By Daniel Cusick / Scientific American

If moose disappear from the boreal forest of northern Minnesota, as some biologists predict, they will not exit with a thunderous crash. Climate extinctions come quietly, even when they involve 1,000-pound herbivores.

Experts who have studied the Northwestern moose — Alces alces andersoni — believe they are witnessing one of the most precipitous nonhunting declines of a major species in the modern era, yet few outside Minnesota fully appreciate the loss.

The moose is an iconic species whose existence is woven into the social, economic and cultural fabric of this region. Its elongated head and wide antlers are emblazoned on everything from T-shirts to tire flaps. The 1960s cartoon character Bullwinkle J. Moose and his flying squirrel friend Rocky were residents of the fictionalized town of Frostbite Falls, Minn.

But the animals that inspired Bullwinkle are not what they were. Here, even healthy bulls — whose size, strength and rutting prowess make them the undisputed kings of the North Woods — are dying from what appear to be a combination of exhaustion, exposure, wasting disease triggered by parasites and other maladies.

The biologists are baffled and also helpless.

Mark Lenarz, who retired in March from the Minnesota Department of Natural Resources (DNR), where he led moose research efforts, said it’s not like the TV show “CSI: Crime Scene Investigation.”

“Unlike ‘CSI,’ it’s very hard to identify in the field exactly what an animal is dying from,” he said. “We know something about the symptoms” of distressed moose, he added, “but we don’t necessarily know the exact causes of mortality.”

What Lenarz and other experts do know is that a variety of climate stressors — including higher average annual temperatures, a long string of very mild winters, and increasingly favorable conditions for ticks, parasites and other invasive species — are conspiring to make northern Minnesota a moose graveyard.

Since 2002, Minnesota DNR specialists have put radio collars on 150 healthy adult moose; 119 subsequently died, most of them from unknown causes, according to wildlife officials. Car and train collisions accounted for 12 mortalities, while wolves were culpable in just 11 deaths.

Sudden collapse of herds

Meanwhile, annual surveys taken from helicopter overflights show that the state’s primary moose population, in the state’s northeastern Arrowhead region, has been halved in just six years, dropping from 8,840 animals in 2006 to just 4,230 this year. The decline mirrors a similar collapse a decade ago in the state’s northwest corner, where moose plummeted from an estimated 4,000 animals in the mid-1980s to less than 100 by the mid-2000s.

While some monitoring of moose had occurred in the 1990s, most of the animals were gone before scientists could examine cause-and-effect relationships. In the Arrowhead, however, experts are watching mass mortality, discovering multiple moose carcasses in the same area, including animals that appeared relatively healthy only a few years before.

It’s not just the occasional sickly moose succumbing to common causes of mortality, said Lenarz. “We’re out in the

field collecting dead radio-collared moose, and we were finding other moose that had died along with them.”

Similar mysterious deaths of one or more moose have been documented in Voyageurs National Park, where the National Park Service had launched its own radio-collar study of the animals, and in the Boundary Waters Canoe Area Wilderness, where moose sightings used to be routine for visitors but are increasingly rare.

Read more from Scientific American: http://www.scientificamerican.com/article.cfm?id=rapid-climate-changes-turn-north-woods-into-moose-graveyard