Brown bears move where their food grows

The brown bear, Ursus arctos, is often described as adaptable, and its European range has never stayed still for long.

New research shows that the bear’s wanderings are tied less to temperature than to where its food grows or grazes – an important detail with big conservation consequences.

Pablo M. Lucas and colleagues at the University of Seville analyzed more than three million bear locations and the energy yield of 276 food species to find the pattern.

Bears follow food with most energy

“We detected 276 species in their diet. Bears occupy those places where the most energy from the species in their diet is available,” explained Lucas.

Brown bears consume anything from acorns to red deer, shifting diet with local supply. Lucas’s team confirms that bears settle where the most calories are packed into the landscape, a principle ecologists call trophic energy optimization. 

Europe holds about 17,000 free‑ranging brown bears spread over 22 countries, yet the population is fragmented into 14 sub‑populations, from the Cantabrian Mountains to Karelia.

The IUCN classifies the species as “Least Concern” globally, but several regional groups remain vulnerable. Fragmentation matters because food landscapes vary sharply across short distances.

Climate shifts food sources for bears

Climate change is already nudging thousands of species poleward and uphill, some three times faster than biologists once estimated. As fruiting plants, insects and ungulates relocate, bears face a moving target. 

In warmer regions such as Greece and Türkiye, the study found bears behaving almost like herbivores, with nuts and berries dominating the diet.

Farther north in Scandinavia and Finland, meat from wild boar or moose supplies over half of a bear’s annual calories.

American grizzlies offer a parallel: on Alaska’s Kodiak Island, warmer summers now ripen elderberries during salmon runs, and many bears abandon fish for fruit.

The European analysis suggests similar switches are likely whenever plant and animal phenology collide.

Mapping the energy landscape

To quantify edible energy, the team combined scat and stomach studies with remote‑sensing models of plant and prey habitat.

A key variable was isothermality, the ratio of day‑to‑night temperature range to annual range, which influences plant productivity.

Areas rich in reproductive plants such as oak and beech mast scored high for bears in Spain, while regions with dense roe‑deer populations pulled bears east of the Carpathians.

The researchers then layered these food maps onto climate and land‑use projections for 2050. Where forests shrink or heat stress pushes oaks uphill, the calories disappear and the bear’s probability of presence drops with them.

Bear food zones may shrink

Under a mid‑range emissions pathway, suitable bear habitat could contract by one‑third if both abiotic (climate, land use) and biotic (food availability) changes unfold as forecast.

Losses are steepest in the East Balkan and Türkiye groups, where warming outpaces plant adaptation. In contrast, the Scandinavian and Karelian sub‑populations may gain ground as forests march north, provided prey species keep pace.

A separate Swedish analysis of 527 bear scats showed similar north-south dietary splits and underlines that bears quickly alter foraging tactics when new options arise.

Such flexibility could buffer northern bears but offers little help to isolated southern populations hemmed in by farmland and roads.

Implications for people and policy

Europe’s large carnivores have rebounded over the past two decades, sparking new debates about coexistence. Where wild prey declines, bears turn to orchards, beehives and livestock carcasses, raising conflict costs.

Predicting hotspots of future food scarcity can guide compensation schemes and habitat corridors before tensions flare.

Forest managers also gain a roadmap: protecting seed‑producing trees in southern Europe may retain critical autumn fattening grounds, while maintaining continuous ungulate habitat in the north ensures carnivorous diets stay wild.

The study argues that conservation targets should shift from static range maps to dynamic “energy maps” that track how calories, not just climate, flow across the continent.

Not all species adapt like bears

Brown bears are generalists, able to switch food sources as the landscape changes. But many species aren’t so lucky.

Animals with a specialist diet, such as the Iberian lynx or alpine butterflies, may not adapt as quickly if their primary food vanishes or migrates beyond reach.

Species with limited mobility or narrow climate tolerance face a double threat: they can’t chase food, and even if they could, suitable shelter might not be there.

Conservation strategies that work for flexible foragers like bears won’t always translate to more fragile species caught in tight ecological niches.

Next step is testing other predators

Lucas and co‑authors hope to expand the model to wolves and lynx, testing whether prey‑driven range forecasts improve planning for multiple predators at once.

The researchers are also calling for finer‑scale monitoring of plant phenology so managers can spot mismatches early.

For now, the brown bear reminds us that protecting a species means protecting its pantry. Where acorns fall and deer graze today will shape where cubs are born tomorrow.

The study is published in the journal Global Change Biology.

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