ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)

[peter]

(01-05-2019, 07:37 AM)Shadow Wrote:

(01-04-2019, 08:47 PM)peter Wrote:

(01-04-2019, 09:05 AM)Wolverine Wrote: Reason for scavenging of wolf kills by brown bears which probably could be applied for the brown bears and tigers as well:

"Additionally, grizzly bears now take advantage of the predatory behavior of wolves by waiting for the wolves to finish hunting and then contesting the wolves for access to the carcasses of their kill (Smith et al., 2003). As a result of being the larger animal in these standoffs, bears usually win, giving them access to food without the work involved in actually tracking down and killing the prey themselves (Smith et al., 2003). In addition to the obvious benefit of being able to consume this food, the grizzly bear populations do not have to expend the energy to hunt, as they now have a species that virtually does the hunting for them (Smith et al., 2003)."

https://www.lakeforest.edu/live/news/5515-impact-of-wolf-reintroduction-on-bison-and-grizzly?preview=1

Yes, read that one some years ago. It's no doubt true regarding brown bears and wolves in the northern part of the Americas. Same for bears and pumas. There is, however, a difference between wolves, pumas and tigers.

AUTHORITIES ON BEARS AND TIGERS IN THE RUSSIAN FAR EAST- RECENT PAST (1900-2010)
 
Over the years, I've read quite a bit on tigers and bears in the Russian Far East. Most authorities agreed that large bears displaced tigers more or less at will (1). Although they admitted that tigers hunt more bears than the other way round, that mainly was a result of tigers deciding when to hunt what bears where (2). Tigers, of course, decided for cubs most of the time (3). If they took a largish bear, it was a result of an ambush (4). In a one-on-one in non-ambush conditions, bears, if of similar size, would previal more often than not (5). Even large females came at quite a cost (6). Tigers disputing authorities, of course, often paid. No less than 12 perished in fights with bears over the years (7). All in all, they agreed that bears were 'too dangerous' to hunt for tigers (8). Etc.

I'm not saying large bears would be unable to displace male tigers. I'm also not saying that tigers and bears is a one-sided affair. Recent research, however, says it's about time to redefine a few statements that survived the ages.

TIGERS AND BEARS IN THE SICHOTE-ALIN NATURE RESERVE 1992-2013  - DISPLACEMENT

A few weeks ago, an interesting document ('Interspecific Relationsships Between the Amur Tiger (Panthera tigris altaica and the Brown Bear (Ursus arctos) and Asiatic Black Bears (Ursus thibetanus', Seryodkin et al., 2017) was discussed in this thread.

In the period 1992-2013, researchers found 763 animals eaten by tigers. Of these, 378 were eaten in the period that bears were not hibernating. In 11 of these 378 cases (2,91%), tigers were displaced, whereas bear and tiger shared in 7 cases (1,85%). Tigers lost, or partly lost, 4,76% of their kills to bears. Less than 1 in 20, that is.      

In the 11 cases of displacement (in one of them an adult male Himalayan black bear was involved), bears displaced tigresses (in one case, the gender of the tiger was unknown). Of the 7 tigers forced to share their kill with bears, 1 was an adult male tiger. 

All in all, we're talking about 18 cases in which tigers were displaced by bears or forced to share in the period 1992-2013. Less than once a year. And 'tigers' turned out to be tigresses in nearly all cases.

TIGERS AND BEARS IN THE SICHOTE-ALIN NATURE RESERVE 1992-2013 - TIGERS HUNTING BEARS

In the period 1992-2013, 8 Himalayan black bears and 9 brown bears were eaten by tigers. Of the 9 brown bears, 2 (an adult male and an adult female) were not killed by tigers. Of the other 7, two ranged between 1-4 years of age. The others were adult females. Of the 8 Himalayan black bears, 2 were young adults. The others (males and females) were adult.

