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.

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!

 

New Study on Food Storage and Reproduction

Wolverine kits, at least several weeks old. Borrowed without permission from care2.com. Too cute not to repost.

For years now, we’ve known that wolverines are found in regions of deep spring snowpack and low summer temperatures – Copeland et al’s 2010 paper elucidated this elegant model of wolverine distribution by mapping known wolverine locations from all over the globe and placing these locations onto a map of global snowpack on May 15th, and maximum August temperatures of less than 22 degrees Celsius. The paper showed that wolverines are tied to the cold regions of the northern hemisphere, and linked this dependence on cold to the fact that wolverines give birth in snow dens. The paper was groundbreaking and its publication eagerly anticipated, because it provided enough evidence of climate change threat to support the USFWS’ 2010 decision that wolverines are warranted for listing.

A new paper in the Journal of Mammalogy by Bob Inman, Audrey Magoun, Jens Persson, and Jenny Mattisson expands our understanding of the links between wolverines and the cold, exploring the complex reasons for the evolution of wolverine reproductive timing and behavior.  If the Copeland paper told us that wolverines are indeed climate sensitive due to denning requirements and a cold-adapted physiology, this paper asks why those denning requirements and physiological limits are so strict – in other words, what adaptive advantage does cold-climate specialization offer to the species?

Inman and his co-authors suggest that the wolverine’s strategy is driven by the nutritional needs of the species, and of reproductive females in particular. Pregnancy and nursing are the most nutritionally demanding activities that any wolverine – any mammal, in fact – undertakes, and the successful rearing of young requires a secure source of food. The timing of wolverine births early in the year, according to the paper, allows females to take advantage of a flux of winter-killed ungulates that they have cached, and the nursing and weaning periods encompass the spring surge in baby ungulates and the brief summer explosion of small mammal populations. Persistently cold climates allow wolverines to cache food in an environment where it won’t go bad, allowing them to store sparse nutritional sources and “be efficient in channeling available food resources towards reproduction.” And, suggest the researchers, by living at the outer – or upper, in the case of the Rockies – margins of the ranges of other predators such as wolves and bears, wolverines avoid direct competition with much larger and better equipped rivals. Put all of this together, and wolverines obtain a neat set of advantages by living in a harsh and desolate landscape.

The paper relies on synthesis of existing research, and contains a great section reviewing all the data on reproduction. Wolverines mate in summer, but implantation of the fertilized embryos is delayed until winter. We generally say that wolverines give birth around February 14th (Valentine’s Day) and that the kits are weaned by May 15th (Mother’s Day), because these dates are easy to remember and are, on average, accurate. But in the details of known wolverine birth dates, we see a much wider range, with some wolverines giving birth as early as January, others as late as April. This means that implantation – nidation, in scientific parlance – also occurs over a range of dates, from November through January, with a 45-day gestation. Most of the births do occur mid-February to early March, but the range offers the possibility that female wolverines are responding to environmental factors on a year-by-year basis (several of the females were monitored over several years and had different chronologies in different years.) Does this mean that wolverines might possess some latitude in timing births to correspond to changing snow and nutrition availability over the longer term? Like almost everything else about wolverines, we have no definite answer, but it’s interesting to think about.

The paper also summarizes reports in some studies of very high levels of wolverine pregnancy (implanted embryos). This, too, is interesting, since female wolverines seem to raise very few litters. The data suggest that many females who give birth lose their litters early. Nutritionally, this is more adaptive than struggling to keep a litter alive and then losing it later, since it represents a much smaller investment of resources. Losing a litter early during a year when conditions are sub-optimal gives females a chance to maintain better body condition for next year’s litter, when conditions might be better. All of the attention to this question of reproduction is critical, since we absolutely must understand these dynamics in order to determine effective conservation strategies.

