SHORT COMMUNICATION

Cannibalism in bears
Maximilian L. Allen1,7 , Miha Krofel2 ,Koji Yamazaki3 , Emmarie P. Alexander4 , andShinsuke Koike5,6

Key words: bear, behavior, cannibalism, foraging ecology, infanticide, mortality, nutritional ecology, predation, scavenging, sexually selected infanticide
DOI: 10.2192/URSUS-D-20-00031.2
Ursus 33:article e10 (2022)

1

Illinois Natural History Survey, University of Illinois,
1816 S Oak Street, Champaign, IL 61820, USA
2
Department of Forestry, Biotechnical Faculty, Universityof Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana,
Slovenia
3
Department of Forest Science, Tokyo University ofAgriculture, Setagaya, Tokyo, Japan
4
Department of Animal Sciences, University of Illinois at
Urbana-Champaign, Urbana, IL 61801, USA
5
Institute of Global Innovation Research, Tokyo
University of Agriculture and Technology, Fuchu, Japan
6
Institute of Agriculture, Tokyo University of Agriculture
and Technology, Fuchu, Japan

Cannibalism, where an animal consumes a conspecific individual, is found throughout the animal kingdom(Allen et al. 2020, Gómez et al. 2021). It is primarily believed to increase fitness (i.e., consuming provides nutrition, whereas killing reduces immediate and future competition for food and other resources; Gómez et al. 2021).
However, consumption of conspecifics can come with acost in a form of parasite transmission, which is the reason that carnivores generally avoid consuming the carcasses of other carnivores, especially their own species(Moleón et al. 2017). There can be many reasons andmotivations for instances of cannibalism, and these canvary by species and season (Allen et al. 2020, Gómez et al.
2021). It is therefore important to understand the different
types of cannibalism and why they occur among different
species.
Cannibalism tends to be associated with 1 of 5 forms(Table 1; Allen et al. 2020). The first distinction is to separate the consumption of a conspecific that was killed by
the individual consuming it (predation) from consumption of a conspecific that died of another cause (scavenging). For cannibalism resulting from predation, we distinguish among several types that vary in respect to the age
and relatedness of the consumer and victim: conspecificstrife (killing of an adult), siblicide (killing of a sibling),
filicide (killing of one’s dependent young), and (nonfamilial) infanticide (full definitions provided in Table 1).
Conspecific strife is the only type of predation-caused
cannibalism involving adults as a victim but is typicallyless common than other types of cannibalism, potentiallyas a result of the difficulty and risks associated with killinga competitor that is similar in size and strength (Gómez
et al. 2021). In most predators, intraspecific predation
is more commonly focused on dependent young, which
are easier to kill than adults. Killing of nonrelated young(i.e., nonfamilial infanticide) is typically one of the mostcommon forms of cannibalism, allowing an individual
to both feed on a young animal as a resource and also
reduce future competition for resources for the individual and their progeny (Hrdy 1979). In some groups, suchas raptors, siblicide (the killing and eating of siblings)
and filicide (the killing and eating of dependent young by

Abstract: Bears are the largest terrestrial carnivores, andmost bear species can be characterized as opportunistic omnivores. An infrequent foraging tactic for bears iscannibalism, where a bear consumes a conspecific individual, either through scavenging or following intraspecific predation. Although several reports of cannibalism
events are known, no attempt has been made so far togather the available information to analyze for general
patterns. We therefore performed a systematic literature
review to understand patterns of cannibalism in bears. We
documented 39 studies detailing 198 cannibalism events.
We only found evidence of cannibalism in 4 of the 8
bear species, with more events reported for polar bears(Ursus maritimus; n = 107, 54.0%) than for all otherspecies combined. Cannibalism was most frequently associated with infanticide (n = 66, 33.3%) and conspecific strife (n = 30, 15.2%), both of which were more
frequent among males than females. The most common
apparent reason for cannibalism among predators is toincrease fitness (i.e., eating a conspecific increases nutrition, whereas killing reduces competition for resources),but is also often linked to sexually selected infanticide
in bears. Cannibalism most often appears to be an opportunistic consumption of an available carcass and not
directly connected with the primary cause of death. As
such, cannibalism in bears may be more casual and opportunistic than a behavior that evolved as a life history
strategy.

7

email: maxallen@illinois.edu

12 SHORT COMMUNICATION
Table 1. Categorization and definitions for types of cannibalism, with respect to the mortality cause.
Type of cannibalism

Source of the carcass

Definition

Scavenging

Scavenging

Conspecific strife
Siblicide
Filicide(Nonfamilial) infanticide

Predation
Predation
Predation
Predation

Consumption of a conspecific that died of other causes (i.e., not killed by theindividual consuming it).
The killing and eating of an adult conspecific.
The killing and eating of sibling(s), usually while dependent young.
The killing and eating of dependent young by parents.
The killing and eating of unrelated dependent young by conspecifics.

