A rodent-control programme killed 46 bald eagles and hundreds of other birds

Flaws in Alaskan island rat-eradication project laid bare.

A rodent-control programme on remote Rat Island in the Aleutian archipelago killed 46 bald eagles and hundreds of other birds.

Misjudgements made two years ago during a rat-eradication programme on Alaska's aptly named Rat Island, which led to the death of more than 420 birds — including 46 bald eagles — have now been detailed.

A report by the Ornithological Council — an association of ornithology organizations in the Americas — documents flaws in the eradication programme carried out by the US Fish and Wildlife Service (FWS) and two conservation groups on the remote Aleutian island, which lies within the Alaska Maritime National Wildlife Refuge. The key finding is that Island Conservation, the group based in Santa Cruz, California, that led the operation, applied poison in excess of that recommended by an advisory panel and probably above the legal limit approved by the US Environmental Protection Agency (EPA).

"Rat Island was a huge and complicated project," says Steve Delehanty, manager of the Alaska Maritime National Wildlife Refuge. "It was a learning experience, and we made mistakes together."

Rat Island earned its name some time after 1780, when a Japanese sailing ship was wrecked near the coast and spilled its four-legged castaways into the water. The invasive rats fed on the eggs, chicks and adults of ground-nesting seabirds, such as Aleutian cackling geese and black oystercatchers, rapidly devastating the native bird populations.

By September 2005, a collaborative restoration effort had begun to gain steam with funds from the US Nature Conservancy along with public funding, and Island Conservation tested grain cakes to be laced with the anticoagulant rat poison brodifacoum on nearby islands.

In November 2007, Island Conservation asked the Island Eradication Advisory Group, based in New Zealand, to review the possible baiting strategies that it had developed. The advisory group characterized Island Conservation's proposed poison applications as "prodigious", noting that on New Zealand's Campbell Island, which was said to have had the highest density of rats in the world, only 6 kilograms per hectare of brodifacoum-laced bait was used on flat terrain.

Island Conservation, however, decided to apply 12 kg ha-1 of the bait on coastal areas during its first application and 6 kg ha-1 during a follow-up several days later. The Ornithological Council report, commissioned by the organizations involved in the eradication programme and led by pest-control expert Terrell Salmon, recently retired from the University of California, Davis, noted that the reviewers "found no documentation explaining this decision".
Poison by the tonne

As the operational plan was getting approved, the US Department of Agriculture prepared a project-specific pesticide label — a legally binding document that sets down application methods and limits — and submitted it to the EPA. In addition to the 36 tonnes of bait that Island Conservation planned to bring, the project would ship an extra 10 tonnes of 'contingency' bait in case of problems.

Although the approved operational plan set aside funds for disposal of any excess bait, Island Conservation's project manager Stacey Buckelew told the Ornithological Council that "there was no plan to return excess bait to the manufacturer or to dispose of it". Buckelew, who now works for Alaska Department of Fish & Game in Anchorage, did not respond to requests for comment from Nature.

In September 2008, helicopters and ground-based workers dumped all 46 tonnes of bait on the island's 2,800 hectares over the course of a week.

The first application on the coast was largely under the legal limit of 18 kg ha-1 set down on the pesticide label. However, the second application, which effectively included all of the contingency bait, was estimated to be between 17 and 22 kg ha-1, around twice the label limit of 9 kg ha-1 for this application and three times the target rate, according to the report. Eight months later, biologists returned to the island and discovered the bird carcasses, which were found to contain traces of the poison.
Nontarget mortality

Island Conservation told the Ornithological Council they were using "nominal rates" averaged over parts of the island because of uncertainty in the work and the need to ensure there were no gaps in coverage. Gregg Howald, Island Conservation's North America Regional Director, declined to respond to specific questions from Nature, but provided a statement that the group will use the report to "minimize the risk of nontarget mortality" in future eradication efforts.

The FWS asked the Ornithological Council to make a determination on whether the bait drops violated the label, but the council declined to do so, stating that it would leave the "legal question" to "those who are charged with that responsibility". Separately, Rory Stark of the FWS law enforcement office in Anchorage investigated the bird deaths as required under the Migratory Bird Treaty Act and the Eagle Act, and the investigation is ongoing.

The conservationists might have been more fastidious about the amount of poison used if they had not been operating on false assumptions about bird biology. A few birds, including eagles, were expected to die from the operation, but not nearly as many. The initial environmental assessment suggested that bald eagles would leave Rat Island in September for the salmon run. However, when glaucous-winged gulls began nibbling on poison baits and dying en masse, their carcasses attracted the eagles, who succumbed to secondary poisoning.

Today, Rat Island is rat-free, and an application for a new name is pending. Delehanty says the FWS will continue to eradicate non-native mammals that cause ecological problems in the Aleutians and will work with Island Conservation in the future. "In the long run, we've provided habitat for tens of thousands of birds," he says, "I don't like to see a single one harmed, but if you do the math this was a rip-roaring conservation success."

Brendan Borrell
Published online 18 January 2011 | NatureNews

http://www.nature.com/news/2011/110118/full/news.2011.24.html?s=news_rss