This paper received a fair amount of attention in the press, most of it focusing on food storage: here at the Examiner, at the Huffington Post, at LiveScience, at USA Today (there is, perhaps, a wolverine fan on staff there, because this makes two articles on gulos in two months), at National Geographic, and at MSNBC. I’m sure that there are others out there, too. Most of these articles quote lead author Bob Inman, of the Wildlife Conservation Society, sounding very respectable and scientific – but his secret identity is revealed in an article discussing whether or not the ubiquitous presence of Wolverine the X-Men superhero may also be an adaptation to climate change, in which Wolverine uses his extensive social connections as a food storage strategy: “Understanding why and how Wolverine exists where he does and the various adaptations he has evolved to eke out a living will better inform population management strategies and conservation of the comic industry,” said researcher Robert Inman. I’d heard that Bob was away in Sweden for several months, but now we know the truth.

My own summary of this paper is delayed; I usually like to talk to the scientists to make sure I have all of the implications correct, but the paper came out just as I left for Mongolia, and I haven’t had the chance to talk to anyone. So this is just a basic summary. More later.

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.

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.

Break out the Champagne! (Tentatively….)

The sky finally cleared enough last week to get two flights into the air, on Wednesday and Saturday, and F3 was in the same location for both flights!

We’ve tentatively concluded that she is indeed localized and that this, along with evidence of pregnancy when she was caught in January, suggests that she has kits. The pilots observed a large number of tracks in the vicinity of the signal as well. With wolverines, assumptions can get you in trouble, so I’m trying not to invest too much in the idea of these kits until someone has actually seen them. But the evidence points to a new family of wolverines in the Rockies.

A field crew will ski in to investigate and perhaps set up a camera at the site. We probably won’t instrument the kits; the project is currently at a low budgetary ebb and we lack the funds to regularly fly and monitor kits, which would be necessary to gather the data that telemetry could provide. This is unfortunate, since dispersal is one of those critical parameters for understanding population dynamics, especially in this tiny population node at the very edge of wolverine range. A site visit and a camera will allow us to determine how many kits F3 has, and perhaps their sex, and may even offer some information on whether M57 is visiting the den, and how often.

I am simultaneously thrilled – we’ve been waiting years for F3 to have babies – and a little disappointed – I am currently out of the country and won’t be able to participate in the den visit. But the disappointment is all selfish, and the excitement is absolutely overwhelming.

Further exciting gulo news came out of Oregon today – after researcher Audrey Magoun tracked a wolverine in the Wallowa Mountains of eastern Oregon last week, her camera traps captured images of two individuals in the same area. Audrey and her husband have reset the camera stations to photograph the animals in a way that will allow them to determine the sex of the two animals.

After years of sighting reports from Utah, WCS did surveys last year and picked up tracks in the Uintas; the tracks looked like wolverine tracks, but they couldn’t confirm the ID. This winter, a Forest Service biologist found and documented a set of tracks in the Uintas as well, and the photographs suggest that Utah does have at least one wolverine after all. Where did this wolverine come from? This is one of the reasons we need the capacity to monitor kits.

Further to the north, in Canmore, British Columbia, researcher Tony Clevenger is gathering DNA samples by way of hair snares to study Canada’s wolverine population. Canada’s wolverine population is more robust than the population in the US Rockies, but Clevenger and his colleagues are trying to estimate population numbers and determine whether the animals are being affected by infrastructure development.

All around, it’s been a great week in the gulo world. Now I’m looking forward to hearing about the kit expedition, and having final confirmation that F3 and M57 have babies.  (By the way, do people really celebrate the birth of a human baby with champagne? Or is it cigars? Or something else? I can’t remember. In any case, I am proposing that the birth of wolverine kits be celebrated with champagne henceforth….)

A Real-Time Snow Map for Armchair Wolverine Research

2011 may go down in history as the Year of Snow; it seems like all of North America was bombarded throughout the winter.

Now that spring has officially started, however, and now that wolverine dens are the biggest thing on wolverine fans’ minds,  it’s time to start watching the really important snow trend: how long the snow remains on the ground.  Does it stick around in your area of interest long enough for a female wolverine to den? A  real-time snow map allows the viewer to see how much snow cover currently exists in the United States (unfortunately it doesn’t extend to other countries, not even Canada). Fans of Jeff Copeland’s and the Rocky Mountain Research Station’s work on the link between wolverine distribution and snow cover can follow in the footsteps of some great science and conduct their own monitoring via this site.

