Last Monday the Absaroka-Beartooth Project’s female wolverine F3 went into one of the project’s live traps in Montana. Jason Wilmot, Jeff Copeland, and several other participants drove up to re-instrument her. It was an early-season capture; usually wolverines hit the traps hard starting in March. Not for nothing are wolverines referred to as gluttons, so it’s hardly surprising that a gulo would grab an extra bite at any time of year, but a possible spur to F3′s early trap raiding became evident when the crew saw that her teats were enlarged; F3 is probably pregnant!
We captured F3 late last March and had to search through the fur of her belly to even find her teats; disappointingly, they were nearly non-existent, meaning that she was probably not pregnant and had not given birth last year. Understanding reproduction is the crux of the question of a species’ status, and with wolverines, data on reproduction are notoriously hard to obtain. Beyond the statistics, of course, a birth in any rare species is cause for celebration. F3 is about five years old, and although female wolverines reach sexual maturity at around two, most don’t reproduce until they’re three or four. We had high hopes for F3 when M57 moved into her territory two summers ago, but last year, although they had been in each other’s company during the breeding season, no kits appeared.
This didn’t mean that they hadn’t mated; wolverines, like other mustelids, bears, and several other mammal families, have a system of resource-governed pregnancy known as embroynic diapause or delayed implantation. A wolverine may mate and the eggs may be fertilized, but they don’t implant and develop until months later. If resources are too scarce and the female isn’t in good enough condition to bear and nurse young, the embryos dissolve without implanting.
Presumably in wolverines this reproductive strategy helps deal with the fact that the animals are sparsely distributed over the landscape; who knows when you’re going to meet again, so you might as well make every effort to insure the future of the species when you do run across each other. Delayed implantation probably also helps female wolverines cope with the sparsity of resources in their severe habitats; reproduction is hugely energetically expensive for any animal, and if the environment isn’t able to support a female through the intense periods of pregnancy and nursing, it makes no sense to put the energy into giving birth to young that will probably starve. Delayed implantation is a strategy that allows wolverines to fine-tune births to the best possible conditions for reproductive success.
Once implanted, gestation is quick, between a month and six weeks. The kits are born around Valentine’s Day, usually twins but sometimes up to four, deep in a snow den that the mother excavates. They are tiny, pure white, and helpless. A man who has kept captive wolverines for many years and has successfully facilitated a number of births says, as related in Doug Chadwick’s The Wolverine Way, that the kits are born with some sort of waxy substance on their fur and that this substance smells so horrible that it’s hard to get close to a newborn wolverine without getting nauseous. Presumably this, along with 10-foot-deep snow dens, is a defense against predation while the kits are vulnerable.
Female wolverines nurse their young for about three months, moving them among a series of dens before they emerge around mid-May. By this time, they are unrecognizable as the tiny white creatures born in February; they already have full gulo coloring and are close to adult size. They are not quite independent yet, though, and they stay with their mom through the fall. For the next year, still not quite ready to be on their own, they roam their parents’ territories and sometimes rejoin each other, their mother, or their father to play, to learn how to find particularly good carrion, to get some tips on hunting ground squirrels, or simply to pursue the mysteries of wolverine life in company. At the onset of full adulthood, around age two, they set off to carve out their own territories – if they survive. The Glacier National Park Wolverine Project recorded rates of juvenile mortality at around 50%; the world is a perilous place for a young wolverine. And then, even if a young wolverine makes it to its own new territory, it might still face what can be referred to as the M56 Dilemma; travel 500 miles across all kinds of obstacles, only to discover that the new territory is a little too vacant, and that there are no mates to be found.
Add to all these contingencies the fact that a female wolverine at peak condition and with all the resources she needs generally only produces kits every other year, and the survival of the species at all, let alone among widely separated mountain ranges, begins to seem miraculous.
The title of the blog post is something of an inside joke, because while I’m sure that giving birth provides its own sense of gratification to the female wolverine involved, wolverine researchers also have a distinct experience around wolverine pregnancy, and that experience seems primarily to be one of extreme uncertainty and a total suspension of expectations. The chain of uncertainty goes something like this:
Great! We have a male and a female wolverine hanging out together! Will they mate?
Okay, so if they mated, will she become pregnant, or will she resorb the fertilized eggs?
Wow, it looks like she might be pregnant! Will she manage to successfully den? Will she even give birth, since wolverines known to be pregnant in Glacier later appeared not to have had kits?
If she successfully dens and gives birth, will we be able to tell that she’s denning?
If she is denning, and even if we know she’s denning, will she be able to successfully nurse her kits until May?
If the kits live, it’s imperative to instrument them, because this will provide absolutely critical data on dispersal – but can we find the den?
If we find the den, do we have anyone seriously hardcore enough to get to it?
If we find the den and instrument the kits, will we be able to successfully track them, or will they disappear from the airwaves like so many other juveniles wolverines have done before?
Even if we have the human and technical capacity to do all of this, do we actually have the funding to pay for collars, implants, flights, and salaries?
These questions, no doubt, result in a number of sleepless nights for the expectant researchers; since the big news came in last week, I’ve already chalked up two. Wolverines are tricksters, and F3 in particular has had an uncanny knack for raising our hopes and then smacking them right back down. The uncertainty, though, is tempered by moments of euphoria, because if she is pregnant, and if she gives birth, and if we can instrument and track the kits, it’s a huge set of information on how wolverines function as a meta-population in the Rockies. Huge. And it’s worth all the uncertainty and the sleepless nights and the frozen fingers and toes and the near-death experiences if it can help in some way to tell us how to keep the species on the landscape over the long term.
So, F3 and M57, congratulations on your big news….if your big news is really the big news that we think it is. We will be eagerly waiting to find out.