- Jan 12, 2012
This is the most epic natural battle, nowhere else in the world do 2 apex and extremely powerful land predators overlap (apart from the extremely rare Polar Bear/Brown Bear interactions). People really should make a documentary on Siberian Tiger/Brown Bear interaction.
Here is the best information I found on a different forum about Siberian Tigers vs Brown Bears,
01 - PREDATION
1a - Predation on bears
Tigers are strictly predatory animals and hunt whatever is available. In the RFE, bears are abundant and therefore hunted on a regular basis. Both black and brown bears are hunted. In some areas and periods, smaller black bears are targeted (modern research). In other areas (Tkachenko, 1997) and periods (Bromlej, 1965, as well as modern research), brown bears are more often hunted. Preferences, it seems, depend on (relative) abundance, availability and other (unknown) factors.
Most bears taken are small and medium-sized animals (Chapter 19). Larger bears are killed less frequently. Adult tigresses have been known to hunt adult female black bears (Sysoev), smallish but adult female brown bears (Kaplanov, 1948) and, occasionally, (immature) brown bears exceeding their own weight (Bromlej, 1965). Adult male tigers hunt adult male black bears (Sysoev, 1960 and Tkachenko, 1997), who, according to KTKC, average 183 kg. in north-eastern China. Some male tigers, as was stated by Kaplanov (1948), Bromlej (1965) and Goodrich (in Seryodkin et al, 2005), hunt adult brown bears on a regular basis, but it seems even these specialists target adult females with cubs only (Chapter 19 and posts 247, 33, 350 and 353).
Adult female brown bears, according to Kucerenko, average 189 kg. (range 120-280 and, according to KTKC, up to 360 kg.), whereas adult male tigers average 175-195 kg. (WCS and Miquelle). Most adult females (brown bears) killed are somewhat smaller than an average adult male tiger (Chapter 19), but some females are similar or near-similar in size. Recent research confirms Bajkov's (1925) statement that tigers are able to hunt brown bears of up to almost their own weight.
1b - Predation on large brown bears
There are reliable reports on large brown bears killed by tigers, but the number is very limited indeed and it also is a fact 'large', apart from one exception (Bromlej, 1965), was never specified. All incidents mentioned below occured before 1970 and it is in this respect interesting to note Russian researchers evaluating records on the size of Siberian tigers noticed a gradual decline in weight in Siberian tigers in the last century. It seems the decline started about a century ago and continued to roundabout 1970 (post 436).
W.J. Jankowski (in Mazak, 1983) shot a very large (11.6 'over curves' and about 300 kg.) male tiger in Heilongjiang (north-eastern China) in July 1943. Very close to the tiger, Jankowski found the remains (head and paws) of a 'very large' male brown bear which had been killed and eaten by the tiger some days before he was shot (unpublished letter, dated May 8, 1970). This report, however, was never mentioned by researchers and both Jankowski and Mazak, apart from a photograph of the tiger and the letter mentioned, did not provide crucial details on the bear. Too detailed to dismiss and too meagre to accept, one could conclude.
K.G. Abramov (unpublished notes, provided to Mazak by Abramov's widow in 1966) also reported on a male tiger who had killed an 'old, large male Schatun' in the 1958-1959 winter (in the Central Sichote-Alin Mountains). This case wasn't dismissed, but researchers apparently concluded the sex of the brown bear was unclear.
Bromlej (in Heptner and Sludskij, 1980, page 149), in May 1951, found the remains of a 158 cm. (way of measuring unknown) and 170 kg. (approximately) brown bear killed by a tigress near the Tatibe River. The tigress remained 3-4 days near the kill and consumed the fattiest parts. Although Bromlej didn't state anything on the age and sex of the bear, research (in two threads) showed he was misquoted by both Mazak (1983) and Heptner and Sludskij (1980). One American female researcher, in her mail to Bonns, even stated she knew of a " ... good-sized male killed in or near its den in 1951 ... ". It is not known in which circumstances the bear was killed and Bromlej didn't make statements regarding the struggle. The incident, however, is well authenticated and shows a tigress is able to kill a larger bear.
Rakov also referred to a 'large brown bear' killed by a tiger in December 1959 near the Svetlaya River. The tiger remained 5-10 days near the kill. The gender wasn't established. Kaplanov (1948) also mentioned an incident of predation on a 'large' brown bear. Again, details were not provided.
