Predation on Alces alces by Ursus arctos

By Antoni V Milewski and Anthony J Mills · Originally published 11 July 2026

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My commentary:

Anterior and posterior auricular flagg in Ursus arctos

This individual of U. arctos is adolescent, not adult

Remarkably stupid behaviour on the part of Alces alces

Why did A. alces not simply swim away?

Some attempt at self-defence by means of forehooves, but inept

Some?vocalisation by the victim

Chatgpt

MY QUESTION

Compare the swimming abilities of Alces alces and Ursus arctos, in the context of an adult female of the carnivore pursing an adult female of the herbivore in deep water. Reply in terms of both speed and endurance. Supply full references.

ANSWER FROM CHATGPT

The available evidence suggests that, in deep water, an adult female moose (Alces alces) would generally have the advantage over an adult female brown bear (Ursus arctos) in both sustained swimming speed and endurance, although direct experimental comparisons have never been made.

This conclusion rests on comparative morphology, documented swimming performance, and the ecology of the two species.

Swimming speed

The best documented quantitative data are for moose.

Moose are highly aquatic cervids. They routinely cross large lakes and rivers, forage on submerged aquatic vegetation, and migrate by swimming. Numerous zoological sources report that they can maintain swimming speeds of about 9–10 km h⁻¹ (5.5–6 mph) and may swim up to 20 km without leaving the water.

By contrast, brown bears are competent swimmers, but they are primarily terrestrial. Quantitative measurements of swimming speed in Ursus arctos are scarce. Observational studies describe them as capable of crossing broad rivers, lakes, and coastal channels, but they are not known for prolonged, rapid aquatic travel. Unlike polar bears, whose locomotor system is much more specialized for aquatic movement, brown bears lack any obvious anatomical specialization for efficient swimming.

Consequently, the available evidence indicates that

Moose: sustained swimming ≈9–10 km h⁻¹.

Brown bear: probably somewhat slower during prolonged swimming; no published evidence demonstrates sustained speeds exceeding those of moose.

Endurance

The difference is even clearer regarding endurance.

Moose regularly perform long-distance swims as part of normal behaviour.

They

• feed extensively on aquatic macrophytes,

• routinely swim between islands,

• cross large lakes,

• may remain in water for extended periods while foraging.

Their elongated body, high buoyancy produced by enormous lungs, and long legs permit efficient propulsion with relatively little energy expenditure.

Brown bears certainly possess considerable endurance in water. Individuals have been documented swimming several kilometres across lakes or marine channels, and coastal populations regularly swim between islands. However, such swims are comparatively infrequent and are not a routine component of daily feeding ecology.

Thus, the available evidence favours substantially greater endurance in moose.

Predator–prey implications

There is an important ecological observation.

Although brown bears do prey on adult female moose, documented attacks almost always begin on land, where the bear can exploit acceleration, surprise, and the moose’s reduced manoeuvrability in dense vegetation. Adult female moose are vulnerable chiefly when accompanied by calves or when otherwise disadvantaged.

I am unaware of any published account describing a brown bear deliberately pursuing an adult moose through deep open water over a prolonged distance.

Indeed, water is often regarded as a relative refuge for moose because

• they are highly adapted to aquatic locomotion,

• they can maintain steady swimming for long distances,

• bears lose much of their terrestrial speed advantage once forced to swim.

Overall assessment

Characteristic Alces alces Ursus arctos

Sustained swimming speed Higher (≈9–10 km h⁻¹ documented) Probably lower; few quantitative data

Swimming endurance Very high; swims up to ~20 km documented High, but generally less than moose

Aquatic specialization Strong; routine aquatic feeding and travel Moderate; swimming mainly for crossing water

Likely outcome of pursuit in deep water Likely to maintain or increase distance from an adult female bear Unlikely to overtake a healthy adult female moose solely by swimming

Accordingly, if an adult female brown bear began pursuing a healthy adult female moose in deep open water, the balance of available evidence indicates that the moose would usually be expected to pull away gradually through superior sustained speed and especially superior endurance, assuming neither animal was impeded by shoreline, floating ice, current, or exhaustion.

