Just two aging wolves survive on Isle Royale, the annual winter survey of wolves, moose and now beaver populations has confirmed.
The sightings announced last week were made in January and February and were not really a surprise. Although no actual wolves had been seen a year earlier, the tracks of two wolves were abundant during the previous survey, and at times indicated that the aging pair was healthy enough to engage in “side-by-side cavorting.”
Nor does their persistence through another year, in perpetually difficult conditions and without the support of a surrounding pack, change their dimming outlook or the policy decisions that will be made over the next six months or so.
But the new observations add some dispiriting detail to the picture of this iconic species fading slowly to black in a place that was once among its leading refuges.
The two survivors, a 9-year-old male and 7-year-old female, were seen with sufficient clarity this year to establish that they still have their canine teeth, according to Rolf Peterson, the longest-serving researcher in the Isle Royale project. A wolf without canine teeth is profoundly handicapped in taking down the moose that are its principal food source on the island.
Still, the researchers saw only three moose kills that appeared to have been made during the 46-day period of the aerial observations, from January 18 to March 4.
In addition, the wolves were seen early on to be feeding on a calf they had killed before the study period, and later to be scavenging the remains of an adult moose that had probably died of starvation rather than predatory attack:
The moose had been an old bull with necrotic teeth. The percent fat content of its bone marrow was 12% (normal is > 70%) — indicating that it was in a state of severe nutritional depletion at the time of its death … the carcass was buried in snow and the sternum had not been consumed.
As for the possibility of reproduction, that question has been more or less answered, and in the negative.
Ineffable familial relationship
The survivors are a remnant of the Chippewa Harbor pack, siblings who share a mother; in addition, the female is the daughter of the male, creating a relationship permutation that Peterson told me last year is one we don’t even have a word for.
On February 27th, the two wolves were observed again near their kill on Tobin Creek. This time the female was obviously in estrus and the male courted her incessantly, but to no avail. The female responded to the courtship advances of her father with intense aggression, perhaps an example of incest avoidance behavior that is generally present among animal species.
And just as well, probably. Their last offspring, a pup born in 2014, was seen from the air during the 2014-15 winter survey, at about 9 months of age, displaying a stunted tail and probable spinal deformity that indicated a short life span. By last winter’s survey this wolf, too, had disappeared.
The Chippewa Harbor Pack has not produced any viable pups since the alpha male died, along with two pack mates, in a historic mine shaft in December 2011. Under present circumstances reproduction is not expected.
And completes a cycle that began with the wolves’ arrival on Isle Royale in the late 1940s, continued through the formation of three packs with combined membership typically in range of 18 to 27 animals, then reversed in 2009.
Since then the population has fallen from 24 to the surviving pair, a consequence of many factors with the “genetic depression” of decades-long inbreeding in the lead position.
Park service’s timetable
By this fall the National Park Service hopes to reach a final decision on what to do about replacing the wolves, having signaled last December that its preferred approach was to try to maintain the island’s modern-day ecosystem by locating and importing new mainland wolves in a program whose details remain unsettled. It’s possible, though far from certain, that a new wolf population could be in place by the end of 2018.
In an announcement of this year’s study issued by Michigan Technological University, its academic home, Peterson said:
If you took wolves from different groups, you might want to space them as much as you could away from each other, just because they’re all trying to figure out the new landscape and establish territory, and you know, they won’t all get along necessarily. But there’s a limit to how much you can manage that sort of thing. You know, the wolves have to figure a lot of that out on their own.
In the meantime, the long-predicted impacts of wolf’ loss continue apace.
Since predation essentially ceased six years ago, the moose population has been growing by more than 20 percent per year and is estimated in the new survey at 1,600 animals, despite thawing/refreezing patterns that crusted the snow and made counting difficult until mid-February, when fresh powder “greatly improved counting conditions to what could be described as slightly worse than average.”
The moose are now a predominantly youthful population, too, which suggests that “if recent growth rates persist for the next 3-4 years, the population will double in size.”
That is bad news for the balsam fir forest in particular, which had been recovering to its healthiest state in a century or more until the wolves went into their current decline.
… Recent evidence [is] that stunted balsam ﬁr stems, browsed for decades and less than one meter tall, had started to grow in the past decade prior to 2012 when the moose population began to increase rapidly. These short ﬁr trees, some established as seedlings as long as 40-50 years ago, now represent the ﬁnal cohort of short ﬁr that could grow into seed-bearing trees of the future. This is the species’ last chance because the parent trees are reaching maximum life-spans and most have died and fallen over in the past 25 years.
As for beavers, a secondary food source for wolves, this year’s study found that the “population has continued to increase, a pattern initiated when the wolf population collapsed in 2010-2012. There were almost 300 active beaver sites in 2016, a three-fold increase in the past half decade.”
The report does not discuss the implications of the beaver surge in much depth, but anybody who spends much time at the intersection of woods and water can appreciate their capacity for reshaping landscape — especially, perhaps, in an isolated island system that confines them as effectively as it long excluded wolves.
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The full report from the Isle Royale annual winter survey for 2016-2017 can be read here.