Rolf Peterson and John Vucetich
Rolf Peterson and John Vucetich
Isle Royale Moose
Isle Royale Moose
John Vucetich tracks a moose that is infested with ticks.
John Vucetich tracks a moose that is infested with ticks.
Wolves Research
Severe winters in the late 1960's usher in a decade of moose decline and wolf increase.
Moose on Ice
Moose crossing a frozen pond
“When the population is large, nutrition is poorer.”

For more information on wolf-moose research:

Wolves, Moose, and Michigan Tech

by Jennifer Donovan

Wildlife ecologists Rolf Peterson and John Vucetich keep an eye on the wolf-moose relationship.

The ranks of the wolves and moose of Isle Royale may be thinning, but as the study enters its fiftieth year, the predator-prey research is going strong.

Wildlife ecologists Rolf Peterson and John Vucetich, from Michigan Tech’s School of Forest Resources and Environmental Science, and graduate student, Joseph Bump, have compiled data for four new research studies and are preparing papers for scientific journals during the Isle Royale wolf-moose study’s golden anniversary year.

The studies examine

  • how arthritis in moose is linked to prenatal nutrition,
  • how wolves affect the evolution of the size of moose,
  • how wolves cause plants to grow bigger, and
  • how moose teeth reveal the effectiveness of legislation designed to lower mercury levels.

Moose get the same kind of arthritis that affects humans as they age, and it is common in the moose of Isle Royale. Peterson has been examining moose bones found on the island over the past thirty years. He found that evidence of the incidence of arthritis follows clear cycles, rising or dropping dramatically depending on the size of the herd and the availability of nutritious food.

“When the population is large, nutrition is poorer,” the researcher explains.

After decades of research, Peterson also has been able to link arthritis in aging moose to poor nutrition: both prenatal and immediately after birth. He can determine the age of an arthritic moose bone and then, knowing that the herd was large and the winter harsh in any given year, he can compare nutrition and arthritis rates.

Vucetich has been collecting evidence that predators affect the body size of their prey. Wolves favor smaller moose, he explains, so the moose that survive to reproduce tend to be larger animals. Vucetich has compiled what is likely the first documented evidence of this phenomenon in the wild.

Bump’s research examines the interconnection between wolves, moose, and the plants that grow on Isle Royale. By hunting moose, whose carcasses are tremendous sources of nitrogen and phosphorus, wolves alter the amounts and distribution of those chemicals in the soil. When the ground is rich in nitrogen and phosphorus, plants grow bigger and are more nutritious, making them more attractive to moose.

In other research, Peterson and Vucetich have been able to demonstrate the effectiveness of the Clean Air and Water Acts of 1970 in lowering the levels of mercury in the air and water. Mercury gets deposited from the air on plants, Peterson explains. Plant-eating animals such as moose eat the mercury-laden vegetation, and, as their mercury levels rise, the chemical is deposited permanently in their teeth.

John Vucetich tracks a moose that is infested with ticks.

Vucetich and Peterson have been looking at mercury concentrations in the teeth of moose calves during their first year of life. “We study calves during their first year, because then we knew that any mercury found was deposited that year,” the scientist explains. Canadian and Norwegian colleagues Peter Outridge, Rune Eide, and Rolf Isrenn contributed critical lab work.

Soon after the Clean Air and Water Acts were passed, the mercury levels had dropped by two-thirds, Peterson reports. Other researchers have found similar effects in small studies in limited locales, but the Isle Royale study is the first one that spans an entire ecosystem.

Scientists have been studying the interactions of wolves and moose at Isle Royale National Park for half a century. In the late 1940s, a pack of wolves made the trek across fifteen to twenty miles of frozen waters of Lake Superior from Canada to Isle Royale. There they found a wilderness island safe from hunters and traffic and home to an abundant moose population. The wolves settled in to a self-contained ecosystem where they were virtually the only predators and the moose were their primary prey.

Conditions on the island made an ideal laboratory for scientific study of the predator-prey relationship free from outside influences. In 1958, biologist Durward Allen launched the Isle Royale wolf-moose study, chronicling population fluctuations of both kinds of animals and observing wolf-moose interaction and environmental changes to help explain these fluctuations.
The study continues today under the leadership of Peterson and Vucetich. They do aerial and ground observations in summer and winter, collect moose and wolf bones to analyze, and study vegetation, climate, air and water contaminants, and other environmental factors.

“Although wolves and moose are in the spotlight, this study has implications for understanding the broader components of an ecosystem,” says Peterson. The primary lesson learned from this long-running study is that wildlife systems are complex, unpredictable, and dynamic by nature, and they are influenced by a large number of environmental factors, added Vucetich.

“The data collected in the Isle Royale study provide a historical perspective that is very different from isolated snapshots of five- or ten-year periods,” he explains.