 

Real-time snow cover map of the US, January 29, 2011.

Real-Time snowcover map of the US, March 23, 2011

If you’re wondering if wolverines live in your area, check back at this site in mid-May. If you’ve got snow on the ground at that time, it’s a possibility. If not, wolverines probably aren’t breeding nearby.

As spring progresses, this map should also give a good illustration of the meaning of the phrase “meta-population inhabiting islands of habitat in the Rockies.” Screenshot the page on May 15th and you’ll have a rough picture of where those islands are….and how widely they’re separated.

In cropping these screenshots, I realize that I actually cropped out the key – the areas of light pink indicate the highest level of snowpack, 60+ inches, while the light blue represents snow cover of about 1 inch. For wolverine purposes, reproductive habitat is probably indicated by areas that currently have 60+ inches of snow on the ground – gulo dens are deep.

Week Four in the Life of a Kit

A German engraving of a mother "veelvraat" and her kits.

Somewhere among Montana’s high peaks, a female wolverine is curled around her two kits. The babies have more than doubled in size since they emerged into the world about a month ago, pure white and barely big enough to fill a human palm. Their fur has darkened now to a pale gosling gray across their bodies, and to a rich chocolate brown around their eyes and noses. Their ears are still flat to their heads in the way of small animals, and their tails are fuzzballs. Their feet still seem tiny, no hint of the gigantic snowshoes which will eventually carry them across thousands of miles of rock and snow and ice.

These pale, fluffy infants have spent most of their first four weeks nursing and sharing warmth with each other and their mom. When she leaves to hunt or scavenge, they are insulated by the snow overhead. The den that they occupy is buried beneath at least ten feet of snow – probably more – amid the tangled branches of downfall or a warren of talus, and accessed by a series of narrow tunnels that the female wolverine has excavated. They are safe from any but the most persistent, reckless predator. Their mother is gone for only hours at a time, and she returns with a stash of snacking material – the femur of an elk killed during hunting season, a chunk of meat from the carcass of a mountain goat that slipped from a cliff, a duck that, lost in a storm too far north during migration, froze to death and was buried in the snow. Occasionally, the kits’ father visits the den, perhaps marking the entrance to let any other wolverines know that the babies inside are defended, and maybe even venturing down into the tunnels to visit his mate and babies.

Hopefully, this is a portrait of F3’s and M57’s family life right now.

March is a big month for wolverine researchers who think that one of their female gulos might have gone maternal. This is when we begin the tough work of trying to figure out whether the wolverine in question has actually denned and produced kits. Despite many efforts to develop a non-invasive method for answering this vital question, the most reliable way to figure it out remains instrumenting the animal earlier in the year and then flying replicate flights within the first month of the denning period – which begins in mid-February – to see if she’s localized. Few things keep a wolverine in one place, so if a female is “observed” via telemetry in the same location over three consecutive days in March, she’s probably in a den.

F3 should be among these new mothers, but some additional information has complicated the usual uncertainty. When F3 was captured in late January of this year, her teats were noticeably enlarged. We figured that this meant that she was pregnant, and that teat enlargement begins at nidation, the point at which the fertilized eggs implant in the uterine wall and begin to develop. Some folks with wolverine experience have suggested, however, that teat enlargement doesn’t begin until the female gives birth. F3’s teats this January were not large enough to suggest that she was actually nursing at the time of the capture, but large enough to suggest that something reproductive was happening – or had, within the past year. Yet when we collared her in late March of last year, her teats were so flat that they were nearly non-existent (Apologies, F3, but I’m assuming that given the badass gulo attitude, wolverines don’t have a sense of modesty about such personal attributes….)

This means one of two things: that teat enlargement does begin at nidation and that F3 had babies this year; or that teat enlargement only happens once a wolverine gives birth, and that F3 had kits last year – sometime in April or later. The latter scenario would be utterly unheard of, far later than a wild wolverine has been recorded giving birth before. I did a quick search through the literature, and couldn’t find anything conclusive about  the physiology of wolverine nursing, so I don’t have any definite information on which to base an answer.

