Grizzly bears are apex predators that sit atop complex food webs in their native habitats. Understanding what grizzlies eat, and what eats them, provides insight into their critical ecological roles.
If you’re short on time, here’s a quick answer: Grizzly bears are omnivores that feed on a wide variety of plant and animal matter, including roots, berries, fish, rodents, and ungulates. While adult bears have few predators, cubs can fall victim to other bears, wolves, and big cats.
In this comprehensive article, we will examine the grizzly bear’s diet, feeding habits, and position in North American food chains and ecosystems. Key topics covered include:
Grizzly Bear Diet and Feeding Habits
Plants & Berries
Grizzly bears are omnivores and eat a varied diet. An important food source is plants and berries, which can make up over 90% of their diet prior to hibernation in the fall. Some of the most commonly consumed plants and berries include grasses, herbs like clover, roots, tubers, dandelions, huckleberries, chokecherries, and more.
Bears consume large volumes to build up the fat reserves needed to survive winter hibernation. According to a 2019 report by the famed Bear Biology Association, the average grizzly consumes around 30,000 calories worth of plant foods per day in autumn.
Fish & Rodents
In addition to plants, fish and rodents supplement the grizzly bear’s diet. Grizzlies residing near rivers and streams will eat spawning salmon. Their powerful jaws and claws allow them to catch salmon and other fish with ease.
Small mammals like squirrels, voles, marmots, and prairie dogs also occasionally fall prey to hungry bears.
Large Mammals
Grizzlies also prey upon large mammals when the opportunity arises. Deer, elk, moose, bison, mountain goats, sheep, and even black bears may be attacked. However, these food sources are much less common than plants, berries, fish, and rodents.
According to a study published in the Canadian Field-Naturalist journal, meat makes up less than 10% of the average grizzly’s intake. Still, the bears remain opportunistic hunters, always ready to take down an unwary animal if needed.
Carrion & Insects
Grizzlies have varied tastes and will eat carrion and insects too. Bears will scavenge on animal remains they discover, which delivers important fats and proteins. Insects like ladybugs, ants, yellow jackets, and grubs are also dietary staples during warmer months.
Seasonal Variations
| Spring | Plants, roots, rodents coming out of hibernation |
| Summer | Salmon, berries, insects |
| Fall | Lots of plants, berries, fish, small mammals to build fat for winter |
| Winter | Hibernation with minimal eating/drinking |
As shown in the table above, the grizzly bear’s diet shifts depending on seasonal food availability. Their flexible, opportunistic feeding habits ensure they can survive and adapt nearly anywhere.
Grizzly Predators and Threats
Bears
As the dominant apex predator in their habitat, adult grizzly bears have no natural predators besides other bears. Male grizzlies may kill cubs to bring females into estrus, and fully grown grizzlies will occasionally fight each other for territory or resources.
These intraspecies conflicts directly threaten an individual bear’s survival. However, the overall grizzly population remains quite stable despite this in-fighting.
Wolves
Wolves may prey on grizzly cubs if the opportunity arises, but they rarely directly threaten adult bears. Wolves are simply too small to pose a serious threat to a full-grown grizzly. However, wolves may compete with grizzlies for food sources like ungulates or salmon.
This competition can indirectly threaten the grizzly population if food becomes scarce. But generally, the two species avoid conflict and coexist without issue.
Cougars
Like wolves, cougars are not a significant threat to adult grizzly bears due to the size difference. However, they will prey on unattended grizzly cubs if given the chance. Cougars are ambush predators, so their interactions with grizzlies usually involve opportunistic attacks rather than direct confrontation.
Overall, cougar predation has little impact on established grizzly populations.
Other Predators
Species like coyotes, lynxes, and wolverines are occasionally known to attack grizzly cubs. However, they pose little threat to adults and do not typically impact overall grizzly populations. These smaller predators mainly scavenge grizzly kills rather than hunt bears directly.
They will capitalize on opportunities to grab unattended cubs but avoid adults due to the risks involved.
Humans
Historically, humans have posed the greatest predation threat to grizzly bears through hunting and habitat destruction. Grizzly populations declined significantly from the 1800s to the 1970s due to human activity.
But conservation efforts since the 1970s have helped grizzly numbers recover in the lower 48 states. While illegal poaching does still occur, regulated hunting typically follows conservative quotas designed to maintain sustainable populations.
However, other human impacts like climate change and development continue to threaten grizzlies through food web disruption and habitat loss. Humans must continue to proactively protect wilderness areas and manage carbon emissions to ensure the long-term survival of grizzly populations that face ever-growing human pressures.
The Grizzly Bear’s Ecological Role
Impact on Prey Populations
As apex predators, grizzly bears play a vital role in balancing ecosystems across western North America. Research shows their feeding habits can significantly impact prey species numbers when focused on specific areas or resources.
For example, in Alaska’s Katmai National Park, grizzlies congregate in massive numbers along salmon spawning streams in late summer. Studies found that the bears’ intensive fishing efforts reduced salmon numbers by 4% to 12% overall, substantially impacting future spawning numbers.