The level of predation differs. In some areas, predation on bears is limited, whereas the situation in other areas is very different. It also has to be noted predation has a seasonal character. Most studies indicate bears (black and brown together) constitute between 1-1,5% (recent research) and 8,4% (V.K. Abramov, 1962) of the total food-intake of tigers. In some areas, however, the percentage (up to 37%) is much higher (Tkachenko, 1997).
Adult male tigers hunt bears more often than adult females (Chapter 19). Although only three cases of predation have been described, it seems unlikely all of the bears killed in fights near kill sites (post 55) were killed by adult male tigers. It also seems unlikely tigresses, as was suggested by some researchers, only very rarely hunt bears. The skill of the tigress described by Kaplanov (1948), suggests some tigresses could be experienced regarding bears.
1c - Predation on tigers
Bears do not habitually hunt tigers, but it is known adult male brown bears consume tigers killed in disputes. It seems some adult male brown bears, in some circumstances, deliberately target tigers (posts 520 and 536). Kostoglod mentioned a case in which a bear followed a tiger for a long distance (Chapter 19). The tiger escaped, but another one was attacked, killed and eaten. Although tigresses sometimes perish in fights with male brown bears, the number is incidents is too limited to get to general statements.
In 2010, two tigresses, a subadult (19 months of age) and an 8-year old ('Vera') with two (about 18 months old) cubs, were killed by brown bears (post 520). Apart from the fact they were killed by brown bears, not much was known. The young tigress, behaviourwise, showed signs of disease and it is also known at least 4 other tigers (two subadult males, one adult female and one adult male) displayed abnormal behaviour before their death (Miquelle). There is no additional information on the 8-year old tigress mentioned above.
In the last 50 years, according to Alexious3, at least two adult male tigers have been killed by brown bears (post 568). One perished in 1960 and it could be this is the case used by Sysoev for his fictional story on 'Amba'. Another tiger died after a fight in 1972. Rukovsky mentioned another incident (post 70). Two of the three male tigers killed, at roundabout four years of age, were young adults. The third one was described as a medium-sized animal (age unknown).
There are other accounts of male tigers killed by brown bears (Sysoev mentioned two cases and Bonns mentioned an incident near or in a river in 1943), but these, as far as is known, have not been acknowledged by researchers. The number of tigers killed in fights between 1943-1996 (referring to the table posted earlier) indicate there could be more cases (posts 17 and 55). Apart from one, all fights referred to in the table (post 55) were corroborated by Russian researchers, but in most incidents details were missing. It is, however, known brown bears were involved in most incidents.
The information available suggests most tigers killed were killed in winter. As brown bears hibernate in winter, it has to be assumed non-hibernating bears ('Shatuns') were involved in most of these. Schatuns are desperate animals and most seem to perish. This means many would be inclined to attack any animal, tigers and other (hibernating) bears included (post 584).
Although at least one was a smallish female who killed and ate a much larger hibernating male brown bear, most Schatuns seem to be males. As most of the 'large brown bears' killed by tigers mentioned above were killed in winter, it has to be assumed some, if not all, of these were Schatuns. Same for tigers killed in winter.
1d - Conclusions
Tigers in the RFE habitually hunt brown bears for food. Not the other way round. Most bears killed are small to medium-sized animals. Even adult male tigers specialising on brown bears seldom target bears of their own size. Adult females, however, have been killed more than once and there is no doubt (Bromlej, 1965) a tiger is able to kill a larger brown bear.
There are reliable reports on large brown bears killed by tigers. But 'large', apart form the bear killed in the 1951 incident, was never substantiated and most bears were killed in winter, indicating Schatuns were involved in most. Schatuns are desperate animals, willing to attack anything they encounter. When Schatuns attack adult male tigers, fights erupt and these can go either way. It seems Schatuns were involved in most of the few incidents with a tragic outcome.
Some Russian researchers think some adult male brown bears sometimes deliberately target and attack tigresses with cubs in favourable circumstances (snowy conditions). Although it is known tigresses sometimes perish in encounters with male brown bears, the number is too limited to get to conclusions.
02 - THE SIZE OF LARGE BEARS KILLED BY TIGERS
Tigers, as was stated before (Bromlej, 1965), are capable of killing a larger bear. The bear killed near the Tatibe River, at 158 cm. and approximately 170 kg., could have been a large subadult animal (post 448). Bromlej didn't state anything on the tigress. It is, however, known adult tigresses average between 115-120 kg. (post 83). As males, averaging between 175-195 kg. (WCS - Miquelle), are significantly larger, it is likely an experienced male tiger is capable of tackling bears well in excess of his own weight as well. It has to be stated, however, there is, apart from the incident mentioned by Mazak, no evidence.