parents) can be common and often revolves around broodsuccess, with the weaker individuals being killed and fed
upon to increase the survival of siblings, especially inyears with lower food availability (Bechard 1983, Allenet al. 2020).
Cannibalism has been observed many times in bears,
but it is an infrequent foraging tactic and the reasonsfor cannibalism are unclear. Most bear species are opportunistic omnivores that forage on a variety of foodsources, including carrion (Mattson 1997, Narita et al.
2006, Bojarska and Selva 2012). Bears are also known to
be one of the most effective terrestrial scavengers (Krofel et al. 2012, Inagaki et al. 2020) and therefore it is
not surprising that they also consume dead conspecifics
found while foraging, despite the risk of disease or parasite transmission. Beside scavenging, some bear species,
most notably the polar bear (Ursus maritimus), are also
known as effective predators capable of subduing large
prey (Derocher et al. 2000, 2002; Ordiz et al. 2020).
These characteristics also give them the ability to killconspecifics, especially when they are smaller than theattacker. However, not all intraspecific killing results in
consumption of the victim, suggesting that motivationsfor killing are not always connected with obtaining offood. Among the most commonly cited reasons for intraspecific killing among bears is sexually selected infanticide, where male bears kill (and sometimes consume)
cubs that are not their own in order to increase mating opportunities (Hrdy 1979, Swenson et al. 1997, Bellemain
et al. 2006). Sexually selected infanticide is a frequent behavior in bears that has led to behavioral adaptations andoften has direct effects on populations (Swenson et al.
1997, Miller et al. 2003, Swenson 2003, Steyaert et al.
2013).
To understand the frequency and patterns of cannibalism by bears, we performed a systematic review of peerreviewed scientific literature. Our aims were to document
instances of cannibalism in bears and search for patterns,
including the prevalence of different types of cannibalism
and their frequency among different species and regions.

We also identified the most pressing knowledge gaps andprovide guidelines on how to collect data when a potential
intraspecific predation event or cannibalism is detected in
the field.

Literature review
On 10 March 2021, we performed a systematic literature search to determine the frequency of documentationof cannibalism among bears. We searched Web of Science for the terms “cannibal*”, “infanticide”, and “mortality” matched with the search terms “Ursus” and “bear”
in both English and Japanese. We then read each entry
and removed duplicate reports and mismatched publications, as well as those not from peer-reviewed journals andstudies involving captive animals. We augmented our systematic review of the literature using snowball sampling(searching the references of papers we reviewed for additional documentations). In summarizing the results ofour review, we considered either studies (entire publications) or events (individual reports of cannibalism withinpublications).

Results
We documented 39 studies detailing 198 cannibalism
events. Cannibalism was most frequently associated with
infanticide (n = 66, 33.3%), conspecific strife (n = 30,
15.2%), and scavenging (n = 26, 13.1%; Table 2). Eventsof filicide (n = 8, 4.0%) were less frequently associatedwith cannibalism and we did not record any publications
or events that reported siblicide (Table 2). There werealso 68 events of cannibalism, comprising 34.3% of all
events, where it was not possible to determine the type(labeled “Undetermined*” in Table 2 and Fig. 1b), 64 ofwhich came from scat studies where it was impossible
to determine the origin of the bear remains found in thescat.
Reports included cannibalism in 4 of the 8 bear species,
including polar bear (nstudies = 15, nevents = 107, 54.0%),
Ursus 33:article e10 (2022)

ALLEN ET AL.

3

Table 2. A literature review of 5 types of cannibalism by bears. The review includes bear species, location,
number and type of cannibalism, sex of cannibals, and the study.
SpeciesAmerican black bear
American black bear
American black bear
American black bear
Asiatic black bear
Asiatic black bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
American black bear
Polar bear
Polar bear
Polar bear
American black bear
American black bear
American black bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Brown bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
Polar bear
American black bear
American black bear

Location
AB, Canada
BC, Canada
FL, USAFL, USAJapan
Russia Far East
AK, USAAK, USA
Cantabrian Mountains,
Spain
GreeceKodiak, AK, USA
Scandinavia
Trentino, Italy
AK, USA
Beaufort Sea
MB, Canada
NT, Canada
Novaya Zemlya,
RussiaSouthampton Island,
NU, Canada
Svalbard, Norway
MA, USA
Svalbard, Norway
Wrangel Island, Russia
Wrangel Island, Russia
AZ, USABC, Canada
PA, USAAK, USAAK, USAAK, USA
Cantabrian Mountains,
Spain
Kodiak, AK, USA
SwedenTrentino, Italy
WY, USAAK, USA
Churchill, MB, Canada
Franz Josef Land,
RussiaFranz Josef Land,
RussiaFranz Josef Land,
RussiaMB, Canada
Novaya Zemlya,
RussiaSvalbard, Norway
Svalbard, Norway
Svalbard, Norway
Svalbard, Norway
AB, Canada
UT, USA

Ursus 33:article e10 (2022)

Cannibalism
eventsType ofcannibalism

Sex of cannibal

Study

2
3
1
2
1
1
1
1
1

Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife

Male
Male
Female with cubs
MaleFemaleMale
Male
FemaleMale

Tietje et al. 1986
Davis and Harestad 1996
Garrison et al. 2007
Garrison et al. 2007
Allen et al. 2021
Kolchin 2019
Dean et al. 1986
Hessing and Aummiler 1994
Ballesteros et al. 2021

1
1
2, 1
1
2
1
1
1, 1
2

Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife
Conspecific strife

Male
FemaleMale, female
Male
Male
Male
Male
Male, unknown
Male

Karamanlidis et al. 2015
Troyer and Hensel 1962
Swenson et al. 2001
Davoli et al. 2018
Amstrup et al. 2006
Stirling et al. 2008
Jonkel 1970
Taylor et al. 1985
Ivanov et al. 2020

1

Conspecific strife

Male

Lunn and Stenhouse 1985

2
2
3
1
2
3
3
1
1
2, 1, 1

Conspecific strife
Filicide
Filicide
Filicide
Filicide
Infanticide
Infanticide
Infanticide
Infanticide
Infanticide

