Happy Wolverine Birthday 2018!

February 14th is the symbolic birthday of wolverines around the world. Here’s a little card that goes out to wolverine kits and wolverine supporters everywhere, with lots of love to all.

Wolverine Birthday 2013

It’s February 14th once again, which, as everyone knows – or should know – is a very important day: Wolverine Birthday. This is the approximate date of birth for wolverines all over the world. Mid-February marks the descent of pregnant female wolverines into their snow dens, there to give birth and attempt to raise their kits, moving them uphill through a series of maternal dens until they are big enough to emerge. This happens sometime in late spring, usually mid-May, after which the kits hang out in their parents’ territories, sometimes alone, sometimes following their mother, sometimes their father, until they set out to find a territory of their own, about a year after they’re born.

A photoshop sketch of a wolverine mom and kits in their snow den, made several years ago and scrapped because it was way too cute, and the kits look weird (also, these guys are a few weeks old, not newborns.) But whatever. Happy Wolverine Birthday.

A photoshop sketch of a wolverine mom and kits in their snow den, made several years ago and scrapped because it was way too cute, and the kits look weird (also, these guys are a few weeks old, not newborns.) But whatever. Happy Wolverine Birthday.

At least, this is the basic outline of the first year of a kit’s life. Bob Inman and Audrey Magoun published a paper in 2012 reviewing all recorded wolverine births, as well as information obtained from trapped carcasses of pregnant or lactating females, and the birth dates generally ranged from late January through mid-March, with reports from the 1950’s of wolverines giving birth as late as April. So the February 14th date is a handy mnemonic device that doesn’t necessarily reflect an absolute reality. The lack of an absolute reality is interesting, as are the reports of much later births earlier in the century and further to the north. Wolverines mate in the summer, but the fertilized embryos don’t implant until later. The exact triggers for implantation (the technical term is nidation) remain unclear, but probably have to do with the female’s body condition – without a certain level of fitness on the part of the female, the embryos will simply dissolve without ever implanting. The range of birth dates means that there is also a range of nidation dates, which could be solely dictated by the percent body fat of the female – or could also be triggered in part by environmental factors. Maybe, then, there’s some range of potential adaptation to changing climate conditions? This is speculative, of course, but if it turns out to be true, it’ll make my valentine’s day every year for the rest of my life.

All of this just complicates my agenda to turn an otherwise annoying holiday into something with real meaning, however. So for now, let’s just stick with February 14th, and I hope everyone out there is having a great Wolverine Birthday. More posts soon!


First Captive Kits in the UK

Three captive kits born in January have emerged from their den and are now on public view in the Cotswold Wildlife Park in Oxfordshire, England. BBC has posted a video of the kits, which are the first ever born in captivity in the UK. The Oxford Times also ran a story about the event. The kits and their parents are part of a European captive breeding program for endangered species, and the kits will eventually move to new homes as part of this program.

The kits were in the den for nine weeks, which is slightly less time than we generally allow wild wolverines, although there is some debate on this. Right now we use February 14th as the default birthday for wild wolverine kits, although this probably ranges from January through March, depending on the female and local conditions. We use May 15th as the benchmark date at which kits are out of the den – and, by extension, the last date at which snow must remain on the ground in order for a region to support a breeding wolverine population. These dates allow a full 12 weeks in the den. Some wolverine researchers believe that the May 15th date might be later than necessary, however, and propose a late-April cutoff for den emergence and snowmelt.

The BBC piece mentions that the female has kept her mate away from the den and the kits. Traditional lore and early research in Scandinavia suggested that males entered dens to kill kits, although later research suggested that infanticide was probably the result of interloping males killing unrelated babies. The Glacier National Park project showed that fathers visited their kits and might even help raise and teach them, and in the Absarokas, our male M57 was observed in close proximity to F3’s den last year. We now know that F3 had at least one baby in 2011, a male, so this may be further evidence that M57 played some role in raising the family. On the other hand, the dynamics of wolverine social interactions remain murky, and there may be more to the story than we are aware.