There are, however, reliable reports on 'large brown bears' killed by tigers and most of these involved non-hibernating brown bears (Schatuns). As these will attack any animal, it could be some of the tigers attacked had no option but to engage the bear. As fights between animals of similar or near-similar size can go either way, some 'Schatuns', it is assumed, were killed. Encounters of this nature, however, can't be regarded as deliberate predatory attacks on healthy adult male brown bears.
It seems male tigers avoid even hibernating large brown bears most of the time. But most of the time isn't equal to always (Bromlej, 1965 and Kaplanov, 1948) and this observation can't be used to state male brown bears win mosts fights with tigers. If both are of similar size, it apparently depends (posts 55, 462, 463, 465, 470, 495 and 566).
03 - INTERACTIONS BETWEEN ADULT MALES
Adult male brown bears, according to Russian researchers, often follow tigers in order to feed on their kill. The outcome of the interactions isn't easy to describe. In some cases, one of the two is chased. In others, bears wait for their turn. Sometimes (in all four cases adult tigresses were involved) both feed simultanously. Every now and then, tigers, including adult males (one case was described in Chapter 19), are displaced by bears. Disputes erupt at times. The information available suggests brown bears are more agressive, whereas tigers (referring to all brown bears involved and not to male brown bears in particular) win most fights. The margins, however, seem to be small (posts 55, 463). Details on the animals involved in these fights (sex, age and size) often are absent.
Adult male brown bears and adult male tigers seem to avoid each other. In difficult circumstances (a lack of food), they sometimes clash near kill-sites. The observations made in over half a century suggest an all-out fight between a full-grown male tiger and a full-grown male brown bear has to be regarded as a singular event. The list of victims is very limited.
Three fights were witnessed (Sysoev) or pieced together (Rukovsky). In two incidents, the tigers were young adults (3-4 years of age), whereas the brown bears (all three incidents) were described as 'large' or 'very large' animals. In all fights, the tigers were killed after a prolonged struggle. The margins, it seems, were small.
The number of 'large' brown bears killed by tigers (referring to the five incidents mentioned above) is very limited as well. Two of the four bears killed were described as oldish animals. The information available suggests, as Gorokhov stated, inexperienced, young (tigers) or old (bears) animals seem to be more vulnarable than mature, healthy animals.
04 - CONTRADICTORY INFORMATION (researchers)
The lack of clarity on the outcome of disputes near kill-sites is a result of a lack of specific information on one hand and contradictory statements of researchers on the other hand.
Miquelle, for instance, stated adult tigers are not always able to defend their kill against male brown bears (1) and brown bears have been known to kill tigers (2), but he also stated brown bears do not win all encounters, as some tigers had learned to hunt them (3). Which is not easy to understand, as there is a difference between open encounters and ambushes. His statements differ from Kostoglod´s, who (posts 164, 182) stated brown bears are capable to kill tigers (4). Rukovsky, on the other hand, stated an average tiger is always stronger than an average bear (5) and tigers won most of the fights he knew of (6). He, however, also mentioned an incident in which a young adult male tiger (post 70), after a prolonged battle, was killed by a very large brown bear (7).
The confusion not only is a result of a lack of specific information and contradictions. It also is likely the shape and the outcome of an encounter depends on the gender, age and size of both animals involved (8). In many cases, this information is lacking.
Finally, it has to be stated the observations of modern research regarding the relation between tigers and bears do not confirm those of Kaplanov and Bromlej. Kaplanov, from the tracks in the snow, saw brown bears, one of these a very large animal, avoid tiger tracks (9), whereas modern researchers state brown bears often deliberatey follow the tracks of tigers (10). Bromlej stated tigers hunted even large hibernating brown bears (11), of which the largest were able to escape, but his observations were not confirmed by modern research (12).
05 - OTHER FACTORS
Although the evidence for such a statement is lacking, it seems 'large brown bears' are not entirely out of the predatory reach of adult male tigers. As it is difficult to get to clear statements regarding interactions between male tigers and male brown bears, other factors are discussed below.
5a - The effect of hibernation.