Stirling and Ross 2011
Elowe and Dodge 1989
Taylor et al. 1985
Belikov and Kuprijanov 1977
Uspenski and Kistchinski 1972
LeCount 1987
Davis and Harestad 1996
Alt and Gruttadauria 1984
Dean et al. 1986
Hessing and Aummiler 1994

2
6

Infanticide
Infanticide

Male
FemaleFemaleFemaleFemaleMale
Male
Unknown
Male
Female, male,unknown
Male
Male

2, 1
2
1
1
1
1
2

Infanticide
Infanticide
Infanticide
Infanticide
Infanticide
Infanticide
InfanticideMale, unknown
Male
Male
Male
Male
Male
Male

Troyer and Hensel 1962
Bellemain et al. 2005
Davoli et al. 2018
Mattson et al. 1992
Amstrup et al. 2006
Dyck and Daley 2002Nansen 1897

1

Infanticide

Male

Parovshchikov 1964

1

Infanticide

Unknown

Ivanov et al. 2020

1
2

Infanticide
Infanticide

Male
Male

Jonkel 1970
Ivanov et al. 2020

2
1
1
26
1
3

Infanticide
Infanticide
Infanticide
Infanticide
Scavenging
Scavenging

Male
Male
Male
Male
Male
Unknown

Derocher and Wiig 1999
Stirling and Ross 2011
Stone and Derocher 2007
Taylor et al. 1985
Tietje et al. 1986
Miller et al. 2017

Olson 1993
Ballesteros et al. 2021

4 SHORT COMMUNICATION
Table 2. Continued
Species

Location

Brown bear
Polar bear
Polar bear

AK, USA
Churchill, MB, Canada
Franz Josef Land,
RussiaNT, Canada
Novaya Zemlya,
RussiaVize Island, Russia
MT, USAWA, USAFL, USAON, Canada
Iwate Prefecture,Japan
Toyama Prefecture,Japan
WY, USA
Hudson Bay, Canada

Polar bear
Polar bear
Polar bear
American black bear
American black bear
American black bear
American black bear
Asiatic black bear
Asiatic black bear
Brown bear
Polar bear

Cannibalism
eventsType ofcannibalism

Sex of cannibal

Study

2, 1
1
1

Scavenging
Scavenging
Scavenging

Female, unknown
Male
Male

Hessing and Aummiler 1994
Dyck and Daley 2002Nansen 1897

78, 1

Scavenging
Scavenging

Unknown
Unknown, Male

Taylor et al. 1985
Ivanov et al. 2020

1
1
1
1
18
1

Scavenging
Undetermined*
Undetermined*
Undetermined*
Undetermined*
Undetermined*

Male
Unknown
Unknown
Unknown
Unknown
Unknown

Ivanov et al. 2020
Jonkel and Cowan 1971
Lindzey and Meslow 1977
Garrison et al. 2007
Obbard and Howe 2008
Sakamoto and Aoi 20062

Undetermined*

Male

Arimoto et al. 20111232

Undetermined*
Undetermined*

Unknown
Unknown

Mattson et al. 1992
Gormezano and Rockwell2013

Fig. 1. Summary of cannibalism among bears, including (a) the type of cannibalism among 4 species:
American black bear (Ursus americanus), Asiatic
black bear (U. thibeticus), brown bear (U. arctos), or
polar bear (U. maritimus); and (b) the type of cannibalism by sex of the bear. Undetermined* indicates
incidents where it was not possible to determine typeof cannibalism.

brown bear (Ursus arctos; nstudies = 10, nevents = 44,
22.2%), American black bear (U. americanus; nstudies =10, nevents = 42, 21.2%), and Asiatic black bear (U. thibeticus; nstudies = 4, nevents = 5, 2.5%). Most events by polar
bears and brown bears were infanticide (npolar = 39, nbrown= 20; Fig. 1a). Most events by American black bears
were conspecific strife (n = 8) or infanticide (namerican =7). All cannibalism events with a known cause for Asiatic black bears were conspecific strife (n = 2). There
were also a large number of undetermined events for eachspecies recorded (npolar = 32, nbrown = 12, namerican = 21,
nasiatic = 3).
Males more frequently showed cannibalism associatedwith infanticide (nmale = 60, nfemale = 4) and conspecificstrife (nmale = 24, nfemale = 5) than did females, but scavenging was more equal among sexes (nmale = 5, nfemale =2; Fig. 1b). All events associated with infanticide by polar
bears (n = 38) and American black bears (n = 6) wereby males. The exception to this pattern was brown bears,
which had 2 reported infanticide events by females, compared with 16 events for males. Brown bears were also
the exception for cannibalism associated with conspecificstrife, with 3 events by females and 6 events by males.
In comparison, all 10 conspecific strife events by polar
bears and 7 of 8 events by American black bears were bymales.
The first study of cannibalism in bears was publishedin 1897 (3 events; Nansen 1897), but then there was a gap
in publications until the 1960s when 2 studies (5 events)
Ursus 33:article e10 (2022)

ALLEN ET AL.
of cannibalism were published. Most decades since had
between 5 and 7 studies published (1970s = 5, 1980s = 7,
1990s = 5, 2000s = 9, 2010s = 7), with varying numberof events reported (1970s = 7, 1980s = 50, 1990s = 31,
2000s = 35, 2010s = 44). Publications of cannibalism
by bears among continents varied greatly, with 23 studies(123 events) in North America, 12 studies (69 events) inEurope, and 5 studies (6 events) in Asia.

