In yet another effort to untangle the mystery behind Minnesota's diminished moose population, renowned wolf researcher David Mech is reporting a stark correlation between wolf population levels and survival of moose calves.
Mech was the lead author of a research paper published online this month in the journal Wildlife Society Bulletin that found rapidly increasing wolf numbers in Northeastern Minnesota from 2001 to 2009 coincided with the rapid demise of moose in the region - from nearly 9,000 moose in 2006 to fewer than 4,000 in recent winters.
Mech, who has been studying wolves in an 800-square-mile area of the Superior National Forest for decades, said wolf numbers more than doubled while moose declined, from fewer than 50 wolves in the study area in 2001 to nearly 100 by 2010.
The number of moose calves surviving to their first winter peaked at 0.93 per cow when wolf numbers were lower but dropped as low as 0.24 when wolf numbers peaked, the study notes. That level is considered unsustainable for moose to continue a thriving population, especially with so many adult moose dying from other causes.
But the trend may be reversing.
A recent stabilization of the Minnesota moose herd, and a slight increase in calf survival seen in the last few winter surveys, also coincides with a sharp decline in wolf numbers in the study area, the study found, showing the correlation works in reverse, too.
The study cites a previously unreported decline in wolves in the heart of the national forest in recent years - down to 34 or fewer wolves in the study area in 2017, less than half of the 82 wolves estimated in 2012.
Moose calf survival increased some as wolf numbers dropped, from the 0.24 low in 2011 to 0.36 per cow last year.
"We do not claim that wolf numbers only influence moose population during declines nor that wolves are the only factor affecting moose numbers," the study concludes.
Recent wolf and moose population data only show "suggestive information" on the plight of moose, the study noted. "However, our new and revised data signal a critical downward trend in the wolf population in our study area and an apparent response by moose."
Wolves in the study area declined due to fewer moose to eat, the study notes, but also because of hunting and trapping allowed in 2012, 2013 and 2014 when wolves were briefly off the federal protected list.
The study stops short of saying wolves were the primary cause of the overall moose decline.
"Would the Northeastern Minnesota moose population be declining if there were no wolves? Our findings do not answer this question definitively," the report notes. But the findings "suggest that the decline of Northeastern Minnesota moose since 2006 at least would not have been as steep without wolves' presence and influence."
Mech and co-authors John Frieberg and Shannon Barber-Meyer also go back to show similar relationships in past decades, noting a brief but dramatic moose decline in the early 1990s corresponded with a rapid rise in wolves at the same time.
The new study doesn't refute any of a number of other research efforts looking to solve the moose mystery. Recent Minnesota Department of Natural Resources research shows wolves are clearly a factor in moose deaths, along with parasites such as winter ticks and a brainworm spread by deer. Bears also kill a significant number of newborn moose calves each spring.
Other researchers note that a long-term trend to warmer and less snowy winters has helped push deer numbers up in the moose range of Minnesota, spreading more brainworm north. That warming trend also has lead to a higher survival rate of ticks. And scientists say warmer weather leads to more moose stress, causing moose to eat less and store less fat to survive winter.
Other researchers note that habitat for moose has declined in many areas making it harder for them to thrive. Moose like second-generation forests, such as those that followed recent large fires in the region, some of the few areas where moose numbers have actually gone up in recent years.
State and tribal wildlife officials currently are conducting aerial surveys of moose in selected area of Northeastern Minnesota and will release their updated annual population estimate later this winter.