In any case, the birth of these three captive kits is a big event for the UK – perhaps even the first wolverine births there since the Pleistocene. If you’re lucky enough to be in the area, drop by the zoo and say hello to them, and be sure to take some pictures and share them here.



Where Wolverines Are Born

When I set out last week with the coordinates for F3’s den programmed into my GPS and the site marked on a series of paper maps, I couldn’t shake a feeling that approached sheer giddiness. The opportunity to examine a wolverine den site is akin to winning some kind of wildlife biology lottery; the dens are as inherently rare as the species, and the dens that are known to science are even fewer. Only around 15 have been documented in the Lower 48, leaving a huge gap in our knowledge of reproductive dynamics. For years, F3 had failed to den, and the instruments on our other female, F133, had died, so we had no way of knowing whether she had had kits. When F3 evidently did den this year, I was ecstatic, but I was also in Cambodia. I was starting to think that I would never have a chance to investigate a den site. When I made it back to the Rockies earlier than expected, in August, getting to F3’s den site was one of my priorities.

A crew visited the den in May, when the snow was still on the ground, and some of the same crew members had gone back once the snow melted, in July, to investigate the site and to see if they could find scat samples. The spring crew hadn’t seen the kits or verified their existence, so however strong the circumstantial evidence, we couldn’t be certain that the site was a den instead of a food cache, and we couldn’t say with confidence that F3 and M57 had reproduced. The July crew had looked for latrine sites, which are proof that a site was used as a den. And the crew found them in abundance, pulling out a number of scat samples for analysis. They hadn’t gone digging for the kits or attempted to instrument the babies in May because of funding constraints, so the scat samples, in addition to confirming that this was a den site, also offered a chance to identify new individuals and perhaps determine their sex.

The important work had already been done, and my own trip was half fun and half pilgrimage. I wanted to visit the place where F3 had – presumably – brought her first kits into the world, and I wanted, after nearly a year away, to be back in mountains that form some part of the mental and emotional landscape of home.

The route into that landscape followed a trail for a while, and then cut away from the trail and up gentle south facing slopes, warm with late summer sun and the scent of dust and pine. At the crest of a pass, the world dropped away, the slope plunging steep and precarious into a narrow pine-cloaked valley that swept back to intersect with the endless marching peaks of the high Absarokas. These north-facing slopes were utterly different from the warm hills I’d just left; I had to edge my way down, dancing between tree trunks for support, the force of gravity and the angle of the pitch propelling me towards freefall. The trees were thick, the shade dense, the temperature so much cooler that I paused to put on my jacket and hat.

Possible wolverine scat under a log, about 0.4 miles from the den site.

As I crouched to pull out my hat, I noticed a huge pile of scat under a log near my feet. I was still a half mile from the den site, but the scat was definitely carnivore and seemed mustelid. It was a bit small, but they were kits, after all. I hadn’t been expecting to collect samples but I did have two ziploc bags on hand, so I shoveled the scat and a large chunk of fur into the bags, GPSed the location, and continued to slide downhill through the dense, cold forest and small open meadows. These meadows were saturated – with streams, with flowers, with warmer patches of sunlight, and with the same breathless silence that hung over the trees. The quiet was ancient and deep and almost tangible, so that I felt like I was diving down and further down through a substance like water, into some other world.

Among all the trees, I wasn’t sure how I would ever find the actual den site, but as I crossed another meadow and stopped to look across the stream that drained it, a patch of pink fluttered from over the water. In May, the crew had tied flagging tape to the tree branches directly above the six entrances to the den. Now, in August, with the snow melted, the tape hung fifteen feet overhead. Beneath the tape, F3’s excavated snow tunnels had led down to cavities sheltered by fallen trees. I’d found the tape, and I’d found the den.