Discussion
Our review of cannibalism in bears showed that cannibalism takes multiple forms, each with its own potential evolutionary drivers. Although cannibalism among
predators is generally believed to increase fitness (by increasing nutrition while simultaneously reducing competition for resources; Gómez et al. 2021), in bears it
often appears to be an opportunistic consumption of anavailable bear carcass (via scavenging) or is not directly
connected with the primary cause of death (although cannibalism often follows the intraspecific killing via infanticide, filicide, or conspecific strife). This appears to
be most clearly exhibited by sexually selected infanticide, where male bears and other carnivores kill unrelated dependent young to increase mating opportunities(Swenson et al. 1997, Miller et al. 2003, Bellemain et al.
2006), and the consumption of cubs as food is not the
primary reason for the infanticide. We found no documented cases of siblicide (where one sibling kills another) in bears, although it is relatively common in someother animals (particularly raptors; Allen et al. 2020).
Our review showed that cannibalism is relatively common
among bears, but much less frequent than other types of
predation or foraging behavior. Our review leaves manyquestions unanswered and highlights the need for further
research with emphasis on hypothesis-driven research tounderstand the reasons for the different types of cannibalism in bears.
Likely differences in available resources or behaviors
among species cause different motivations for cannibalism among bears, but it is also primarily a male behavior. Most documented cannibalism events were by polar
bears, perhaps because polar bears are easier to observe
over the long time periods necessary to document predation events. But polar bears are also the most carnivorousand predatory of bears (Derocher et al. 2000, 2002;
Ordiz et al. 2020), and may be more likely to view young
conspecifics as a food source. The high frequency of infanticide by polar bears is often explained by evolutionary reasons, such as sexually selected infanticide, as inother bear species (e.g., Swenson et al. 1997, Miller et al.
Ursus 33:article e10 (2022)

5

2003, Bellemain et al. 2006). However, studies have also
highlighted that male polar bears use young as a foodsource, while also reducing competition for limited resources (Derocher and Wiig 1999). This is important because cannibalism may increase if there is increased fooddeprivation due to future climate change (Gormezano andRockwell 2013, Petherick et al. 2021). There is reason
to believe that brown bears also sometimes view conspecifics as a food source—cannibalism among female
brown bears was documented to be associated with infanticide and conspecific strife, and brown bears regularly
kill dependent yearling cubs (Swenson et al. 2001). In
contrast, for other species such as American black bears
and Asiatic black bears that are less carnivorous, infanticide was entirely, and conspecific strife was primarily, amale behavior (e.g., Naganuma et al. 2021).
Although sexually selected infanticide is likely the primary cause for most infanticide events, there are exceptions. The most notable exception is when females killdependent young that are not theirs. For example, Hessing and Aummiler (1994) observed a female brown bearwith cubs that killed and ate 1 of 2 cubs belonging to adifferent bear and killed 2 cubs during a previous year.
This occurred at a salmon (Oncorhynchus spp.) spawning ground, where food availability was high and therefore killing cubs as a food source was unlikely and not
typically observed at such locations (L. Aumiller, Vital
Ground Foundation, pers. comm.). An attempted infanticide can also lead to a male bear killing an adult female(e.g., Tamatani et al. 2021), which does not fully support sexually selected infanticide, although such events
are often initiated by the male trying to increase his mating opportunities. For example, Dean et al. (1986) documented a male that initially tried to kill a cub, but whenthe mother intervened, the male killed and ate her. Variation in infanticide occurs throughout bear species, withsome events primarily occurring before mating seasons insome areas and after mating seasons in others (Shimozuru
et al. 2019). Reporting whether infanticide includes theconsumption of cubs could help reveal motivations forthe events that seem to be exceptions, but often such information is missing in the literature.
Cannibalism associated with scavenging, and to somedegree conspecific strife, seemed to be more directly
linked to viewing conspecifics as a food source comparedwith other forms of cannibalism, but neither is without
risk. Scavenging on bear carcasses that died from causes
other than intraspecific killing increases the risk of parasitic infection or disease (Moleón et al. 2017). For somespecies, there could be selection pressure against eating a dead conspecific, except when the benefits of the6 SHORT COMMUNICATION
Table 3. Instances of cannibalism by bears found from a review of social media and the internet. This includes
bear species, location, number and type of cannibalism, sex of cannibals, and the hyperlink for the event.
Species

Location

Cannibalism
Type ofeventscannibalism

Brown bear AK, USA

1

Brown bear Banff, AB,
CanadaBrown bear AK, USA
Brown bear Banff, AB,
CanadaPolar bear Unknown
Polar bear MB, Canada

1

Sex ofcannibal

1
1

ConspecificstrifeConspecificstrifeInfanticide
Infanticide

1
1

Infanticide
Scavenging

1

Undetermined

Male
Femalewith cubs
MaleHyperlink addressMale

https://youtu.be/XJDFG7cTlVs

Malehttps://www.cbc.ca/news/canada/calgary/grizzly-bear-eatsblack-bear-in-banff-1.1414994
https://youtu.be/t3DxCqU0oV0
https://www.cbc.ca/news/canada/calgary/banff-bear-grizzlysplit-lip-eat-ate-cubs-alberta-parks-canada-1.5557895
https://www.youtube.com/watch?v=Rfo233Q6aOg
https://youtu.be/xlkOP4OgSrI

