Tundra lemming populations plunge to near-extinction like clockwork every few years, only to rebound. By Matt Barron

It's a familiar story: lemmings breed themselves into frenzied numbers until, driven by panic, they hurl themselves off a seaside cliff in a kind of hysterical group suicide. In 1958, this image was burned into pop-culture consciousness by a Walt Disney documentary that showed the downy brown rodents scurrying in packs toward a rocky cliff, then diving into the ominous waters below.

“It was all a fake,” laughs Charley Krebs, an ecologist who’s devoted most of his working life to solving the lemming riddle. “But you don't speak badly about Walt Disney or you're put in purgatory.”

Disney’s White Wilderness went on to win an Academy Award for best documentary feature, despite the doctored suicide scene. The filmmakers reportedly imported a batch of lemmings from the eastern Arctic, transported them to a riverside cliff in Alberta – far outside the lemming range – where the rodents were neatly herded over the cliff edge.

Though Krebs helped debunk the suicide-myth decades ago, the 70-year-old scientist is still chasing the elusive theory behind the rodents’ dramatic – almost operatic – population swings that see their numbers soar and crash with utter regularity and for no apparent reason. At an age when most of his counterparts are taking in cruises and cottage-living, Krebs heads out on the treeless tundra again this summer to test his latest theory, trying as he has for more than 45 years to wrest an explanation from the Northern wilds. The way he sees it, since almost every carnivorous tundra beast and bird at some time or another feeds on lemmings, “if you want to understand the North, you have to understand the
lemming.”

**

Lemmings are rather unspectacular-looking rodents, more guinea pig than mouse, puffy with a splashy chestnut coat and dagger-like incisors. The warm-blooded creatures thrive across the treeless Arctic sweep, managing to survive the harsh winter by burrowing in an endless network of underground snow tunnels, which they excavate with paddle-shaped claws on their forefeet. Their stubby ears, legs and tails help cut down on heat loss, while their white winter coat keeps them well hidden from predators. Though lemmings dwell underground during winter, you can sometimes spot them skittering across the snow, especially during their clockwork population spikes, when the tunnels are crowded.

For reasons Charley Krebs is still probing, every three to five years lemming populations explode up to 500 times, crash to near-extinction, and slowly climb back up again. Inuit have long noted these population eruptions, and 19th century Hudson’s Bay Company fur-trapping records show them, too, regular as ECG heart readouts.

These lemming explosions have perplexed ecologists for almost as long: how can they possibly understand how populations work, if they can't explain the lemming roller coaster? After all, the rodents’ cycle controls the pulse of Arctic life, providing prey to everything from Arctic foxes and ermines to gyrfalcons and snowy owls, and all other tundra carnivores for that matter.

It’s unsurprising, then, that this confounding tundra critter has spawned a host of competing theories into its drastic population swings. Some scientists point to the lemmings' environment, namely the abundance of the grasses, willow, and Arctic cotton they subsist on, or the prevalence of their predators. As the theory goes, an ecosystem flush with hungry Arctic foxes will wipe out lemmings. When lemmings are scarce, so too become foxes, which allow lemming numbers to climb again. Other theories suggest a complex genetic process triggers their seemingly counterintuitive population dives. Krebs, though, doesn’t buy any one theory, which is why he’s still chasing what some ecologists call the holy grail of ecology. Having given chase for four decades, Krebs once joked: “I suppose it's better than getting hooked on smoking.”

**

Born in small-town Illinois, Charles “Charley” Krebs was already poring over ecology books when he was just eight years old. He held an immediate fascination with the Canadian Arctic and its mysterious lemmings. “Did they really did jump off cliffs?” he wondered.

After earning a biology degree from the University of Minnesota, Krebs’s lemming fascination drew him to the University of British Columbia to study alongside Dennis Chitty, who remains the world’s leading lemming expert. In the late 1950s, a young, determined Krebs made his first field foray, live-trapping lemmings on the sky-lidded tundra near Baker Lake in present-day Nunavut. His findings both stymied and compelled him. For instance, in summer – a brief but fierce growth period in the North – lemmings stopped breeding.

Confounded and still thoroughly unconvinced by the simple predator-theory extolled by many of his colleagues, Krebs trudged back into the field, never one to test theories in a lab or hypothesize in his office as many ecologists have done. Instead, he’s set himself the intractable task of always testing theories in the wild. His dedication to field work has led to some groundbreaking conclusions – and time-gobbling detours.

In the mid-1970s, by this time an award-winning and well-known ecologist, Krebs’s lemming research took a left turn. Halfway into his career and well into his 30s, Krebs boldly launched a 20-year study on snowshoe hares, with the hope that understanding the hare cycle would shed light on lemmings. (Hare populations soar and crash in the same way.)