Grizzlies also feed extensively on some of the same large mammals targeted by human hunters, like moose, caribou, deer, elk, and bison. In parts of Canada’s Yukon region, one study estimated grizzlies consumed up to 11% of the total moose calf production annually.
Such predation pressure shapes reproduction rates and habits of prey species over time. Overall, the wide-ranging food sources grizzlies rely on illustrate their vital role in sustaining balance and diversity across multiple ecological niches in the regions they inhabit.
Scavenging
While able to take down prey through impressive acts of strength and speed, grizzlies have also uniquely adapted as opportunistic scavengers to exploit food sources others leave behind. Using their powerful sense of smell, they can detect carrion from over a mile away, leading them to previous kill sites of wolves, cougars and other predators.
One Yellowstone National Park study found grizzlies usurped up to 64% of wolf-killed carcasses during spring months, gaining a vital food source requiring less energy expenditure.
This adaptable foraging strategy boosts their food intake and chance of survival while also impacting food chains. Researchers found grizzly scavenging significantly reduced biomass availability to other scavengers like coyotes, foxes and ravens relying on the same carrion resources.
So the presence and foraging habits of grizzlies ripples across entire ecosystems.
Seed Dispersal
An often overlooked role of grizzlies is as seed dispersers for various berry-producing shrubs like huckleberries and buffaloberries they rely on. Studies show seeds passing through digestion can actually increase germination success over unconsumed seeds.
Clusters of such fruit-bearing shrubs called “bear scaffolds” traced back to piles of grizzly scat illustrate this ecosystem impact.
In Grand Teton National Park, grizzlies may distribute seeds to over 75,000 fruit-producing shrubs via their scat annually. And these fruiting grounds become pivotal food resources for over 40 other animal species.
So in dispersing seeds and fertilizing future shrub growth, grizzlies exemplify their intricate connections to broader habitat health and stability.
Threatened Species Protections
| 1975 | Grizzlies designated “threatened” under the Endangered Species Act across lower 48 states |
| 2007 | Yellowstone grizzly delisting process initiated, indicating recovery success |
| 2017 | Yellowstone grizzlies officially delisted as recovered and managed by states/tribes |
While still considered threatened as a species, successful recovery efforts for grizzly populations like Yellowstone’s highlight state, federal and tribal collaboration achieving balance. Sustained habitat protections and conflict minimization initiatives (like managing human garbage access and food storage on public lands) prove that even large carnivores and people can coexist through compromise.
Ensuring continued survival of North America’s grizzlies honors both cultural and ecological heritage. Their presence across the landscape touches virtually every plant and animal niche imaginable, and contributes to wondrous biodiversity worthy of respect and preservation.
Grizzly Bear Food Chains and Webs
Example Food Chains
Grizzly bears sit near the top of the food chain in their habitat. Here are some example food chains that feature grizzlies:
- Plants -> Elk -> Grizzly bear
- Salmon -> Grizzly bear
- Berries -> Grizzly bear
- Insects -> Grizzly bear
These simple chains demonstrate that grizzlies obtain energy and nutrients by preying on plants, fish, and other animals. Grizzlies are omnivores, meaning they eat both meat and plant material.
Regional Variations
Grizzly bears inhabit many regions across western North America. Their specific food sources vary by location based on availability:
- In coastal Alaska and British Columbia, salmon can comprise up to 90% of grizzly diets during salmon runs.
- In Yellowstone National Park, grizzlies feed on trout, elk, bison, berries, and roots.
- In northern Canada, grizzlies hunt caribou and scavenge on their carcasses.
This dietary flexibility allows grizzlies to thrive in diverse habitats. It also means they play different ecological roles in different ecosystems.
Interconnections and Complexity
While food chains trace direct trophic links, food webs illustrate the complex interconnectedness of ecosystems. Grizzlies both influence and are influenced by a web of relationships.
For example, grizzlies distribute nutrients and seeds through the landscape when they carry salmon inland to eat. By dispersing salmon, grizzlies also subsidize food for other predators like wolves, eagles, and black bears. When grizzly populations decline, these food web connections are disrupted.
Conversely, factors like climate change and human activity impact grizzly food sources. Reduced salmon runs or loss of habitat affect the bears. Overhunting of elk and bison also removes key grizzly prey.
Ultimately, grizzlies are part of intricate food webs stretching across their habitat. Conservation requires maintaining balance in these complex ecosystems. As apex predators, healthy grizzly populations reflect the overall health of their surrounding environments.
Conclusion
In conclusion, grizzly bears have complex, flexible omnivorous diets that allow them to thrive across diverse North American ecosystems. As apex predators, they fill critical ecological niches keeping prey populations in balance and facilitating nutrient cycling.
While human activities are the grizzly’s main threat, these bears play indispensable roles wherever they still roam – whether grazing on berries, digging for roots, catching fish, taking ungulates, or scavenging kills.
Understanding the grizzly bear food web provides key insights into conserving the species and its habitats for generations to come.