Male
Male

AmericanBC, Canada
bear
Brown bear Banff, AB,
CanadaBrown bear Katmai National
Park, AK, USA
Polar bear Baffin Island,
NU, Canada
Polar bear MB, Canada

1

Undetermined

Male

1

Undetermined

Unknownhttps://www.cbc.ca/news/canada/british-columbia/bear-eatsbear-central-bc-1.4833151
https://calgaryherald.com/news/local-news/grizzly-bearknown-as-split-lip-eats-another-marked-grizzly-bear
https://www.nps.gov/katm/blogs/death-of-bear-130.htm

1UndeterminedMale

https://www.youtube.com/watch?v=MWbQyY6kfxc

8Undetermined

Male

Polar bear

1

UndeterminedMale

https://www.cbc.ca/news/canada/british-columbia/bear-eatsbear-central-bc-1.4833151
https://www.youtube.com/watch?v=UfRM0kRGqKc

food resource outweigh the risks of contracting a parasite or disease. However, bears are often food-limited,even when there are abundant resources, and are frequent
scavengers (Krofel et al. 2012, Allen et al. 2015, Inagaki
et al. 2020), which may make bears less wary of eating
conspecifics compared with the other, more predatory
carnivores. Most incidents of conspecific strife, whichcome with the risk of injury or death, were performed bymale bears, but there are exceptions, including one documented event of conspecific strife by a female American
black bear. This female had cubs of her own, and an abandoned cub attempted to associate with them, but the family group killed and consumed the foreign cub (Garrison
et al. 2007).
Although a direct link to increased fitness can be drawn
for some cases of cannibalism, in cases of filicide (wherea mother kills and eats her young), it appears to reduce
fitness by directly reducing the number of progeny. Filicide was rarely documented among bears, with 6 of the 8
events recorded for polar bears. Most of these events werewhen a mother killed a cub because it was starving or it
appeared unlikely to survive (Uspenski and Kistchinski
1972, Belikov and Kuprijanov 1977). There are also occasional cases where a cub does not emerge from a den,which may be the result of filicide or at least scavenging,and these should be explored in more depth when foundin the future. Hessing and Aummiler (1994) documented
a conspecific female that killed another female’s depen-

dent cub but then abandoned it, and the mother returnedand ate the cub. Although we counted this as scavenging
in our review, it again points to mothers trying to regainenergy invested in their cubs that are unlikely to, or donot, survive.
One drawback of our study is that it was limited to peerreviewed literature, but instances of cannibalism can bereported via other means, such as in gray literature (i.e.,theses and reports) or on social media. Our primary reason for not including gray literature is that there is no
way to systematically search and review gray literature.
Instances in gray literature are also often reported in peerreviewed literature, causing double-counting of the same
events. Events in social media have similar issues but alsolack the rigor of events documented in peer-reviewed literature. For instance, we performed an extensive reviewof the internet and social media (Table 3), but found very
few instances from social media, and the reports often
lacked important information such as date, time, and location. The cannibalism events reported in gray literature(e.g., Black and Auger 2004, Steyaert 2012) and social
media (e.g., Table 3) are no less important than those inpeer-reviewed literature, but we encourage authors in the
future to publish these events in peer-reviewed literatureso they can more easily be evaluated and used by thescientific community.
We did come across some lack of clarity that would be
helpful to address in future research. There were many

Unknown

Ursus 33:article e10 (2022)

ALLEN ET AL.
reports of infanticide, and although some authors assumed that cannibalism always accompanies infanticide(e.g., Davoli et al. 2018), most studies neglected to report whether or not the cubs were consumed after being killed. For the sake of our literature review of cannibalism, we only considered the cases where a conspecific was reported to be consumed, but this means that
our literature review may have underestimated cannibalism events by bears, especially cases of sexually selected
infanticide, which is the most common form of cannibalism. Although this generally is limited to infanticide,other studies seemed to confuse predation (killing a conspecific) with cannibalism (consuming a conspecific) or
considered the killing and consuming of a congeneric(different bear species) to be cannibalism (e.g., Mattson
et al. 1992). These unclear definitions limit the abilityof researchers to understand cannibalism, and we recommend in the future using definitions similar to those wehave provided in Table 1.
There were also several cases of cannibalism where thetype and cause could not be determined. Many of thesewere based on methods that do not allow determinationof the cause (e.g., bones and fur found through scat analyses), so we suggest in the future that researchers documenting cannibalism in the field record as many details as
possible. This includes noting age and sex of the cannibal;
age, sex, and reproductive status of the consumed bear;
exact location of the event and potential relocation of the
carcass; inspection of wounds; and consumption of the
carcass. Similar to guidelines for documentation of damages caused by predators on livestock (e.g., Černe et al.
2019), we recommend detailed photo-documentation of
the carcass, animal tracks, and other signs around thecarcass from various angles and distances together witha scale. Special attention should be given to wounds onthe carcass that occurred premortem, which can reveal
the cause of death but which often require flaying the
body parts with bite wounds. Crucial information for
the interpretation of the cannibalistic event is also relatedness between the consumer and the consumed bear,
which enable scientists to distinguish between filicide,siblicide, and sexually selected infanticide. Unless both
victim and consumer are previously known bears withestablished pedigrees, we recommend collecting genetic
samples of the victim, as well as the consumer. The latter is usually more difficult to obtain because of limited amount of DNA left at the site. One option is tosearch for a scat or hair around the carcass, or to takea saliva swab from the carcass (e.g., from the surrounding of the killing wound or at parts that were consumed;Černe et al. 2019). However, in most cases of cannibalism,
Ursus 33:article e10 (2022)

7

saliva swabs will result in mixed samples also containing the more numerous DNA from the consumed bear.
Such mixed samples often produce multiple alleles at ࣙ1loci or some of the consumer alleles may be completely
obscured, which significantly increases the complexityof the genetic analysis (Roon et al. 2005). But when apure sample from the victim (which usually can be easily
obtained from the tissues available) is analyzed in parallel, statistical approaches developed for human forensics can be applied to separate the consumer’s and victim’s genotypes and determine their relatedness (Hu et al.
2014). Following these recommendations will allow scientists to accurately document cannibalism and increase
our understanding of cannibalism among bears and othercarnivores.