I would be shocked if she had had kits last year, but there is one other complicating piece of information. On the day that trapping season closed showing no wolverines taken in Region 3, a trapper called in to report that he had killed a small female wolverine in the the Absarokas. For a while, we were convinced that this was F3, because the wolverine was taken out of an area close to F3’s territory, but the dead animal was apparently very young, and we eventually confirmed via telemetry that F3 is still alive. Given the exclusivity of wolverine territories, F3’s tolerance for another female within her kingdom would be strange – unless it was her yearling daughter. And then it would make perfect sense.

F3 dropped last year’s collar a few weeks after we put it on her in March of 2010. This collar would have encompassed the critical time when she might have been raising these phantom kits. We retrieved the collar in late summer of 2010, brought it back to the office, and plugged it into the computer. The collar had malfunctioned; it contained no data. F3, who, as I’ve said before, somewhat embodies the trickster-ish nature of her species, managed to keep us at bay once again.

This mystery should be resolved with flights over the next few weeks, hopefully showing that F3 is indeed up there in a den, nursing kits and preparing them for a wild life in the mountains. But really, keeping track of F3 wouldn’t be worth it if she didn’t keep us guessing.

Film festivals, baby wolverines, and an impending glacierless century?

For the past two weeks I’ve been meaning to write about a conversation that I had with Gianna Savoie about her documentary Wolverine: Chasing the Phantom, review Doug Chadwick’s book The Wolverine Way, and post a synopsis of Jeff Copeland’s snow model paper. But last week I learned that I’d received a substantial grant to return to Mongolia to look for wolverines there (!) as part of a longer term, large scale study of wildlife and climate change, followed quickly by a series of conversations about a possible PhD associated with the upcoming Mongolia research. Added to a carnivore conservation meeting that NRCC will be facilitating in Montana, and an absolutely necessary diversion choreographing and filming a Bollywood-esque dance number in support of river conservation with a bunch of friends over the weekend, my head has been spinning (literally, during the dance; figuratively for the rest of the time.)

The Wildlife Film Festival is underway in Missoula, Montana this week, and Gianna’s film is showing tomorrow, Thursday the 13th, at 12:30, and on Saturday the 15th at 5:30. The film won a ‘Made in Montana’ award and was also recognized for outstanding scientific content. And it also features some of the only footage you will ever see of live wolverines. The schedule is available at the film festival’s website. PBS will air the documentary in November, so if you can’t make it to Missoula this week, keep your eyes open for the film this fall.

The Missoulian published an article today about Glacier National Park’s centenary. 100 years after its founding, Glacier’s namesake features are nearly gone. Glacier hosts what is probably the most robust wolverine population in the Lower 48, and the ecological shifts that are occurring there as a result of climate change could have serious effects on wolverines throughout the Rockies, not to mention a host of other high-altitude species.

Finally, in my few opportunities to check on the blog over the past week, I’ve noticed that a number of people have arrived here in search of information about and pictures of baby wolverines. In fact, over the existence of this blog, ‘baby wolverines’ and searches for information about reproduction are some of the most common terms leading people here. So if any of you arrive here looking for information about wolverine kits, I think it’s great, and I’m curious – is a class somewhere doing a project on wolverine ecology? Or are people just generally interested in baby wolverines? I would love to know, so leave a comment if you happen to be so inclined. For the best information on all aspects of wolverine life history and ecology, organized in a way that is much more accessible than a blog, please visit The Wolverine Foundation’s page on life history. There are links there to information about denning and reproduction that you will find interesting. Unfortunately there aren’t so many great pictures of baby wolverines out there, but I promise to do my best to take some if I ever stumble across a den.

Den Search

A few weeks ago, Jerry Longobardi,  Wyoming Game and Fish game warden for Teton County, came across a hole in the snow on the west side of the Tetons, with wolverine tracks leading into and out of it. Photos of the site circulated among WY Game and Fish, WCS, and NRCC, and the verdict was clear: they were wolverine tracks. The critical question was, was the hole a den, or did it simply represent a food stash, or a curious wolverine digging in the snow for a rodent?