Although an average adult male brown bear (Ursus arctos lasiotus) in the RFE, at 264 kg. (not known if spring, autumn or year-round weight), outweighs an average adult male tiger (195 kg.), a signifiant minority of adult male brown bears is weightwise well within reach of an average male tiger (Kucerenko, 2003). Furthermore, it has to be noted some male tigers exceed 250 kg. at times (Bajkov, 1925; Morden, 1930 and Mazak, 1983).
Adult male brown bears are subject to significant seasonal variations in weight. In northern Europe, where they averaged 273 kg. in late fall, they lost 72 kg. (or 26% of their autumn weight) during hibernation (post 406). Assuming brown bears in northern Europa compare to Ursus arctos lasiotus, one could state an average male brown bear in Russia could be vulnarable in late winter and early spring, when they would have lost about a quarter (roundabout 145 pounds) of their autumn weight. It is, however, very interesting to note brown bears (in general) are more often targeted in late fall and early winter (at their peak, that is) than in spring.
5b - Size
Male brown bears are sexually mature at about 5 years of age, but continue to grow until they are about 12 years of age and seem to put on weight even after that (posts 29, 283, 288, 315, 364, 370, 391, 394, 395, 408). The statistics available (on the growth rate of young and adolescent animals and the differences in size between sexually mature and full-grown males from North-America), indicate young animals can easily double their weight in a period of two years (Warsaw, jan. 16, 2010, 21:10:10). They also indicate there is a significant difference in skull size and weight between adult and full-grown male brown bears (posts 394, 408, 409, 431).
Adult males of Ursus arctos lasiotus (Kucerenko, 2003) average 264 kg. (range 260-321) in weight and 196 cm. in head and body length. It is assumed the average for weight refers to a year-round average. It also is assumed the animals were measured 'over curves'. Adult males (Baryshnikov, 2007) average 407,8 mm. (n=19) in greatest skull length (range 373,8-447,0 mm.).
Adult male tigers (WCS, first decade of this century) average 175-185 kg. (range 125-205 kg.), but it has to be added at least three of the tigers used for the table, judging from the other measurements provided, seemed immature. It also has to be stated the table did not include the heaviest tiger actually weighed (474 pounds), while another large animal (T-16) also wasn't measured and weighed. Furthermore, it has to be stated most, if not all, adult males captured and measured after the table was published were close to (or slightly over) 200 kg., meaning Miquelle's assessment (430 pounds or 195 kg.) could well prove to be right in the end. On it other hand, it has to be added tigers classified as 'problem tigers' usually are smaller. If all weights were to be included (reliable historical weights and new data not incorporated in the table mentioned above) for a realistic assessment, one could state the great majority of healthy, mature (at least 5 years of age) tigers average between 150-225 kg. (range 125-255).
Although Jankowski's tiger (which was 11.6 'over curves' and estimated at about 300 kg.) was not included, it is, judging from the size of this tiger and some captive tigers (like the 319 cm. tiger measured by Mazak and the 320 cm. tiger measured by Dr. Gewalt), to be expected animals exceeding the upper ranges mentioned will be encountered every now and then.
Adult male tigers average between 360-370 mm. (range 341-383) in greatest skull length. Both Bajkov and Kitchener referred to a skull close to 16 inches (406 mm.) in total length (more information on size in posts 217, 283, 300, 333, 363, 409).
5c - Hypothetical remarks regarding the impact of the factors mentioned
Most trainers I interviewed (posts 462, 463, 465 and 470) stated a fight between two healthy animals of similar size and age (referring to bears, tigers and lions) would be a toss-up. If one has a significant advantage, like weight, it is expected to count most of the time if it is assumed all other factors are similar or near-similar..
In the RFE, adult male brown bears are both shorter (head and body length in a straight line) and heavier than adult male tigers, meaning they have a more solid structure. In a prolonged struggle and all other factors considered equal, it is to be expected this advantage would count in the end. But the other factors are not similar.
Tigers seem to be as strong (post 70) and, for the ability to struggle on their hindlegs, almost compare to brown bears, experts state. They also state tigers are faster, more agile and more agressive in the initial stage of a fight, enabling them to manouvre the bear into a position in which they are able to use their teeth first. Furthermore, a tiger is able to exercise more pressure at the tip of the canines, which are decidly longer and as strong as well. According to Ursus arctos middendorffi, an average male brown bear fighting an average male tiger faces an enemy who, teethwise, compares to a brown bear much (about 50%) heavier than himself (more information in the posts of Ursus arctos middendorffi in the thread 'Morphological comparison of big pantherines and brown bears'). Tigers, therefore, are better biters.