Acknowledgments
We would like to thank the Illinois Natural History Survey, and the University of Illinois for their support. M.K.
was supported by the Slovenian Research Agency (grant
no. P4-0059). We thank Y. Goto for providing information. We also thank J. Swenson, S. Steyaert, S. Miller,and 2 anonymous reviewers for comments that greatly
improved the quality of the manuscript.

Literature cited
ALLEN, M.L., L.M. ELBROCH, C.C. WILMERS, AND H.U.
WITTMER. 2015. The comparative effects of large carnivores
on the acquisition of carrion by scavengers. American Naturalist 185:822–833.
———, A. INAGAKI, AND M.W. WARD. 2020. Cannibalism inraptors: A review. Journal of Raptor Research 54:424–430.
———, H.U. WITTMER, A. INGAKI, K. YAMAZAKI, AND S.
KOIKE. 2021. Food caching by bears: A literature review
and new observations for Asiatic and American black bears.
Ursus 32:e10.
ALT, G.L., AND J.M. GRUTTADAURIA. 1984. Reuse of black
bear dens in northeastern Pennsylvania. Journal of Wildlife
Management 48:236–239.
AMSTRUP, S.C., I. STIRLING, T.S. SMITH, C. PERHAM, AND G.W.
THIEMANN. 2006. Recent observations of intraspecific predation and cannibalism among polar bears in the southern
Beaufort Sea. Polar Biology 29:997–1002.
ARIMOTO, I., Y. GOTO, C. NAGAI, AND K. FURUBAYASHI. 2011.
Autumn food habits and home-range elevations of Japanese
black bears in relation to hard mast production in the beech
family in Toyama Prefecture. Mammal Study 36:199–208.
BALLESTEROS, F., G. PALOMERO, J.C. BLANCO, AND J.V.
LÓPEZ-BAO.2021. Sexually selected infanticide or predation? Killing and consumption of a female brown bear ina male infanticide attempt. European Journal of Wildlife
Research 67:1–4.

8 SHORT COMMUNICATIONBECHARD, M.J. 1983. Food supply and the occurrence of brood
reduction in Swainson’s hawk. Wilson Bulletin 95:233–242.
BELIKOV, S.E., AND A.G. KUPRIJANOV. 1977. Behavior of thepolar bear on Wrangel Island. The Polar Bear and its Conservation in the Soviet Arctic: Collection of Scientific Papers.
Moscow: Central Laboratory for Nature Conservation 40:55.
BELLEMAIN, E., J.E. SWENSON, AND P. TABERLET. 2006. Mating strategies in relation to sexually selected infanticide
in a non-social carnivore: The brown bear. Ethology 112:
238–246.
BLACK, H.L., AND J. AUGER. 2004. Black bears of Utah’s East
Tavaputs Plateau: Final report for Utah Division of Wildlife
Resources. Utah Division of Wildlife Resources, Salt Lake
City, Utah, USA.
BOJARSKA, K., AND N. SELVA. 2012. Spatial patterns in brownbear Ursus arctos diet: The role of geographical and environmental factors. Mammal Review 42:120–143.
ČERNE, R., M. KROFEL, M. JONOZOVIČ, A. SILA, H.
POTOČNIK, M. MARENČE, P. MOLINARI, J. KUSAK, T.
BERCE, AND M. BARTOL. 2019. A fieldguide for investigating damages caused by carnivores: Brown bear, grey
wolf, golden jackal, red fox, Eurasian lynx. Slovenia Forest Service - LIFE DINALP BEAR project, Ljubljana,
Slovenia. https://dinalpbear.eu/wp-content/uploads/GIDC_
ENG_v34_web.pdf. Accessed 4 Mar 2022.
DAVIS, H., AND A.S. HARESTAD. 1996. Cannibalism by blackbears in the Nimpkish Valley, British Columbia. Northwest
Science 70:88–92.
DAVOLI, F., M. COZZO, F. ANGELI, C. GROFF, AND E. RANDI.
2018. Infanticide in brown bear: A case-study in the ItalianAlps–Genetic identification of perpetrator and implications
in small populations. Nature Conservation 25:55–75.
DEAN, F.C., L.M. DARLING, AND A.G. LIERHAUS. 1986. Observations of intraspecific killing by brown bears, Ursus arctos.
Canadian Field-Naturalist 100:208–211.
DEROCHER, A.E., AND Ø. WIIG. 1999. Infanticide and cannibalism of juvenile polar bears (Ursus maritimus) in Svalbard.
Arctic 52:307–310.
———, ———, AND M. ANDERSEN. 2002. Diet compositionof polar bears in Svalbard and the western Barents Sea. Polar
Biology 25:448–452.
———, ———, AND G. BANGJORD. 2000. Predation of Svalbard reindeer by polar bears. Polar Biology 23:675–678.
DYCK, M.G., AND K.J. DALEY. 2002. Cannibalism of a yearlingpolar bear (Ursus maritimus) at Churchill, Canada. Arctic
55:190–192.
ELOWE, K.D., AND W.E. DODGE. 1989. Factors affecting black
bear reproductive success and cub survival. Journal of
Wildlife Management 53:962–968.
GARRISON, E.P., J.W. MCCOWN, AND M.K. OLI. 2007. Reproductive ecology and cub survival of Florida black bear. Journal of Wildlife Management 71:720–727.
GÓMEZ, J.M., M. VERDÚ, AND A. GONZÁLEZ-MEGÍAS. 2021.
Killing conspecific adults in mammals. Proceedings of theRoyal Society B 288:20211080.

