Nordic marauders loot Alaska's ecosystems

Invasive Norway rats infest many of the state's ports

Posted: Sunday, May 08, 2005

Joe Meehan was fighting rats at home before it became part of his job.

"I caught 45 rats in two weeks from under my house in Adak, using snap traps," Meehan said. "After that I started poisoning them, but the things started crawling up into the walls and dying. So I went back to trapping them."

Meehan worked as a wildlife biologist for six years in Adak, one of the many islands in the Aleutians infested by rodents during World War II military activity. Now based in Anchorage, he's working to develop an invasive rodent management plan for Alaska. Meehan works for the Alaska Department of Fish and Game, and he's particularly interested in protecting the Walrus Islands State Game Sanctuary.

"The plan will address how we can prevent them from being introduced or spread in the state, and how we can control or eradicate them," he said. "They aren't in Walrus Islands now, but we want to be sure if a few ever did get there we could respond before they reproduce and trash the islands."

Meehan's work is part of a growing effort to fight invasive rats in Alaska. Alaska's climate and relatively isolated location have made the state somewhat less susceptible to the rat infestations that plague many parts of the world, but state and federal biologists are concerned about the potential spread of rodents, in particular the Norway rat.

Stowaway rats colonized the Earth



Man is rats best friend.

Rats have long profited from their close association with humans, tagging along as people colonized the Earth. This commensal trait is just one of the qualities that have helped rats and mice spread throughout the world.

Almost any rodent can cause problems, but the commensal species are the ones you hear about, the ones that live around people, and most importantly around transportation, said biologist Peter Dunlevy, whose career has focused on invasive rodents. The problem starts when you move things from where they belong to where they dont belong. Rodents are good at exploiting this.

Three rodent species have caused the most profound problems worldwide: the Norway rat, the roof rat and the house mouse. All breed year-round, have short gestation periods and large litters. They quickly populate new environs and recover rapidly when their numbers are reduced.

Norway rats also known as cellar rats, sewer rats or wharf rats are the invasive rat seen most often in Alaska. Norway rats are not from Norway; they originated in temperate and northern regions of Asia and were spread worldwide on sailing ships.

Those common names are insightful. Norway rats thrive around water and are excellent swimmers. Tests have shown that Norway rats can swim for 50 to 72 hours in 35 degree water before exhaustion; they can dive and swim underwater for 30 seconds, and thus they can readily swim through the water seal of a toilet to enter a house.

Norway rats are considered semi-burrowing rodents and may develop extensive burrow systems, although they are quite at home in abandoned buildings, warehouses, barns, stables and open garbage dumps. They are gregarious and under favorable conditions colonies of several hundred rats may develop.

As invasive rodents, roof rats are the perfect complement to Norway rats. They are agile climbers and tend to live in branches or the crowns of palm trees, and are a major orchard and plantation pest. Also known as black rats and ship rats, they are the most common rat found on sailing vessels.

Roof rats originated in tropical and subtropical Asia, and are more widespread in tropical climates than Norway rats. At about 12 ounces, they are about 30 percent smaller than Norway rats. Good swimmers, they also possess the Norway rats outstanding ability to chew and gnaw.

The house mouse is more widely distributed worldwide than any rat species, living in tropical, temperate, steppe and semi-desert regions. With the exception of humans, they are the most widely distributed mammal on Earth.

Their original range included the Mediterranean region of Europe and Africa, stretching east through the steppe region of Asia to the East China Sea. Weighing just about an ounce, they are far smaller than rats but possess the same ability to spread disease, damage property and consume vast quantities of food. Because of their habit of nibbling and then discarding partially eaten food, they destroy more food than they consume. Like rats, they also foul stored food with waste.

All the problems rats do, mice do as well. Theyre just smaller versions and overlooked a little more, said Dunlevy.

As people spread across the globe, rodents took advantage of human transport, trade and colonization and tagged along. Rats and mice are responsible for billions of dollars of damage worldwide each year. They eat vast quantities of crops, food and livestock feed and contaminate far more stored food than they consume.

Rats' ever-growing, self-sharpening teeth chew through communication and electrical lines, and rats gnaw through soft concrete and aluminum siding, damaging buildings and structures. They also spread a variety of diseases to humans, livestock and wildlife.

Rats' profound impact on bird populations is well documented, and in the 1950s, invasive Norway rats devastated bird populations in the Queen Charlotte Islands just south of Ketchikan. But wildlife biologists in Alaska are concerned about more than birds - they're worried about the rodents' ability to restructure entire ecosystems.

"I've seen the damage rats can do all over the world," said biologist Peter Dunlevy. "Birds can be greatly impacted, but the primary issue is largescale ecosystem-level problems."

Rats are omnivorous. They eat eggs and birds, and they compete with native wildlife for seeds, plants and insects. Rats eat the seed bank and sprouting young plants, altering the entire vegetative community structure. Dunlevy said that's already happened in Hawaii.

"They are affecting the whole ecosystem from the bottom up," Dunlevy said. "You still affect birds when you change vegetative communities - a seed-eating bird is affected by seed-eating rats, even if they're not munching on your eggs or your babies. Insects are the second biggest category of food for rats, and that impacts insect-eating birds."

Dunlevy works for the Alaska Maritime National Wildlife Refuge, and was hired to design and implement a rat eradication program for the Aleutians. He came to Alaska three years ago after working on rat and other invasive species management programs in Hawaii and Guam.

About 17 large refuge islands in the Alaska Maritime National Wildlife Refuge have invasive rat populations from activities in World War II. Rats are established in some parts of Alaska: Ketchikan, Juneau, Fairbanks, Sitka, Nome and Kodiak, but Anchorage appears to be rat-free, and the Anchorage port is the only major world port to be considered rat-free.

Meehan said rat eradication programs are in their infancy in Alaska, but New Zealand has been dealing with rat infestations for years and has eradicated rats on some islands. Last year Dunlevy brought some of the best "ratters" from New Zealand to Alaska to contribute their expertise.

At this stage, Dunlevy, Meehan and others combating invasive rodents are assessing the risk of accidental introduction, surveying the extent of the invasion, evaluating potential eradication programs and establishing priorities.

"We're laying the groundwork, and testing methods that have been used elsewhere and that need to be fine-tuned for local conditions," Dunlevy said. "We're surveying areas to find precisely where rats are and what they're doing - what they're feeding on and what effects they're causing."

Protecting the rat-free and wildlife-rich Pribilof Islands is one priority. A rat introduction-prevention program is already in place there, with mechanisms to intercept stowaway rats. Rats are present on Kiska Island, and biologists are closely monitoring a large and productive auklet colony on the north side of island to gauge the impact.

"I've seen this colony and it's amazing, just swarms of birds," Meehan said.

Addressing the illegal importation and release of rats is another priority.

"We've had several incidents where it appears people have released pet rats," said Meehan. "Pet rats are illegal, unless they are albino white rats."

Meehan is optimistic about rat eradication in Alaska, especially in urban areas.

"We have the potential to turn this around," he said. "I can imagine we could eradicate rats from most communities where they exist at some point in the future."

•Riley Woodford is a writer with the Alaska Department of Fish & Game, Division of Wildlife Conservation. For more on Alaska's wildlife, see

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