Moose populations in Minnesota crashing as climate change deteroriates health

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May 20, 2012 |

Moose populations in Minnesota crashing as climate change deteroriates
health
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