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

[peter]

TIGERS IN NORTHERN INDIA AND NEPAL - PART VII 


a - Cooch Behar, the Duars and Assam (tigresses)

Most of those interested in morphology read the book written by the Maharajah of Cooch Behar ('Thirty-seven years of big game shooting in Cooch Behar, the Duars, and Assam. A rough diary. ', Bombay, 1908). I think it is appropiate to start with the information presented in this book, as it most probably still is the most detailed and most reliable set of data. The Maharajah told us in what way the tigers shot were measured. In contrast to many others, he also provided information on body dimensions and weight.

Those who read his book often debated about their findings on forums. Although they were close regarding the results, they didn't agree in all respects. One of the reasons is the classified information was lacking. This post has a table with all tigresses shot. It should allow all interested to get to solid conclusions.  


b - The table (individuals)

Although a few tigresses well surpassed 9 feet 'over curves', the short tigresses (no. 13, 19, 27 and 35) were as remarkable. Tigress no. 27 was 8 inches shorter than the next shortest (no. 35). Although I found the locality, I don't know if it was in Cooch Behar, the Duars or Assam. Maybe you can find out more. This tigress measured 'over curves' was shorter than some male leopards measured 'between pegs'.

The Maharajah wrote that tigers shot in this district " ... run generally small, although there are some big ones amongst them ... '' (pp. 294). Remember this was in a part of India where tigers often exceeded the average for India (all regions except the Sunderbans and the Naga Hills) in both length and bulk.

On forums extra-large tigers often are discussed, but small ones are as interesting. Over the years, I noticed that extra-short tigers and tigresses were measured everywhere in India. As there was no question that they were adult, the question is why they were so much shorter. Individual variation or was there something else?

I didn't find an answer, but did notice that short tigers were more often seen in regions located at the edges (the southern, northern and eastern tips of India). Assam, although known for very large individuals, also produced a significant number of extra-short tigers, especially in the southeastern part. One explanation is the Naga Hills are not that far away. As male tigers in particular are known to cover great distances at times, it is likely some Naga Hills tigers reached adjacent regions like Assam.

I noticed similar things in other parts of Asia. In some hot spots (good conditions and many large prey animals), tigers reached a large size. A century ago, Annam (Vietnam) produced males similar in size to those in India or even larger. This was one of the reasons American hunters selected Vietnam and not India in the twenties and thirties of the last century. In less attractive districts (denser vegetation, more precipitation and less large prey animals) not that far away, tigers often were much smaller.

Anyhow. The information from Cooch Behar, the Duars and Assam shows that hunting also had an effect on the average size of tigers over time. I dont think it was a result of selection, as it wasn't easy to contact experienced large tigers when the amount of time available was limited. The most likely reason hunting had an effect over time, was limited numbers. Apex predators never are plentiful. When you remove male tigers that made it to adulthood and a territory (generally more visible than those who didn't), you remove the genes of success. The result is those not tested (young adults) and those unable to get to a territory (smaller animals in most cases) will get a chance to breed. Over time, this will have an effect.

Remember this process works different in males and females. In males, the results of removing adults with a territory will be more pronounced than in females because of the nature of the selection system (sexual drive). In spite of that, hunting has an effect on the average size of tigresses over time (two decades only) as well.

Table I:      
               

*This image is copyright of its original author

 


c - Averages

This is the table with the averages. It is based on the table above. I will compare them to the averages in other regions in a few days. For now, we can say that tigresses in northeast India, at just over 8.9 in total length 'over curves' and 310-311 pounds, were quite heavy for their length.

Table II: 

*This image is copyright of its original author

Now that we know a bit more about the average total length 'over curves', what to say about the total length 'between pegs'? 

Only one tigress was measured both 'over curves' and 'between pegs'. This tigress (no. 24) was a bit longer than average (just over 9 feet as opposed to just over 8.9 for all). She was 4,75 inches (12,06 cm.) longer when she was measured 'over curves'. As the difference between both methods usually increases with length and most tigresses were a bit shorter, I would suggest 4-4,5 inches (10,16 - 11,43 cm.) for all tigresses for now.

This means tigresses in northeastern India most probably averaged 255-257 cm. (8.45-8.55) 'between pegs' in total length a century ago. A tad longer than tigresses shot in the Central Provinces (Dunbar Brander, 1923), that is. They were, however, heavier and this, as will be seen later, is also true for males; a century ago, tigers in northeastern India, compared to those shot in the Central Provinces, were similar in total length, but heavier.