It would be an epic undertaking involving some 500 traps that Krebs and his crew had to check every week for a period of 10 years. Krebs had his technicians plod the Yukon’s vast Kluane Range for kilometres on snowshoes, lugging 20-kilogram bags of feed over their shoulders to test whether food abundance would keep hare numbers from plummeting. Not one to slough his work off on eager students, Krebs would show up year-round with his signature goatee, round glasses and monstrous work ethic. Labelled a workaholic by his mentor, Chitty, Krebs would work tirelessly at Kluane for weeks, even months, rarely taking breaks. Described as patient and “very kind” by some, intimidating by others, few could debate his friendliness or bone-dry sense of humour – or his frustratingly uncompromising nature.

One summer during the marathon hare study, Krebs and two students had been live-trapping animals on a tiny island in Kluane Lake when a severe and lengthy storm broke out. The lake flared into waves too large for their tiny boat to navigate and left them trapped on the island. Their meager three-day food supply quickly ran out, and after nearly a week without food they jerry-rigged fish hooks. But nothing bit. Starved and tempted by the ample, well-fed hares bounding around them, student Carlos Galinda-Leal suggested eating one of animals. Krebs refused. Plucking one hare from the island would disturb the population studies. The students pleaded with Krebs, and he eventually agreed – but only if the chosen hare wasn't part of the study. The students knew of course that most of the hares had been tagged. The following day they caught a hare – but sure enough, its ear was tagged and Krebs wouldn't let them kill it. They had waited this long, he said -- surely they could wait one more day. Luckily, the storm soon calmed and the hungry trio high-tailed it back to shore.

Today, Galindo-Leal, a professional biologist who’s worked for 26 years alongside several big names in ecology, can laugh about the scenario. He says, in a tone of amazed admiration, “I've worked with other famous ecologists. But I’ve never met anyone like Charley Krebs, anyone who’s that devoted.”

That devotion helped Krebs and his colleagues complete what would become a landmark study of the Yukon’s boreal ecosystem. But after 20 long years of work, Krebs concluded that hares were “the most boring animal on earth,” and their cycles seemed to have different causes than the lemmings’. Predation and food play a role, but not the aggression and territoriality ecologists now think lie at the heart of the lemming cycle. “This was, in a sense, a disappointment,” Krebs says, in his slow, methodical way of speaking, as if he's putting a measuring tape to his thoughts. “But what can you do? You take what comes.”

**

After two decades focusing on hares, Krebs turned back to lemmings. Only this time, he looked beyond his usual study area. In 1999 he was one of 31 scientists selected to join a Swedish polar expedition threading the High Arctic from Baffin Island to the Yukon coast. That summer, the red-and-white Louis St. Laurent icebreaker ferried the scientists from site to site. Unsurprisingly, Krebs was out there trapping as many lemmings as humanly possible.

Since small-mammal populations have long been known to rise and fall simultaneously over great distances, Krebs wanted to test the scale of this so-called synchrony. After crunching the data, he found that, indeed, lemming and vole population cycles were in sync across the eastern Arctic – but strangely, not throughout the west. This ecological discrepancy is what’s fuelling Krebs’s latest research endeavour. This summer, “semi-retired,” Krebs will work with a team of ecologists from around the world to simultaneously study lemming cycles across the circumpolar Arctic.

After testing predation, food abundance and genetic predisposition, Krebs is also tackling the issue of overcrowding, which prompts some ugly behaviour among lemmings. When things get too cozy and cramped, lemmings are known to kill their neighbours' young to make room for their own, something family-friendly Disney probably wouldn't touch.

“Infanticide is something no one likes to talk about,” Krebs says. “But it happens in rodent populations.” Infanticide might explain why lemmings suddenly stop breeding in summer, as Krebs witnessed 46 years ago during his first field studies. The lemmings’ scrappy demeanor may also contribute to the theory. “Basically, a female looks around, speaking metaphorically, and thinks, ‘Oh my god, there's no point in having more babies because they'll only get killed.’ So she’ll quit having then and wait until next year.”

But this is only part of a phenomenon so complex it sets the brain bobbling. After decades of dedicated study, Krebs has concluded that there’s no one grand reason for lemmings’ erratic population swings. The answer lies in a meaty broth of multiple ingredients – overcrowding, infanticide, predation and food. “What's going on out there in the real world is more complicated than anybody wants to think about,” Krebs says. “We like to think the world is really simple – that human beings are complicated and everything else is simple. But that's just wrong. To sort out what seem to be these straightforward problems takes a very long time.”

Four years ago, three European biologists relatively new to the lemming puzzle boldly claimed to have finally solved the mystery: quite simply, that predators alone drove the cycle. Their study on lemmings in Greenland was published in Science to much media excitement. Krebs just shakes his head. “It's crazy, but they're entitled to their opinion,” he says. While he believes predators do play a role, Krebs says the scientists have ignored all the other factors, ones he’s been trying to untangle for decades. Without a trace of bitterness, he adds, “They're young. They haven't been doing this for 40 years.”
For Krebs, the time has been well spent, and his lifelong quest became a labour of love that grew beyond the pursuit of an answer. “You fall in love with your animal in some weird way,” he says. “People like their dogs and cats; biologists like their lemmings and hares. They’re absolutely beautiful.”

Matt Barron is a freelance writer based in Saskatoon.