GORMEZANO, L.J., AND R.F. ROCKWELL. 2013. What to eat
now? Shifts in polar bear diet during the ice-free season in western Hudson Bay. Ecology and Evolution 3:
3509–3523.
HESSING, P., AND L. AUMILLER. 1994. Observations of conspecific predation by brown bears, Ursus arctos, in Alaska.
Canadian Field-Naturalist 108:332–336.
HRDY, S.B., 1979. Infanticide among animals: A review, classification, and examination of the implications for the reproductive strategies of females. Ethology and Sociobiology
1:13–40.
HU, N., B. CONG, S. LI, C. MA, L. FU, AND X. ZHANG. 2014.
Current developments in forensic interpretation of mixed
DNA samples. Biomedical Reports 2:309–316.
INAGAKI, A., M.L. ALLEN, T. MARUYAMA, K. YAMAZAKI,K. TOCHIGI, T. NAGANUMA, AND S. KOIKE. 2020. Vertebrate scavenger guild composition and utilization of carrion
in an East Asian temperate forest. Ecology and Evolution
10:1223–1232.
IVANOV, E.A., I.A. MIZIN, A.G. KIRILOV, N.G. PLATONOV, I.N.
MORDVINTSEV, S.V. NAIDENKO, AND V.V. ROZHNOV. 2020.
Observations of intraspecific killing, cannibalism, and aggressive behavior among polar bears (Ursus maritimus) inthe eastern Barents Sea and the Kara Sea. Polar Biology
43:2121–2127.
JONKEL, C. 1970. The behavior of captured North American
bears (with comments on bear management and research).
Bioscience 20:1145–1147.
JONKEL, C.J., AND I.M. COWAN. 1971. The black bear in the
spruce–fir forest. Wildlife Monographs 27:3–57.
KARAMANLIDIS, A.A., J.J. BEECHAM, C. CHATZIIOANNOU, M.
DE GABRIEL HERNANDO, K. GRIVAS, L. KRAMBOKOUKIS,AND G. PAPAKOSTAS. 2015. Intraspecific predation on a
subadult brown bear in Greece. Ursus 26:7–10.
KOLCHIN, S.A. 2019. The first record of cannibalism in the
Asiatic black bear (Ursus thibetanus) in the Russian Far
East. Zoologichesky Zhurnal 98:222–226.
KROFEL, M., I. KOS, AND K. JERINA. 2012. The noble cats
and the big bad scavengers: Effects of dominant scavengers
on solitary predators. Behavioral Ecology and Sociobiology
66:1297–1304.
LECOUNT, A.L. 1987. Causes of black bear cub mortality.
Bears: Their Biology and Management 7:75–82.
LINDZEY, F.G., AND E.C. MESLOW. 1977. Population characteristics of black bears on an island in Washington. Journalof Wildlife Management 41:408–412.
LUNN, N.J., AND G.B. STENHOUSE. 1985. An observation of
possible cannibalism by polar bears (Ursus maritimus).
Canadian Journal of Zoology 63:1516–1517.
MATTSON, D.J. 1997. Use of ungulates by Yellowstone grizzly
bears Ursus arctos. Biological Conservation 81:161–177.
———, R.R. KNIGHT, AND B.M. BLANCHARD. 1992. Cannibalism and predation on black bears by grizzly bears in the
Yellowstone ecosystem, 1975–1990. Journal of Mammalogy 73:422–425.

Ursus 33:article e10 (2022)