It also is a fact a tiger, at equal or near-equal size, is able to pull (biceps) harder than a brown bear. This means a tiger, confronting the bear in an upright position, is able to hold a bear better than the other way round. Bears, on the other hand, are better pushers (triceps and shoulders) and more prolific hitters.
All this means an average male tiger, in spite of the difference in weight, can be expected to confront a larger average male brown bear on equal or near-equal terms. As his way of fighting is energy-absorbing, tigers need and seek breaks. It is, however, doubtful if a tiger, as Pikunov suggested, would expend himself in this way, as the information available (on fights with other animals) suggest tigers often are involved in prolonged struggles.
Bears able to turn the tables, according to trainers (and Sysoev, for that matter), often are experienced animals who adopt a defensive strategy in the initial stages of the fight. This strategy is facilitated by the ability to absorp significant damage and break the hold of a tiger, which is a feat in itself. All trainers state bears, because of their structure, are very difficult to kill. It takes a lot of time and energy and it seems bears know how to use breaks to force a decision. Meaning bears able to win a fight with a tiger use their qualities in a clever way. But they have to turn the tables in many fights, it seems. An experienced tiger able to evaluate the development of a fight would pull out. Young adult animals, however, often overestimate their chances and sometimes pay.
These notions were borne out by observations in captivity and observations of Sysoev (directly) and Rukovsky (indirectly). Sysoev (who witnessed two fights between young adult male tigers and male brown bears) and Rukovsky (who was able to piece the event together) both stated the youngish (about 4 years of age) male tigers, after a prolonged battle, were killed by significantly larger bears. In both incidents, the tigers, it seems, refused to pull out of the fight.
5d - Experts
Kretzchmar based his opinion on bears and tigers on Sludskij's book 'Lord of the jungle', interviews with hunters and his own experiences. He, like Bajkov, Sysoev and Sludskij, thought tigers would be able to cope with bears up to his own weight (roundabout 200 kg.) more often than not. After the limit mentioned, the balance would shift (posts 442, 481, 490-493 and 498). Meaning adult male brown bears would be out of range for an average adult male tiger.
But he also stated not one of the two consistently dominated the other in a fysical fight. Finally, he, in his book ('Shaggy God'), stated adult male tigers are not always willing to defend their kill in a dispute with " ... the clumsy giant ... ".
Small advantage for the bear, but not quite clear, one could conclude. If understood correctly, Kretzchmar, stated the difference in weight between both (very large brown bears excluded) wouldn't be decisive in a fight. Other factors would and it could be these do not relate to size, but to fundamental differences between both animals (posts 462, 463, 465, 468, 527).
A bear, as a non-hunter desperate for protein (male brown bears eat more meat than females), would be more willing to engage than a tiger because it (the appropiation of kills) is his livelihood, whereas a tiger can hunt again and isn't prepared to accept risks. Brown bears, for that reason, ultimately would dominate the food competition (posts 516, 561, 566). But every animal has a different character and it could be some tigers react different than others. In an all-out fight, the outcome is unsure. It depends.
5e - Trainers (captivity)
In a fight, all other factors equal, character, attitude and experience count. The trainers I interviewed stated tigers, more often than not (and more dependant on individuality), try to avoid confrontations. When they decide to get involved in a fight, tigers don't fight for dominance (lions) or food (bears), but for other reasons. Most, again according to trainers, will fight till a decision is reached. This attitude could explain why many fights end the way they do (post 55).
Tigers, according to all trainers interviewed, are ferocious critters. But so are brown bears. The two researchers interviewed by Bonns (D. Pikunov one of these) regarded brown bears (both sexes) as very dangerous animals. In the RFE, they are much more feared than tigers.
Bears (species related) also are bolder than tigers and tend to overestimate their capabilities in a fight with a tiger. Althought there are no strict rules regarding the outcome of a fight between two animals of similar size and age, tigers, although the margins are small, seem to win most encounters with bears because of the reasons mentioned.
It could be Kretzchmar, regarding the limit he proposed, is right. The list of large bears killed in fights in captivity seems to be as short as the list discussed earlier. Most trainers think Kretzchmar's limit is a bit low, because captive Siberian tigers are larger than their wild relatives. Most adult males average between 480-500 pounds (range 380-700) and all trainers stated they would not be willing to make a bet on the outcome of a fight.
