The Ecosystem Engineer: Research Looks at Beavers' Role in River Restoration.

Beavers are often called ecosystem engineers because they can radically alter stream or valley bottom ecosystems, said Melinda Daniels, an associate professor of geography who recently studied the connection between beavers and river restoration. Beaver dams create diverse river landscapes, she said, and can turn a single-thread channel stream into a meadow, pond or multichannel, free-flowing stream.

"Our argument is that the restoration target for streams with forested riparian zones has got to acknowledge the diversity brought to river systems by active beaver populations," Daniels said.
Daniels and three researchers from the University of Connecticut co-authored

"The River Discontinuum: Applying Beaver Modifications to Baseline Conditions for Restoration of Forested Headwaters." The article, led by Denise Burchsted at the University of Connecticut, appears in a recent issue of BioScience, the journal of the American Institute of Biological Sciences.
While the research involves observations of several watersheds in northeastern Connecticut, the results are applicable to any forested stream, which typically have large beaver populations. Beaver populations have rebounded in recent years, Daniels said, after coming close to extinction in the early 19th century by hunters for their fur.

The ultimate goal of the research, Daniels said, is to help restore rivers in an efficient way that acknowledges ecosystem diversity and doesn't destroy it.
"A lot of rivers are in trouble and need work and restoration, but it's amazing how little we know about the systems we're trying to fix," she said. "We know they're broken, but we don't exactly know what they should look like because we know so little about how many of our river systems function."

Current restoration projects often don't consider the role of beavers as ecosystem engineers, and instead focus on creating continuous free-flowing streams, Daniels said. Such restoration can be expensive because it usually involves completely tearing down small 19th-century milldams and re-engineering an entire valley bottom.

Rather than tear down the whole milldam and radically change the surrounding ecosystem, the researchers recommend river restorers only remove part of it. This allows some ponded water to remain and mimics the role of beavers. Daniels said that in many cases if an old dam breaks and forms a gap, beavers may build their own dam to patch the gap and recreate the ecosystem that previously existed.

The researchers plan to continue river observations and collect more data to provide river restorers with insight for maintaining river ecosystem diversity.
"You can use these natural analogs to produce an ecosystem that looks a lot more like the one that was there before the colonists arrived," Daniels said. "We can restore rivers in a way that mimics the naturally diverse beaver streams, and we can save a lot of money in the process."

Beaver, cutting down a large oak tree. When engineers restore rivers, one Kansas State University professor hopes they'll keep a smaller engineer in mind: the North American beaver. (Credit: iStockphoto/Steve Greer)

Mariana Crow Will Go Extinct in 75 Years, Study Suggests

Researchers from the University of Washington say the Mariana crow, a forest crow living on Rota Island in the western Pacific Ocean, will go extinct in 75 years.

The extinction could happen almost twice as soon as previously believed.

The crow's extinction can be prevented with a bird management program that focuses on helping fledgling birds reach their first birthday, said James Ha, UW research associate professor in psychology.

Ha examined survival rates in 97 Mariana crows -- Corvus kubaryi -- that had been tracked between 1990 and 2010 by researchers. He found that 40 percent of fledgling crows made it to their first birthday.
The rapid decline of young birds is twice what researchers previously estimated.

"It's the first year of survival that's the most crucial," said Ha, lead author of a report on the research. "If only 40 percent of fledglings survive their first year, then we predict the species will go extinct in 75 years."

Ha and his co-authors published the report in the current issue of Bird Conservation International.

The 75-year extinction estimate is according to a population model that factors in the estimated number of existing Mariana crows -- 330 -- with the 40 percent first-year survival rate, average number of fledglings per nest and fertility of female birds. Using this model, Ha found that 91 birds would exist in 20 years and that in 75 years the species would be extinct.

Previously, biologists believed that the first-year survival rate of Mariana crows was higher, around 60 to 80 percent.

When Ha used those estimates in his population model, the outlook was not as grim for the birds. At 60 percent first-year survival rate, Mariana crows would dwindle to 218 birds in 20 years and become extinct in 133 years. And an 80 percent first-year survival rate projects that in 20 years there would be 453 birds, a growing population that would avoid extinction.

"According to the population model, if we can boost fledgling survival from 40 percent to 70 percent, the Mariana crows will be fine," Ha said.
Of the about 35 crow species, Mariana crows are considered rare and classified as critically endangered. Weighing about a half of a pound, Mariana crows are 40 percent smaller than other crows, such as the Northwest crow.

Monogamously-mating, Mariana crows live exclusively on Rota Island, populated by about 1,200 people and located 56 miles northeast of Guam. Rota is a U.S. territory and is up for consideration as a U.S. national park.
Ha and Renee Ha, co-author of the report and UW research scientist in psychology, fear that Rota faces the same avian demise as Guam, which has no
forest birds.

Brown tree snakes introduced to the island after World War II wiped out native birds, such as the Guam flycatcher and the Rufous fantail.
The Has suspect that the uncontrolled increase of feral cats on Rota is leading to the decrease of Mariana crows, much like brown tree snakes led to the disappearance of forest birds on Guam.

The researchers say that a captive rearing program could save the Mariana crows. They hope to set up a rearing facility where they could incubate eggs from the wild, raise the fledglings until their first birthday and then release the grown birds into nesting sites on the island.

The study was funded by the Commonwealth of the Northern Mariana Islands and the U.S. Fish and Wildlife Service. Co-author Alyssa Butler graduated from UW with a bachelor's degree in biology and is now a staff member at the Pali Institute, a science education camp in California.

This is a fledgling Mariana crow. (Credit: Sarah Faegre)