Remember that the difference between both methods in northeastern India could have been more pronounced than in northern India. Hewett (2008 reprint, pp. 68 and 70), who had plenty of experience, wrote the difference between both methods in northern India was 2-5 inches in adult tigers (males and females). The reason is the method ('over curves') was applied in a more strict way in northern India. This means that an 8.9 tigress in northern India could have been a bit longer than an 8.9 tigress in northeastern India (both measured 'over curves'). A remarkable conclusion, but it a result of the nature of the method used and the way it was (and is) applied.  


d - About measurements taken 'over curves'
 
Today's biologists measure big cats 'over curves'. Although it was described as a 'standard method' by Ullas Karanth (2001, pp. 47), different biologists, when asked about the details, offered slightly different explanations. Based on the mails I read, I concluded the 'standard method' could be applied in a strict way in Russia and in a slightly different way in Nepal. This opinion, of course, largely depends on the definition of 'strict'. Miquelle wrote the tape is pressed to the body at all points, whereas Sunquist opted for less curves and more straight lines in Nepal. I'm not sure about Nagarahole (Karanth didn't respond to questions), but Sunquist was there when a few tigers were measured and he apparently didn't see any differences with the method he applied in Nepal.   

Karanth wrote that " ... tigers captured for radiotelemetry studies in Nagarahole (India), Chitwan (Nepal) and in Sichote-Alin (Russia) ... are all about the same size ... (2001, pp. 48). We also know that if the method used to measure tigers ('over curves') is used in a strict way, the difference between a measurement taken in that way and a measurement taken 'between pegs', in theory, should be limited to 2-5 inches (Hewett, the 2008 reprint, pp. 68 and 70). When tigers in the regions mentioned above really are similar in size, this, in theory, should result in slightly lower averages in the region where the method is used in a strict way. 

Not so. Nepal tigers, although they were nearly measured 'between pegs' (according to Sunquist), were a trifle longer than tigers in Russia. 

So what is going on here? Are Nepal tigers longer than Amur tigers? Should we perhaps redefine 'strict'? Maybe the explanations offered by the biologists contacted were a bit incomplete? Or could it be that the 'standard method' just isn't easy to explain?

I really wouldn't know the answers to the questions, but it seems best to deduct 3-4 inches for males in Nepal and a bit more in Russia for now. Maybe tigers in Russia really are a bit shorter than those in Nepal, but maybe the samples are just too small to get to reliable conclusions anywhere. And if Nepal tigers are a bit longer, than why is it that captive Amur tigers are the largest captive big cats? 
 
Anyhow. If we deduct 3-4 inches for males in Nepal, the averages of tigers measured 'over curves', then and now, nearly perfectly match those of tigers measured 'between pegs'. Same for northern India and Nagarahole. I'm not sure about Russia, though. The reason is a lack of data (most historical data are considered unreliable). It is, however, acknowledged by all authorities that Amur tigers severely suffered from the bottleneck in the twenties, thirties and forties of the last century, when they were down to 30-50 individuals. Amur tigers really walked the edge. We also have to remember they, in contrast to those in India and Nepal, suffer from habitat destruction and prey depletion. You are what you eat. If you eat smallish to moderate amounts and have to work harder for it in conditions described as 'tough', chances are you will lose weight. And, perhaps, length. To a degree, as long bodies are needed to survive the Russian winters.        
    
What I'm saying is it seems best to stay away from firm statements on size when tigers have been measured 'over curves' for the reasons mentioned above. Every sample has to be treated as a specific case and one has to be careful when comparing regions. It really depends on the quality of the information offered by the one who measured them. Large samples also help. 


e - Cooch behar, the Duars and Assam
 
Based on what I read, I concluded that the information offered by the Maharajah of Cooch Behar is accurate and reliable. As 11 tigers were measured both 'over curves' and 'between pegs' (1 female and 10 males), we also are able to get to a decent guesstimate about the length of tigers in a straight line. This allows for a comparison between tigers shot in northeastern India and tigers shot in the Central Provinces, where they were measured 'between pegs'.    

I do not doubt there was a bit of selection at the gate (most details are from quite large animals), but it is a fact that both samples had extra-short tigers and lacked extra-large animals. Some tigers were gorged, but others were completely empty. Some were old, whereas others most probably were young adults. One can never be sure, but my guess is both samples could have been representative. They also were quite large. As for the tigers shot and not mentioned in the book. I guess quite many were immature. In those days, they not seldom shot anything that moved. 
 
All in all, the information on size is quite staggering. I never saw anything that compared. Dismissing it out of hand, as many biologists apparently do, is a bit too easy for my taste. It also is strange when it is known that they measure tigers in the same way. I leave that one up to you. Reply