ALLEN ET AL.
MILLER, J.A., T.S. SMITH, J. AUGER, H.L. BLACK, AND L.
ALLPHIN. 2017. The late-denning activities of the American black bear in Utah. Ursus 27:78–89.
MILLER, S.D., R.A. SELLERS, AND J.A. KEAY. 2003. Effects ofhunting on brown bear cub survival and litter size in Alaska.
Ursus 14:130–152.
MOLEÓN, M., C. MARTÍNEZ-CARRASCO, O.C. MUELLERKLEIN,
W.M. GETZ, C. MUÑOZ-LOZANO, AND J.A. SÁNCHEZZAPATA. 2017. Carnivore carcasses are avoided by carnivores. Journal of Animal Ecology 86:1179–1191.
NAGANUMA, T., M. TANAKA, S. TEDUKA, S. STEYAERT, K.
TOCHIGI, A. INAGAKI, H. MYOJO, K. YAMAZAKI, AND S.
KOIKE. 2021. Animal-borne video systems provide insight
into the reproductive behavior of the Asian black bear. Ecology and Evolution 11:9181–9190.
NANSEN, F. 1897. Farthest North. Volume 2. MacMillan andCompany Ltd., London, UK.
NARITA, R., A. SUGIMOTO, AND A. TAKAYANAGI. 2006. Animalcomponents in the diet of Japanese black bears Ursus thibetanus japonicus in the Kyoto area, Japan. Wildlife Biology
12:375–384.
OBBARD, M.E., AND E.J. HOWE. 2008. Demography of blackbears in hunted and unhunted areas of the boreal forest of
Ontario. Journal of Wildlife Management 72:869–880.
OLSON, T.L. 1993. Infanticide in brown bears, Ursus arctos, atBrooks River, Alaska. Canadian Field-Naturalist 107:92–94.
ORDIZ, A., M. KROFEL, C. MILLERET, I. SERYODKIN, A.
TALLIAN, O.G. STØEN, T.R. SIVERTSEN, J. KINDBERG, P.
WABAKKEN, H. SAND, AND J.E. SWENSON. 2020. Interspecific interactions between brown bears, ungulates, and otherlarge carnivores. Pages 36–44 in M. Melletti and V. Penteriani, editors. Bears of the world: Ecology, conservationand management. Cambridge University Press, Cambridge,
Massachusetts, USA.
PAROVSHCHIKOV, V. 1964. A study of the population of thepolar bear of Frans Joseph Land. Acta Sociologia Zoologica
Bohemoslov 28:167–177.
PETHERICK, A.S., J.D. REUTHER, S.J. SHIRAR, S.L. ANDERSON, AND L.R. DESANTIS. 2021. Dietary ecology of Alaskanpolar bears (Ursus maritimus) through time and in response to Arctic climate change. Global Change Biology 27:
3109–3119.
ROON, D.A., M.E. THOMAS, K.C. KENDALL, AND L.P. WAITS.
2005. Evaluating mixed samples as a source of error in
non-invasive genetic studies using microsatellites. Molecular Ecology 14:195–201.
SAKAMOTO, Y., AND T. AOI. 2006. Food habits of the Asiatic
black bear Ursus thibetanus japonicas in the northern Ohu
Mountains, Japan. Bulletin of the Iwate University Forests
37:17–27. [In Japanese with English abstract.]
SHIMOZURU, M., Y. SHIRANE, H. TSURUGA, M. YAMANAKA,
M. NAKANISHI, T. ISHINAZAKA, S. KASAI, T. NOSE,

Ursus 33:article e10 (2022)

9

Y. MASUDA, Y. FUJIMOTO, AND T. MANO. 2019. Incidenceof multiple paternity and inbreeding in high-density brownbear populations on the Shiretoko Peninsula, Hokkaido,
Japan. Journal of Heredity 110:321–331.
STEYAERT, S. 2012. The mating system of the brown bear in
relation to the sexually selected infanticide theory. Dissertation, Norwegian University of Life Sciences, Ås, Norway.
STEYAERT, S.M., C. REUSCH, S. BRUNBERG, J.E. SWENSON,
K. HACKLÄNDER, AND A. ZEDROSSER. 2013. Infanticide asa male reproductive strategy has a nutritive risk effect inbrown bears. Biology Letters 9:20130624.
STIRLING, I., E. RICHARDSON, G.W. THIEMANN, AND A.E.
DEROCHER. 2008. Unusual predation attempts of polar bears
on ringed seals in the southern Beaufort Sea: Possible significance of changing spring ice conditions. Arctic 61:14–22.
———, AND J.E. ROSS. 2011. Observations of cannibalism bypolar bears (Ursus maritimus) on summer and autumn sea
ice at Svalbard, Norway. Arctic 64:478–482.
STONE, I.R., AND A.E. DEROCHER. 2007. An incident of polar
bear infanticide and cannibalism on Phippsoya, Svalbard.
Polar Research 43:171−173.
SWENSON, J.E. 2003. Implications of sexually selected infanticide for hunting of large carnivores. Pages 171–189 in M.
Festa-Bianchet and M. Apollonio, editors. Animal behavior
and wildlife management. Island Press, Covelo, California,
USA.
———, B. DAHLE, AND F. SANDEGREN. 2001. Intraspecificpredation in Scandinavian brown bears older than cubs-ofthe-year. Ursus 12:81–91.
———, F. SANDEGREN, A. SÖDERBERG, A. BJÄRVALL, R.
FRANZEN, AND P. WABAKKEN. 1997. Infanticide caused byhunting of male bears. Nature 386:450−451.
TAMATANI, H., A. HIORNS, AND T. YAMAMOTO. 2021. An apparent case of infanticide in the Asiatic black bear in Japan.
Ursus 32:e16.
TAYLOR, M., T. LARSEN, AND R. SCHWEINSBURG. 1985. Observations of intraspecific aggression and cannibalism in polar
bears (Ursus maritimus). Arctic 38:303–309.
TIETJE, W.D., B.O. PELCHAT, AND R.L. RUFF. 1986. Cannibalism of denned black bears. Journal of Mammalogy 67:762–
766.
TROYER, W.A., AND R.J. HENSEL. 1962. Cannibalism in thebrown bear. Animal Behavior 10:3–4.
USPENSKI, S.M., AND A.A. KISTCHINSKI. 1972. New data on thewinter ecology of the polar bear (Ursus maritimus Phipps)
on Wrangel Island. Bears: Their Biology and Management
2:181–197.

Received: November 2, 2020
Accepted: December 3, 2021
Associate Editor: S.M.J.G. Steyaert