The hole, with wolverine tracks

WCS ran a research operation in the Tetons for many years and documented what to date remains the only confirmed instance of wolverine reproduction in Wyoming, also on the west side of the Tetons. WCS is still the primary research organization for the Tetons even though they are not currently operating traps here. But because their operation is based in Montana, coming down to Jackson to investigate the site would have been a haul. I volunteered to ski in with Jerry a few weeks after the original sighting, to see if the area was still being used and, if it was, to try to collect DNA samples by picking up some scat. We set out on Friday. It had been snowing heavily for the past six days, pure wolverine weather, and as we headed west, the prospect of finding a den buoyed my spirits more than the first glimpse of sunshine in a week.

The chances of stumbling across a wolverine den by accident are minute, and den detection remains one of the elusive objectives of most wolverine research projects. An instrumented female will provide a location by localizing – staying in one spot for a number of days – which wolverines seldom do unless they are denning. But detecting dens this way requires a trapping operation before the denning period, reliable capture and instrumentation of female wolverines in the region, and the money and skilled pilots to fly repeat telemetry flights in rugged mountainous terrain three times a day over the course of four days at the beginning of the denning period. If all of these circumstances come together and the instrumented female is picked up in the same location over the course of the four days, then you know you have a den. This method is time consuming and expensive, due to the front-end investment in trapping in remote locations, and the costs of telemetry flights. For years research operations have tried to develop flight-based surveys for dens, but despite the Absaroka-Beartooth Project’s success in developing a flight-based systematic survey for presence-absence of wolverines in a given region, no one has been able to reliably locate dens of uninstrumented females from the air. So finding a den by any means other than telemetry is rare.

The site, as pointed out on the map, was not in what I would have considered denning habitat – generally, one thinks of a mother wolverine choosing to situate herself in a high cirque, and the forested ridge where Jerry had come across the hole didn’t seem quite right. But then again, what do we really know about wolverine denning habits in the Tetons, with only one den ever discovered? Besides, I wanted it to be a den, so I suspended judgement and remained optimistic.

We took a snowmobile for the first few miles and then skied in from there, not wanting to disturb the wolverine, if she was there. GPS coordinates led to a swath of snow on a steep hillside,  where despite high hopes, there was no further sign of disturbance. We removed our skis and slid down the slope to investigate for tracks, but there was nothing. My heart sank almost as deeply as I did – the snow was thigh deep and I plunged through the bottom of the snowpack and snagged my foot in a tangle of branches. In the struggle to extricate myself, I ended up upside-down, head pointed downhill. It might have been a dangerous situation if I’d been alone, but it also illustrated that this could indeed be denning habitat. Wolverines seem to favor slopes underlain by either sizable talus, or downfall. It seems that they dig into the snow for access, and use the cavities formed by the boulders or trees to provide structure to their dens. The hollow that I’d fallen through, and the branch that had snagged my foot, would be perfect for a wolverine. And the depth of snow, along with the cover provided by the forest, suggested that the snowpack would probably be adequate to provide necessary cover through mid-May, when wolverine kits are finally independent enough to travel on their own.

We dug into the den site until we hit ground, but found nothing – no sign of bones or of anything else a wolverine might have been eating. Jerry had found a second hole several hundred yards uphill from the first, so we skied up to investigate that as well. Again, there was no sign, and because the snow was terrible, we called off further searching and headed back.

Later, Jason said that the lack of tracks didn’t necessarily mean that it hadn’t been a den. Female wolverines generally occupy a series of dens in the course of raising their kits – a natal den, in which the kits are born, and successive maternal dens, in which the kits are nursed, raised, and eventually weaned. Jason estimated that a mother wolverine moves about 300 yards between den sites – which was approximately the distance between the first hole that Jerry found, and the second.

Even if it wasn’t a den, Jason suggested that it would be a good idea to go back and dig more extensively to see if we could uncover some sign of what the wolverine might have been doing in the hole. Food habits data, while not quite as thrilling as the prospect of finding a den, are also rare and valuable.

We’ll give it a few weeks, and then I’ll head back up to check out the site again.