A wolverine's-eye view of part of the den site. The chambers were beneath the downed trees. Note human for scale, and pink tape in tree overhead. This marks the approximate depth of the snow in May.

The crew had already collected all the samples, and I spent a long time simply exploring the area and then sitting and basking in the vast silence. The multiple den entrances had sprawled across an area of approximately 120 m²; the tunnels were probably connected beneath the surface. Beneath the largest of the downed trees on the ground, a hollow against the root ball seemed to have served as one chamber, with two others located among the branches further up the trunk. Against another downed tree, another flattened area between branches suggested a chamber as well.

One of the hollows that was part of F3's den site.

I tried to imagine the family down under the snow in a world of compressed ice, first as newborns and later as more active babies. Did F3 dig new tunnels as the kits grew, or had she constructed the whole network at once? Did she move them from place to place as waste accumulated? At what point did the babies begin to move around through the tunnels on their own? Or did they simply wait, curled up around each other for warmth, where F3 left them when she went out to forage? Had M57 come down here as well? The crew in May had heard his signal and found his tracks crossing their own ski trail; he had traveled directly to the den from the distant location where the crew had heard his signal earlier in the day. If he had gone into the den, what did he do while he was down there? Did he bring them food? Keep an eye on things while F3 was out? (She hadn’t been in the den the day the crew visited.) Play with the kits, add his warmth to theirs, wrestle with them to toughen them up for the outside world? When had they left this place, and did they ever return?

I looked up from the logs, scanned the trees, but everything remained still – no sign of wolverines, or of anything else. The most important ecological question – why here? – remained unanswered, but my personal reasons for being there had been more than fulfilled. I was overwhelmed again by the extraordinary stillness of the place. Later, it came to me that the meadow was suffused with a sense of peace that goes far beyond our normal conceptions of that word – the peace of the Wild, a peace that is so powerful because of its utter indifference to human concerns or moral order, a peace that is edged with on-going loss and ferocity and struggle that are, nevertheless, somehow more acceptable and less alien in places like this. It was, I hoped, a good place to be born a wolverine, and I was profoundly grateful to have seen it.

The Den

Last week, a small crew on skis set out into the high mountains of the Montana wilderness. They were headed into wolverine country, their objective a series of scattered points close to treeline. The points had been obtained during telemetry flights in April, and they indicated that F3, a five year old female wolverine, was restricting her movements to a small portion of her usual range. Under normal conditions, F3 might be found anywhere within an approximate 300 km² sweep of rugged country. Over the past several weeks, however, she had limited herself to a few drainages in close proximity to each other. Her behavior unleashed a wave of excitement among the wolverine crew who had been tracking her since 2007; restricted movement is the classic indication that a female wolverine is in a den with kits.

Determining F3’s reproductive status has become an annual springtime ritual at the Absaroka-Beartooth project, fraught with trepidation, surges of hope, and, inevitably, disappointed resignation to the fact that, once again, the project’s sole instrumented female wolverine has failed to produce kits. We’ve been engaging in this ritual since F3 was first captured in 2007. For the first two years, she was young, and, as far as we knew, there was no male in her territory, so the absence of a den in 2008 and 2009 wasn’t such a surprise.

F3 in 2008, captured by an automatic camera at one of the project's live traps.

Then, in spring of 2009, the Wildlife Conservation Society’s wolverine project took charge of a young male that had been accidentally caught in a bobcat trap in Idaho. WCS released the wolverine, M57, in Montana, and he promptly headed for F3’s territory. We knew that F3 and this male – notable for his white paws and his unprecedentedly relaxed attitude when captured by the project’s live traps – were traveling together throughout 2009, and the tension over F3’s status in spring of 2010 was palpable. For the first time, we had real grounds to hope for babies.