References

• Ballard, W. B. 1992. Bear predation on moose: a review of recent North American studies and their management implications. Alces Supplement 1: 162–176.

• Dahle, B., Wallin, K., Cederlund, G., Persson, I.-L., Selvaag, L. S. & Swenson, J. E. 2013. Predation on adult moose (Alces alces) by European brown bears (Ursus arctos). Wildlife Biology 19: 165–169..

• Franzmann, A. W. & Schwartz, C. C. (eds.). 1998. Ecology and Management of the North American Moose. Smithsonian Institution Press, Washington, D.C.

• Geist, V. 1998. Deer of the World: Their Evolution, Behaviour, and Ecology. Stackpole Books, Mechanicsburg, Pennsylvania.

• Peterson, R. L. 1955. North American Moose. University of Toronto Press, Toronto.

• Telfer, E. S. 1984. Circumpolar distribution and habitat requirements of moose (Alces alces). In Olson, R., Hastings, R. & Geddes, F. (eds.), Northern Ecology and Resource Management, University of Alberta Press, Edmonton, pp. 145–182.

• Animal Diversity Web. Alces alces account (summarizing primary literature on locomotion and swimming performance).

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Chatgpt

MY QUESTION

Which authors have described predation on healthy adult individuals of Alces alces by Ursus arctos? Supply full references.

ANSWER FROM CHATGPT

Yes. Although brown bears most commonly prey on moose calves, a number of authors have documented or reviewed predation on healthy adult Alces alces by Ursus arctos. The strongest evidence comes from telemetry studies in Alaska and Scandinavia.

The principal authors are as follows.

Bjørn Dahle, Kjell Wallin, Göran Cederlund, Inga-Lill Persson, Line Stabell Selvaag & Jon E. Swenson (2013)

This is the first detailed European study devoted specifically to adult moose predation by brown bears. The authors documented successful predation by Scandinavian brown bears on free-ranging adult moose in south-central Sweden. They concluded that healthy adult females were occasionally killed, although at a much lower rate than reported from many North American populations. Successful attacks were made only by adult bears, particularly adult males.

Reference

Dahle, B., Wallin, K., Cederlund, G., Persson, I.-L., Selvaag, L. S. & Swenson, J. E. (2013). Predation on adult moose Alces alces by European brown bears Ursus arctos. Wildlife Biology, 19(2), 165–169.

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Warren B. Ballard

Ballard reviewed numerous Alaskan studies and emphasized that grizzly bears are capable of killing not only calves but also healthy adult moose. He summarized kill rates and concluded that brown bears can be significant predators of adult moose in some ecosystems.

Reference

Ballard, W. B. (1992). Bear predation on moose: A review of recent North American studies and their management implications. Alces Supplement, 1, 162–176.

Warren B. Ballard & Victor Van Ballenberghe

Their review chapter synthesized evidence from Alaska showing that adult grizzly bears regularly kill adult moose where the species coexist, particularly during spring.

Reference

Ballard, W. B. & Van Ballenberghe, V. (1998). Predation on moose. In A. W. Franzmann & C. C. Schwartz (eds.), Ecology and Management of the North American Moose. Smithsonian Institution Press, Washington, D.C., pp. 247–273.

Robert O. Stephenson and colleagues

One of the classic Alaskan telemetry studies demonstrated that grizzly bears killed adult cows as well as calves. The paper was influential because it documented predation rather than scavenging through field investigations.

Reference

Stephenson, R. O., Van Ballenberghe, V., Goodwin, E. & Hughes, J. H. (1987). Interactions of wolves, grizzly bears, and moose in southcentral Alaska. In Proceedings of the Second North American Moose Conference and Workshop, 1987.

Victor Van Ballenberghe and co-workers

Throughout a series of studies in Alaska, Van Ballenberghe documented that grizzly bears occasionally kill prime-aged adult moose, although calves comprise the majority of kills.

One important reference is:

Van Ballenberghe, V. & Ballard, W. B. (1994). Limitation and regulation of moose populations: the role of predation. Canadian Journal of Zoology, 72, 2071–2077.

Boertje and colleagues

Studies in interior Alaska showed that brown bears kill both calves and adults and that adult predation may contribute appreciably to annual mortality in some populations.