It could be the trainer interviewed by Bonns ('Dan') worded the opinion of many trainers best. He stated a 500-pound male tiger would not be able to defeat a 600-pound male brown bear in a fair scrap. But he also stated an attack from behind would result in a dead bear.
06 - CONCLUSIONS
The information discussed above suggests the outcome of a fight between adult males is unsure when both are of similar size. Tigers are able to ambush larger bears (posts 58, 448, 453), but it is generally accepted male brown bears, who outweigh male tigers by quite a margin, dominate the food competition in normal circumstances.
Although the fights witnessed prove both are able to kill each other, the margins seem to be small. Mature animals (both species) only very seldom, if ever, succumb and the list of victims is very short indeed.
Some last remarks to finish with. Tigers and brown bears have been living in close proximity for a very long time. Although tigers hunt (young and medium-sized) brown bears on a regular basis, the impact on the population is very limited. One would expect this situation also is a result of the relative size of average adult males, meaning male brown bears would not be targeted by male tigers. This relative immunity would enable male brown bears to reproduce at a rate which limits the impact of predation.
The evidence there is (collected in a period of more than half a century) suggests this is indeed the case. Meaning mature and healthy adult male brown bears seem to be out of the predatory reach of adult male tigers. And, as far as is known, the other way round. Animals killed in fights (both species) are few and far between and it seems most, if not all, are inexperienced (tigers), oldish (bears) or incapacitated (malnourished Schatuns) animals.
It could be more is going on than is observed, but this seems to be the general rule. Meaning mature adult male brown bears dominate the food competition most of the time and, as was concluded by Russian researchers a long time ago, seem to have the edge in encounters. But most of the time isn't equal to always and the margins seem to be very small. Too small to engage in all-out fights on a regular basis.
- Feb 28, 2011
I am not sure what the body fat % is of Ursus arctos lasiotus.
- Aug 1 2012, 10:23 PM
- Aug 1 2012, 12:29 PM
It could be the trainer interviewed by Bonns ('Dan') worded the opinion of many trainers best. He stated a 500-pound male tiger would not be able to defeat a 600-pound male brown bear in a fair scrap. But he also stated an attack from behind would result in a dead bear.
Great informative post, thanx!
As for the statement above, I think weight informations about bears don't tell us much if the time of the year isn't specified. A 600 lbs bear before denning would likeley have less muscle mass and less fitness than a 500 lbs bear in early summer (assuming both being healthy animals in their prime). In such a case (600 lbs in autumn), a 500 lbs tiger would hold the advantage despite the weight difference. If 264 kg is the year-round
average for U. arctos lasiotus
, IMO the average individual of this subspecies would have the edge against an average 180-190 kg Amur tiger.
Knowing more about their diet could give clues:
Quoting "Implications of a high-energy and low-protein diet on the body composition, fitness, and competitive abilities of black (Ursus americanus) and grizzly (Ursus arctos) bears":
That a 600 lb bear before denning could have less muscle mass than a 500 lb bear in mid summer is definitely true.
The two most extreme populations (fattest and least fat) of brown bears I have seen info on:
Population; mean Spring, Summer, Fall body fat %
GMU13 of Alaska; 9.3%, 5.5%, ~30%
Flathead River Draingage and upper Columbia River drainage males; 21, 33, 37
Flathead River Draingage and upper Columbia River drainage females; 19, 33, 37
a) GMU13 bears increased in body mass by 15% in mid-summer vs spring, matching expectations from the article quoted above about bears eating high protein food mostly building lean body mass. Do note that an earlier study, cited by that one, on captive brown bears found this to be the case (in that study they fed young bears different foods and measured how their body fat and lean body mass changed).
b) "Implications of a high-energy and low-protein diet on the body composition, fitness, and competitive abilities of black (Ursus americanus) and grizzly (Ursus arctos) bears" is the source for the body fat values of those two British Columbia bear populations.
For GMU13 bears:
500 lb summer bear lean body mass: 472.5 lbs
600 lb fall bear lean body mass: 420 lbs
In those two largely herbivorous brown bear populations (in which the bears are on average much smaller than 500 lbs, so perhaps a bit unrealistic):
500 lb summer bear lean body mass: 335lbs
600 lb fall bear lean body mass: 378 lbs
So that is definitely true for some populations, but not true for others.