The question was especially urgent for the project because the work done so far had provided no evidence of reproduction in Yellowstone or the ranges immediately to the north, south, and east. In fact, those ranges seemed strangely vacant; the habitat appeared good, but the wolverine population was sparse even for a rare carnivore. Over the course of five years, the project had documented two immigrants to the study area – M57 and a female, F133, who was born in the Gallatins and who traveled across Yellowstone to take up residence south of the park. But there had been no births. This suggests that, at least in Yellowstone and its immediate surroundings, the wolverine population currently depends on dispersing wolverines from further to the north and west. With only a single den documented in Wyoming – in the Tetons – the data also suggest that Wyoming’s population might rely on input from populations in Montana. And with talk of reintroduction following M56’s trip from Wyoming to Colorado, the need for a healthy region-wide meta-population, with as many interconnected nodes of reproducing wolverines as possible, became even more urgent. Any further understanding of reproductive dynamics and denning characteristics – not to mention the sheer and simple fact of more wolverines on the landscape – would be invaluable.

In 2010, a series of telemetry flights eventually indicated that F3 wasn’t denning. We caught her in March of 2010 and were finally able to determine that she was not nursing, although she and M57 were still traveling together. Disappointed, we held out hopes for 2011, but by now the project was officially over and finding resources to keep it going was becoming more and more challenging.

This season, F3 went into the trap early, in January, and the crew noted that her teats were enlarged –  a real reason for hope. The weather remained ferocious throughout the spring, making flights difficult, but when a series of telemetry points finally came in after flights in April, F3’s apparent localization added further evidence to the argument for kits. Finding proof, however, was necessary, and the mission was urgent: wolverine kits leave the den in early May, and the dens themselves, dug in the snow, are ephemeral and nearly impossible to identify once the snow is gone. From the time the points came in, the crew had approximately two weeks to get to the area and figure out what was going on.

The trip in took three hours of skiing, over a steep pass and through heavy snow. At the outset Jason Wilmot, who was leading the trip, listened for F3 and M57 and picked up M57’s signal to the south. There was no indication that F3 was anywhere nearby, and the first point that the crew reached yielded nothing. Jason and the crew pressed on to the next point.

Here, at the pass, they picked up tracks, and then more tracks, and then an explosion of tracks. This, too, was strong indication of a den, and sure enough, backtracking the prints, they found a hole. And then another one. And another. Altogether, the crew discovered six holes in the snow, some apparently linked beneath the surface. The tracks were melted out and the crew were unable to determine whether they came from multiple animals, let alone animals of different sizes. But the evidence for a den and kits was strong.

The crew had already made the decision not to instrument the kits – without the funds for flights to monitor them, it would have placed unnecessary stress on the animals – so they didn’t dig to see if the babies were underground. Instead, they collected DNA samples from the tracks and the entrances to the holes. They listened for F3, but she was still absent. If there were indeed kits, the family might have already left the den permanently, but F3 might just as easily have been out on a foraging run, and the kits could have been curled up in a chamber in the snow beneath the crew’s feet, pondering the strange vibrations of skis and human voices.

Before they left the site, Jason listened again for M57. The signal came in, and it was loud – M57 was somewhere nearby. Employing a trick that wildlife biologists use to determine exactly how close an instrumented animal is, Jason removed the antenna from the receiver and held out the cord with its metal end. If an animal’s signal still comes in without the antenna, the animal is really close. M57’s signal continued to boom in. He was right on top of the crew, probably watching them from somewhere in the trees. As Jason and the remainder of the crew skied out, they crossed M57’s tracks coming into the basin; the wolverine tracks were overlaid on the ski tracks of crew members who had already skied out. From his position far to the south earlier in the day, M57 had traveled directly to the den site. This was further circumstantial evidence that this was indeed a reproductive den, and that M57 was coming to check in on his mate and offspring – a pattern detected on numerous occasions by the Glacier Park and WCS projects.