Representative reference:

Boertje, R. D., Keech, M. A., Young, D. D., Kellie, K. A. & Dale, B. W. (2010). Managing for elevated yield of moose in interior Alaska. Journal of Wildlife Management, 74, 314–327.

Were the adults healthy?

This is an important distinction.

The Scandinavian paper by Dahle et al. (2013) explicitly investigated predation rather than scavenging. Most adult victims were not senescent animals, and several were apparently healthy adult cows. The authors concluded that Scandinavian brown bears are capable of killing healthy adult moose, albeit infrequently.

Similarly, the Alaskan literature reviewed by Ballard (1992) and Ballard & Van Ballenberghe (1998) indicates that grizzly bears can and do kill healthy adult moose, especially in spring when snow conditions favour bears or when adult males attack solitary cows. The frequency is much lower than for calves, but the phenomenon is well established.

Overall, the best-supported authorities documenting predation on healthy adult Alces alces by Ursus arctos are Ballard, Van Ballenberghe, Boertje, and, for Europe, Dahle and colleagues, with Dahle et al. (2013) being the definitive dedicated study on the subject.

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Posted on July 12, 2026 01:10 AM by
milewski

The author added the following in comments beneath the original post.

Chatgpt

MY QUESTION

When Alces alces is attacked by predators, is it known to vocalise loudly in distress? Supply full references.

ANSWER FROM CHATGPT

The short answer is no. Unlike many cervids, adult moose (Alces alces) are not known for producing loud distress vocalisations when attacked by predators. Their primary anti-predator strategy is physical defence (standing their ground, kicking with the forelegs, stamping, or fleeing), rather than conspicuous vocal signalling. The scientific literature contains remarkably few documented observations of loud distress calls by adults during predation events.

There are, however, some important distinctions.

Adults

The standard accounts of moose behaviour describe a relatively limited vocal repertoire. Vocalisations are used principally during the rut and in communication between cows and calves, not as alarm or distress calls directed at predators.

Modern bioacoustic work likewise recognises only a small repertoire consisting mainly of:

rutting moans of cows,

grunts of bulls,

occasional roars or threat vocalisations,

calf calls.

The study does not identify a stereotyped loud distress call associated with predation.

Similarly, reviews of anti-predator behaviour in moose emphasise:

increased vigilance,

flight,

aggressive defence,

responses to predator sounds,

rather than vocal alarm or distress.

Calves

Moose calves are different.

Calves give contact calls to their mothers and may vocalise vigorously when separated or threatened. These calls probably function to maintain maternal contact and may become distress calls when the calf is attacked. This behaviour is familiar to wildlife biologists, although detailed quantitative studies during actual predator attacks are scarce.

Comparison with other deer

This is noteworthy because several other cervids are much more vocal under attack. For example:

Cervus canadensis calves commonly scream when seized by predators.

Odocoileus virginianus often emit loud distress bleats.

Capreolus capreolus may produce loud distress cries when captured.

Comparable reports for adult Alces alces are exceptionally uncommon.

Why?

Moose are largely solitary animals. In social mammals, distress calls often recruit relatives or group members or confuse predators. Moose usually lack nearby conspecifics able to assist, so natural selection may favour silent escape or physical defence rather than conspicuous vocalisation. This interpretation is consistent with general theories of distress calling in mammals.

Conclusion

Current evidence indicates that adult Alces alces do not have a reputation for vocalising loudly in distress when attacked by predators. While isolated anecdotal reports exist of vocalisations during dangerous encounters, these are not recognised as a characteristic component of the species’ anti-predator behaviour. Calves, however, may vocalise loudly when threatened or separated from their mothers.

References

Bhardwaj, M., Lodnert, D., Olsson, M., Winsvold, A., Eilertsen, S. M., Kjellander, P., & Seiler, A. (2022). Inducing fear using acoustic stimuli—A behavioral experiment on moose (Alces alces) in Sweden. Ecology and Evolution, 12, e9492..

CitedDOI

Franzmann, A. W., & Schwartz, C. C. (Eds.). (1998). Ecology and Management of the North American Moose. Smithsonian Institution Press, Washington, D.C.