Also very interesting to note:
To match a 500 lb bear with the average summer body fat % of GMU13 it would take a 705 lb bear with Flathead/Upper Columbia River drainage.
Assuming body fat is of little help in a fight compared to lean body mass, a 500 lb bear from GMU13 could be an even match with bears from some other populations that are 200 lbs heavier during the same time of year!
(If that time of year is summer)
Although, because the average body mass of male grizzlies from Flathead/Upper Columbia drainages was 163.6 kg it would take a bear twice the size of the populations average, and at that point I don't think we can assume it would be otherwise normal as well (so big because it is fat, or so big because it has a different diet higher in protein?).
Strictly hypothetical, but nonetheless interesting to think about.
Either way, it is clear that yes: what you said is definitely something that we should consider heavily.
Not only does it vary a lot depending on time of year, but also within the same time of year when comparing between populations.
Differences can be (but aren't necessarily) much more extreme than even the 500 lb vs 600 lb hypothetical you gave.
I would love to see more research on Ursus arctos lasiotus. How fat are they?
On the one hand they are much larger than the Flathead/Upper Columbia river drainage bears suggesting they may have a higher protein diet to get larger, but on the other hand if that is so the protein must come primarily form plant sources because they are largely herbivorous:
5.1. The composition of feed
The analysis of feces showed that the plant food in the annual diet of animals, accounting for
UT 90%. According to GF Bromley (1965), this figure is lower - 66%. Foods of animal-prois
circulation may also be important. Despite the low content in the second-
Euclidean diet (9%), in different seasons, their share could increase. In April, it was
46%, primarily due to eating the dead bodies of hoofed animals.
Previously published list of edible brown bear of the Sikhote-Alin mountain plants con-
contains 27 species and genera (Bromley, 1965). Based on the definition contained in the go and
feces of brown bear parts of plants supplemented by a list that was 66-Vie
Dov vascular plants. In addition to vascular plants of the brown bear forages are
brown algae, lichen and peltigera fruiting bodies of certain fungi.
In the Sikhote-Alin brown bear eats many invertebrates (oligochaetes,
molluscs, insects) and vertebrate (bony fish, amphibians, reptiles, birds, mammals,
melting) of the animals. Among the invertebrates in the diet of the bear the most important role played by population
komye. Power salmon is not significant for the bear Sikhote-Alin and more
found in the diet of animals that live on the eastern slope of. Meat of mammals
brown bear eats willingly. Most often in the feces were the remains of ungulates (6.2%):
red deer, roe deer, wild boar, musk deer, predators rarely (2.1%): brown and Himalayan bears, a bar-
female, raccoon dogs and tigers. All in all mammals share of the annual accounts for 8.7%
The share of earthy substances (soil, clay, etc.) in the feces of the animals was 1.3%. In
consumption of minerals may occur in the solonetzes (Panichev, 1987).
From here, copy and pasted into google translate.
The Flathead/Upper columbia river drainage bear's % ungulate in the diet was 4%, 0.6%, and 24% during the three waking seasons. Herbs were 60.5%, 5.9%, and 7.2%, while major fruits were 6.2%, 81.3%, and 21.8%. Minor fruits and roots-corms also became important in fall, reaching 13.2% and 28.3% respectively. Grass at 14.2% in spring was also important.
"Implications of..." is again the source (as throughout this post) on that population.
IMO, U. a. lasiotus looks like it is on the herbivore side of things.
I would definitely like more info though.
Regarding Peter's posts (quoted by Panzerdevision):
He has read far more literature regarding brown bear - tiger relations than I have, but I must disagree with some of his opinions and interpretations of translations.
Such as his belief that tigers would have the advantage when both stand on their hind legs and his view of Syseov's story about Amba.
Either way, he is definitely a top quality poster.
Quick note regarding size of GMU13 bears; info posted by Grahhh of ShaggyGod:
He has a long list of tables from captured bears in this region, of which the above is the first. I wont post all of them. An asterisk next to the weight means it is an estimate.
Looking through the tables the largest non-estimated weight I see is 662 lbs for a 10.5 year old male captured on 5/15/84 (who was shot and killed 3 years later).
The largest weight given was an estimated 800 lbs for a 13.5 year old male captured on 5/16/84, who was then shot and killed in September of that year.
I hate hunting.
Still trying to find info on the diet of GMU13 bears. From "Population dynamics and life history trade-offs of moose (Alces alces) in south-central Alaska":
Will have to track down those sources.