Tigers killed less than 1 bear a year in the Sichote-Alin Nature Reserve in the period 1992-2013, that is. Of the 15 they killed themselves, 2 (brown bears) were immature. All others were adults.

Which tigers hunt bears? Of the 15 bears killed by 'tigers', 8 were killed by adult male tigers. The other 7, therefore, most probably were killed by adult tigresses.   

TIGERS AND BEARS IN 3 SITES IN THE RUSSIAN FAR EAST - TIGERS HUNTING BEARS 

Of the 378 animals eaten (and most probably killed) by tigers in the period that bears were available, 15 (3,97%) were bears (both species).  In the Sichote-Alin Nature reserve, the conclusion is that tigers are modest bear hunters.

According to Kerley et al. ('A Comparison of Food Habits of Amur Tiger (Panthera tigris altaica, Temminck, 1844) at three sites in the Russian Far East', 2015), bears are more often hunted in the south of Sichote-Alin. Corrected for pseudo-replication, the percentages are quite high:

*This image is copyright of its original author

Remember that the percentages refer to biomass, not the number of animals killed by tigers. Also remember that most bears were hunted in summer, not winter.

Here's the map in the article of Kerley et al. There is some confusion about the location of the Sichote-Alin Nature Reserve. It's the reserve in the northeastern part of Sichote-Alin (no. 1 on the map below). In the map, that reserve is the Southwest Primorskii Krai (SW). 

My guess is a mistake was made. Same for the percentages in that 1 was 3 and the other way round:  

*This image is copyright of its original author

 

CONCLUSIONS

The info in this post is without the observations of K.N. Tkatchenko ('Peculiarities of nutrition of the Amur tiger Panthera tigris altaica (Carnivora, Felidae) in a densely populated locality (on the example of the Bolshekhtsirsky reserve and its environs'), 2012). The tigers he studied in the northwestern part of Sichote-Alin were heavily involved in bears.

Based on these 3 studies published in 2012, 2015 and 2017, we can get to a number of conclusions. One could say that each of them debunks an assumption close to a myth and be close.  

01 - Although tigers in the Russian Far East are wild boar hunters foremost, bears are an important food source. Biomasswise, bears are as important as wild boars in some regions.

02 - Most bears are not hunted in winter, as many assume, but in summer. 

03 - Tigers in the Sichote-Alin Nature Reserve (situated close to the coast) are modest bear hunters: about 4% of all animals killed in the period 1992-2013 are bears. In reserves in the northwestern, southeastern and southwestern part of Sichote-Alin, the percentages are (significantly) higher.  

04 - In the Sichote-Alin Nature Reserve, brown bear cubs (< 1 year of age) were not hunted in the period 1992-2013. Two of the 7 brown bears killed ranged between 2-4 years of age. The other 5 were adult females, averaging 140-150 kg. Of the 9 Himalayan black bears killed, 2 were young adults. The other 7 were adult. Of the 15 bears killed (both species), 11 were adult, whereas two (Himalayan black bears) were young adults. One of the two immature brown bears killed a was 3-4 year old male. Based on the info I have on the size of immature male brown bears, the bear could have been as heavy as his killer, if not heavier.  

05 - Many assume that bears, and brown bears in particular, are hunted by adult male tigers only. In the Sichote-Alin Nature Reserve, however, 8 of the 15 bears hunted in the period 1992-2013 were killed by adult male tigers. The other 7 bears were killed by young adult male tigers or adult tigresses, that is.

06 - In the Sichote-Alin Nature Reserve, tigers killed 378 animals in the period bears were not hibernating. Bears displaced tigers in 11 cases (2,91%). In 7 cases (1,85%), tiger and bear shared the kill. Tigers lost, or partly lost, less than 5% of their kills to bears, that is. Less than 1 in 20. This in a period of 21-22 years. And 'tigers' turned out to be tigresses in all but one case (in which an adult male tiger shared his kill with a brown bear).