Without having seen the kits, we can’t confirm that F3 and M57 reproduced. But the evidence is good. From here, we’ll use genetic analysis to try to determine if there are kits and if so, how many. We’ll return to the den site in the summer to gather more DNA samples. If there are kits and if they survive the summer, they are likely to remain within their parents’ territories for the next year, and F3 and M57 are likely to show them all the good foraging spots – including the project’s live traps. We may have the opportunity to capture and examine the kits this winter, to at least determine sex. If we find the funds, we may be able to instrument them and monitor them as they approach dispersal age. This could provide crucial information about connectivity among the different populations, and the extent to which southern populations really are dependent on dispersers from Montana. Overall, it’s exciting and hopeful news for the project and for wolverines at the edge of their range.

Pinatas, Pizza, and How to Meet a Montana Wolverine

Around Easter, a group of pre-schoolers from Billings, Montana, gathered to partake in a peculiar  ritual: they spent the day making pinatas for the animals at the Billings Zoo. It’s peculiar, of course, because what is a wild animal supposed to do with a pinata? But it’s also touching, because it speaks to the fact that someone out there is thinking about these animals in very human terms, and recognizing that they too sometimes crave some entertainment, something out of the ordinary. An animal in the wild is unlikely to encounter a pinata, but it certainly has opportunities for play and exploration that zoo animals lack. The pre-schoolers’ pinatas – a tradition repeated every holiday – are a rough compromise between captivity and the unfettered wild.

The pinatas were stuffed with treats according to the type of animal – fruit and vegetables for the bear, meat for the tigers. Among the other animals, a familiar character put in an appearance: “Some animals use the pinatas as houses. Others, like the wolverine, just rip it to shreds.”

The pinata-shredding wolverine, whose name is Cass, will be a feature at an upcoming showing of Wolverine: Chasing the Phantom at the Billings Zoo on May 20th.  Film producer Gianna Savoie and Cass’ keeper will be among the wolverine-knowledgeable people on hand to help celebrate the wolverine. The film showing honors Endangered Species Day and – perhaps – the wolverine’s new, almost endangered, status. Details are available below, or at the Billings Zoo website.

the poster features F5 of the Glacier Project. The daughter of the famous F4, F5 scaled Bearhat Mountain in the dead of winter for no reason that anyone can determine, other than the sheer adventure of getting to the top. She later died in an avalanche, a true mountaineer to the end.

The poster features F5 of the Glacier Project. The daughter of the famous F4, F5 scaled Bearhat Mountain in the dead of winter for no reason that anyone can determine, other than the sheer adventure of getting to the top. She later died in an avalanche.

If zoo animals shredding pinatas aren’t enough for you, you can head east from Billings; the Detroit zoo regularly supplies its animals with specialty pizzas as part of a program to provide entertainment to the zoo’s denizens, and offer inner city kids the chance to visit the zoo. Detroit has two wolverines, a male, Jigi, and a female, Luka. In case you ever find yourself taking a pair of hungry wolverines to an Italian restaurant, check the menu for a peanut-butter-honey-sardine-raw-meat-and-bones combo. Yum. The zoo keeper describes the two wolverines  eyeing each other’s pizzas before settling for their own: “Whatever they have, the other one is always better. They’re just like kids.”

Wolverine eating a bones-and-raw-meat pizza at the Detroit Zoo. Source: Detroit Free Press.

Finally, another important graphic: a shot of snow cover across the US from earlier today. Winter in the Rockies has been ferocious this year, and as this graphic demonstrates, most of the snow on the ground is over five feet deep. It’s been a good year for wolverine denning conditions.

Valentine’s Day and Mother’s Day are the bookends of the wolverine denning period, and this is the week that wolverine kits around the globe are emerging from their snowbound existence and heading out into the wider world. F3, our female in the Absarokas, was thought to be in a den as of flights in late April. Last weekend, a field team went in to investigate the site and determine whether she had actually given birth or, as per her notorious reputation, was fooling us once again. I really despise cliffhanger journalism, but the topic deserves a post of its own. So check back later this week for the story of what the team discovered.

Snow cover in the US, as of May 10, 2011.