Geist, V. (1998). Deer of the World: Their Evolution, Behaviour, and Ecology. Stackpole Books, Mechanicsburg, Pennsylvania.

Klump, G. M., & Shalter, M. D. (1984). Acoustic behaviour of birds and mammals in the predator context. Zeitschrift für Tierpsychologie, 66, 189–226.

Zager, A., Ahlberg, S., Boyan, O., Brierley, J., Eddington, V., Moll, R. N., & Kloepper, L. N. (2024). Characteristics of wild moose (Alces alces) vocalizations. JASA Express Letters, 4(4), 041201..

CitedDOI

Animal Diversity Web. Alces alces account (communication section).

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Chatgpt

MY QUESTION

Does Ursus arctos possess conspicuously pale pelage on the ear pinnae, and if so which author has described this as a functional aspect of adaptive colouration? Supply full references.

ANSWER FROM CHATGPT

Yes, brown bears (Ursus arctos) often possess noticeably paler hair on the ear pinnae, particularly on the margins and posterior surfaces of the ears. This feature is familiar to field mammalogists and wildlife artists, although its conspicuousness varies among subspecies and colour morphs. However, I have found no author who has specifically proposed that the pale ear pinnae themselves constitute an adaptive colour pattern with a demonstrated function (e.g. disruptive coloration, communication, or predator deception).

The evidence divides into two parts.

Description of pale ear pinnae

General descriptions of Ursus arctos acknowledge that the head and shoulders are commonly paler than the rest of the body, and photographs in standard monographs frequently show ears edged or clothed in pale buff or grey hairs.

For example:

Pasitschniak-Arts (1993) described the species as varying from pale tan to almost black, noting that “generally, head and shoulders are paler,” consistent with the commonly observed pale ears.

Likewise, regional faunas such as Hall (1981), Brown (1985) and Murie (1985), cited in Pasitschniak-Arts’ review, depict or describe bears whose rounded ears are noticeably lighter than the surrounding head fur.

Has anyone interpreted the pale ears as adaptive coloration?

I could not locate any primary source that attributes a specific adaptive function to the pale ear pinnae of Ursus arctos.

This absence is notable because the classic literature on adaptive coloration is extraordinarily comprehensive.

The principal works are:

Adaptive Coloration in Animals

Concealing-Coloration in the Animal Kingdom

Cott discussed numerous mammalian markings—eye patches, tail tips, countershading, disruptive markings, and facial patterns—but did not single out the pale ears of brown bears as possessing a signalling or cryptic function.

Similarly, Ortolani’s comparative analysis of colour patterns in Carnivora examined spots, stripes, eye markings and tail markings as potential adaptive structures, but did not include ear-pinna coloration among the characters analysed.

Interpretation

At present, the pale ear pinnae appear to be regarded simply as one element of the highly variable pelage of Ursus arctos. They may arise because the hairs of the head are generally lighter than those elsewhere on the body, rather than because the ears themselves have been subject to independent selection.

This does not mean the feature lacks function. Plausible hypotheses include:

reducing the visual prominence of the ears by blending them with the paler head,

disrupting the outline of the head,

or functioning in close-range visual communication.

However, these remain hypotheses. I found no published author who has explicitly argued for any of these explanations in brown bears.

References

Brown, G. 1985. The Great Bear Almanac. Lyons & Burford, New York.

Cott, H. B. 1940. Adaptive Coloration in Animals. Methuen, London.

Hall, E. R. 1981. The Mammals of North America. 2nd ed. John Wiley & Sons, New York.

Murie, O. J. 1985. A Field Guide to Animal Tracks. 2nd ed. Houghton Mifflin, Boston.

Ortolani, A. 1999. Spots, stripes, tail tips and dark eyes: predicting the function of carnivore colour patterns using the comparative method. Biological Journal of the Linnean Society 67: 433–476.

Pasitschniak-Arts, M. 1993. Ursus arctos. Mammalian Species 439: 1–10.

Thayer, G. H. 1909. Concealing-Coloration in the Animal Kingdom. Macmillan, New York.

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Thanks for the tip, but so far I have failed in my attempts to instal Claude.

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