Wolf Teeth Reveal a Hidden Cost of Warmer Winters

Some of the wolf teeth that Amanda Burtt examined have been sitting in museum drawers since the 1840s. They were pulled from British caves and gravel pits by Victorian collectors who had no concept of climate change, no electron microscopes, and certainly no idea that the scratches on a molar could tell you what an animal ate for its last few meals. Nearly two centuries later, those scratches are telling a story that wolf conservationists probably need to hear.

Burtt, an Honorary Senior Research Associate at the University of Bristol, and her colleagues used a technique called dental microwear texture analysis — DMTA for short — to read the microscopic pits and gouges left on wolf tooth enamel by food. Hard items like bone leave deep, complex pitting; softer foods like flesh produce finer, more parallel scratches. It is, in effect, a dietary diary written on the surface of a tooth, recording roughly the last weeks or months of an animal’s life. Researchers sometimes call it the “last supper” effect.

The team compared three groups of grey wolves. The oldest, from around 200,000 years ago, lived during an interglacial with summers broadly similar to today’s but winters cold enough for seasonal snow. The next lot, from about 125,000 years ago, experienced a properly warm period — summers 3 to 5°C hotter than modern Britain, mild winters, dense forest, hippos in the Thames. And the third group were modern wolves from Poland, where temperatures have been climbing steadily by a quarter to four-tenths of a degree per decade over the last 65 years and winter snow cover is in retreat.

The pattern that emerged was stark. Wolves from the warmer interglacial had significantly rougher, more complex tooth surfaces than those from the cooler period — a signature of durophagy, the technical term for crunching through bones and other hard tissue. They were, it seems, consuming carcasses far more thoroughly, gnawing through parts of a kill that wolves in colder times left behind.

Here’s the kicker: modern Polish wolves showed the same dental wear as the ancient warm-climate group. Statistically, their tooth textures were indistinguishable. “The real surprise was that modern wolves from Poland, where climate warming is also ongoing, show the same patterns as those from the younger interglacial,” says Professor Danielle Schreve, Heather Corrie Chair in Environmental Change at Bristol, “highlighting that they are also experiencing hitherto hidden ecological stress.”

Hidden is the operative word. The grey wolf is listed as Least Concern by the IUCN, and — perhaps remarkably — climate change does not even feature among the recognised threats to the species. Wolves are apex predators, adaptable, mobile. They eat everything from deer and wild boar to beaver and berries. We tend to assume they’ll cope. But the DMTA data suggest that warming is quietly forcing wolves into a harder, less efficient way of feeding, one that involves more scavenging and more bone processing, and the ecological cost of that shift is not yet factored into conservation plans.

Why would warmer winters make life tougher for wolves? The logic runs counter to what you might expect. Wolves actually thrive in harsh cold. Deep snow weakens their ungulate prey — deer and boar struggle to reach ground vegetation and can’t flee as quickly through drifts. Wolves, with their long legs and large paws, move more easily on packed snow and ice. Cold winters are associated with heavier wolves and better pup survival. Take the snow away, and that advantage erodes. Prey stays healthier, harder to catch. Hunting becomes more energetically expensive. So wolves compensate: they scavenge more, strip carcasses more completely, crack open bones to get at marrow they’d otherwise ignore.

“The findings suggest wolves were working harder to extract nutrition during warmer climate periods,” Burtt says, “scavenging more extensively or consuming parts of prey they would normally avoid.”

The team’s analysis was thorough. Sixty-two teeth in total, drawn from seven Pleistocene sites across Britain and multiple locations in Poland. They scanned the enamel surfaces with a confocal profiler at extremely high resolution — each scan covering a patch roughly a quarter of a millimetre across — and ran the data through both scale-sensitive fractal analysis and a battery of ISO surface texture parameters. The statistical separation between the warm-period and cool-period wolves was clear and consistent across multiple measures; nineteen texture parameters differed significantly between the two Pleistocene groups alone.

There is, mind you, a wrinkle of cautious optimism in the data. Polish wolves are currently able to offset some of the climate-related dietary stress by hunting deer and wild boar near farmland, where prey congregates around crops and field edges. They also scavenge roadkill — an unintentionally abundant food source in a country with expanding ungulate populations and a lot of traffic. Wolves living close to human landscapes, ironically, may fare better in a warming world than those in remote wilderness. Dr Neil Adams, Curator of Fossil Mammals at the Natural History Museum, points out that the fossil specimens are themselves a kind of resource — teeth that “have been part of the national collection for over 175 years” now being put to work on a thoroughly modern problem.

But the broader implication is less comforting. Not all wolf populations have farmland and motorways to fall back on. Wolves in remote boreal forests or mountain ranges, far from human-modified environments, face the same climatic squeeze without the compensatory food sources. And if the last interglacial — when Britain hosted hippos and the forests were thick with thermophilous trees — serves as any kind of analogue for where we’re heading, then the dietary stress visible in today’s Polish wolves could intensify considerably. Climate change, Burtt argues, should be considered a significant factor in wolf conservation planning going forward. It’s a strange kind of threat — invisible on the outside, written only in the microscopic topography of worn teeth. But it is there, scratched into the enamel, and has been for a very long time.

Study link: Climate change challenges Grey Wolf resilience: Insights from Dental Microwear’