pocket of the woman standing in line directly in front of me, scrambled up her chest and took up a perch on her right shoulder, playfully nosing her ear.
Reply | Report Abuse | Link to thisThis apparently was a pet rat. Still, I was grossed out at the thought of it in a grocery store and just for a minute the devil made me wish my coumadin bottle was filled already. All it would take is one little white pill slipped into the woman's coat pocket and Mr. Rat would be history. Rats really don't like having their blood thinned.
to bad about the eagels what in the hell is the matter with you!
Reply | Report Abuse | Link to thisI hope SciAm follows up this story with a report on the autopsy.
Reply | Report Abuse | Link to thisI'll bet the eagles and gulls starved to death due to the lack of rats and were not poisoned. Believe it or not gulls are better rodent hunters then eagles.
Reply | Report Abuse | Link to thisBit of an overkill! All rodenticides blanket kill every animal in the area so of course the poison killed the eagles (through secondary comsumption) there will also be hundreds of other "non-target" birds and animals which died through consuming the poisoned grain. . The area will also be contaminated for a very long time! Some rats will doubtlesss have survived and now with out any competition or preditors in the way the next population will explode! Biocides are a con, ban them!
Reply | Report Abuse | Link to thisThe rodenticide used in this case turns into harmelss compounds when it is exposed to the elements. It has not contaminated the area. These areas of Alaska have very healthy sea bird and eagle populations and the loss of these birds will be a blip on the radar to the overall recovery of this island, IF the rats are truly gone.
Reply | Report Abuse | Link to thisThis story was recently covered by Public Radio. The tone of the interviewer was incriminatory when interviewing an Alaska wildlife official. The unfortunate loss of predatory birds may just have been a speeding up of restoring a natural balance that would have occurred anyways. The predatory bird population was most likely elevated because of the abundant rat food source and would decline naturally with it removed. Also the laudable objective was to restore a natural habitat for many other bird species and this is working well. The candle is thus indeed worth the flame and good job Alaskan Wildlife.
Reply | Report Abuse | Link to thisPlease tell me, "why" no one thought of the food-chain when poison is used? Bald Eagles are hunters but also scavengers and for all these Conservation groups to allow this, just boggles my mind.
Reply | Report Abuse | Link to thisI don't poison mice, due to my Blue Jays and other birds would then be poisoned after eating the dead mice...what in the hell did they think would happen to the dead rats?
My donation dollars will be going elsewhere from now on...this is a very sad day!
Betcha the rodent poison used in this instance was a blood-thinner and did not harm the birds or anything else other than maybe mice, if there were any on the island not eaten by the rats. It is true, however, that rats are gradually evolving to be more tolerant of the poisons which work so specificially well against them. Still, it will be a long time before the micro dose that presently kills rats has to be increased enough to harm most other things.
Reply | Report Abuse | Link to thisNever underestimate the chance that the birds were killed not by the poison, but by some fluke carrion bacteria that flared up because there were so many rat carcasses all at once. Every animal on this planet bigger than a mustard seed is constantly at risk from living organisms much smaller that generally we live in a kind of symbiosis with or at least a stalemate. It could be that something really indirectly related to the rat population was perturbed just enough by the rat extermination that it caused a common bacteria to change just enough the overwhelm the immune systems of the birds.