07 - In the Sichote-Alin Nature Reserve, no tigers were killed by bears in the period 1992-2013.

08 - Based on 1-7, one can't, as some did, conclude that (brown) bears are 'too dangerous' to hunt. Tigers avoid adult male brown bears, but adult females " ... up to the largest and healthiest individuals ... " (Kerley, 2011) are hunted more often than many apparently assume.

Kerley's observation is supported by those of Bart Schleyer, who followed tigers in the snow. Most of them were older males, who had about a hundred pounds on the bears they followed. All bears were killed and all were killed with a bite to the base of the skull.

Recent observations suggest that the largest female brown bears killed by male tigers ranged between 150-200 kg. One of the male tigers was injured during the fight.  

09 - According to those who know, adult males of both species avoid each other. Although most favor the bear in a fight, male tigers were not displaced by brown bears in the Sichote-Alin Nature Reserve in the period 1992-2013. 

10 - In recent articles, researchers said 12 tigers have been killed by brown bears in fights. In 10, adult tigresses and youngish male tigers (adolescents and young adults) were involved. I know of two cases in which adult male tigers were killed by bears. The tiger killed in 1960 was a young adult male. That incident was described more than once. There's no info about the tiger killed in 1972.

Peter, your posting 1 870 with report: Interspecific relationships between the Amur tiger (Panthera tigris altaica) and the brown (Ursus arctos) and Asiatic black bears (Ursus thibetanus) - I

In your posting isn´t at all page 3/10. You have there 2/10 and next is 4/10. That is the reason you seem to miss some information. I translated whole original document with google translator and there is more about those cases in original document, than there is in that which you have.

And I also think, that when we have open cases, we can´t assume automatically, that female tigers killed those bears. We simply don´t know what happened, when researchers don´t know either.

Your response to my last post was the reason I read the article again. When I noticed that page 3 was missing, I logged in to inform you. But you beat me to it. Excellent reading and many thanks!  

Why such a basic error? As a result of the amount of info on tigers and bears published in the last years, I decided to reorganize the entire administration. Everything I have is on my table and it's a lot. Page 3 no doubt is somewhere, but I would appreciate you posting the page as I'm very busy at the moment. Thanks in advance.

I don't know if the situation in the Sichote-Alin Nature Reserve is typical for all reserves in the Russian Far East, but if we assume it could be, the conclusion is that about 80% of all bears killed is killed by male tigers (12 out of 15). If we know the number of bears killed by male tigers, we have to add 25% to find the total number of bears killed by tigers.

When we want to find out how many bears (both species) are killed by tigers every year, we need to start with the number of male tigers. Not all of them hunt bears. Based on the info from the Sichote-Alin Nature Reserve, it's likely that some of them are specialists. This is what Tkatchenko (2012) found in the reserve in the northern part of Sichote-Alin and the situation in the Sichote-Alin Nature Reserve seems to be similar in this respect. My guess is it isn't very different in tigresses, as it takes a lot of skill to hunt a bear.  

In the Sichote-Alin Nature Reserve, tigers hunt quite large bears. The table in the article of Kerley et al. (2015) I posted says tigers hunt bears more often in the southern part of Sichote-Alin. Based on the info provided by Olga, tigers kill quite many young bears in the south. So much so, that female brown bears left districts with experienced bear hunters. This means that the average weight of bears killed in the southern part of Sichote-Alin most probably is lower than in the Sichote-Alin Nature Reserve. Biomasswise, however, bears still are an important source of food in the south. More so than in the Sichote-Alin Nature Reserve. This most probably means they not only hunt cubs, but larger bears as well. 

Although it's likely that tigers kill a few hundred bears every year in the Russian Far East, the effect of predation, percentagewise, most probably is very limited. The reason is the number of bears in regions inhabited by tigers. In some districts in the southern part of Sichote-Alin, however, the pressure could be relatively heavy. Reply