Modern weights and measurements on wild tigers

[GuateGojira]

Issues with the Averages:

Creating average figures is a "tricky business". For more that we want to make a reliable figure, there are many factors that affect the results.

For example, I am 100% convinced that the sample that I used did include subadults and/or unhealty specimens. This is because modern scientists that use reliable methods to age tigers shows that many subadults are already of the same size as a adult one but there are still not even at 3 years old. One good example are the tigers from Nepal, one is the subadult male of 216 kg (M-123 I guess, as it was the oldest of the subadult males) and the female F103 plus other 2 subadult females that weighed between 129 to 145 kg. Those are "adult weights" figures, but came from subadult specimens that did not surpassed the 2.8 years old.

We can correct the figures of the male tigers with the records of Cooch Behar and John Hewett because they present the entire list of figures, but we can't do it with Brander as he just presented the average of all. Other thing is the we can't correct the figures from the females, as the overlap between "adult" and "subadult" is complete and all the females are heavier than 100 kg (except for those from the Naga hills, which he "guess" are adults). In the Nepal study, the lightest female was the specimen F108 with a weight of 116 kg, but the female was in really bad shape and died in the process. Other female, F115 - Chuchchi, weighed only 98 kg at her dead but she was emaciated!

Other thing is that Brander himself stated his doubts about the reliability of many "old" weights, check this:

*This image is copyright of its original author

He is right, for example, with the tigers from the Mahratta region, check this:

*This image is copyright of its original author

The weights do not match with the body measurements (chest girth of 130 cm and a weight of only 172.4 kg???), they look like from a differente animal species, like Brander stated. So, how reliable are those old figures? Even the most serious of the naturalist doubted of them.

Apart from the "subadult-adult" issue and the "measurements vs weight" issue stated by Brander, we must take in count the sample size. For example we have only many specimens from one region but very few from others. This create a bias in the sample and if we take the biggest samples are surrogated from the entire population (Central India and Northeast India) is clear that tigers average no less than 200 kg, including subadults. 

So, with this list of problems to create an average figure, how reliable is the information that we can get? Certainly the method used by BoldChamp in other forums (which is getting all the weights availble independently of its reliability, region or source, and puting them in "soup") is the less reliable one. Even I, which tried to divide them in "genetic areas" and create average figures for the regions, using only the figures from verified sources, still have problems with the results. It seems that the ending result will depend of what we use for the average, after all there is a point when the "sample size" is no longer a factor but the reliability and accuracy of the figures used.

Other thing is the methodology, as I am using the average of the averages to get the figures. In this form the average of the 8 population's average figures is 197 kg, but what happen is we use only the single weights? In this case we have 124 single weights that we can use, the only ones that will be excluded are the males from Brander, as I said before he just presented the average of his sample, not his individuals. Using this sample of 124 males, subadults included, the average figure is of 200 kg (range: 97 - 272 kg) and this is also including the Sundarbans tigers!

It seems that at the end, there are many variables that will affect the averages that we will get. Now if we exclude all the males of less than 180 kg (which is the lower figure of males over 3 years old, recorded by scientists, adjusted for stomach content), the average will be 212 kg (n=97, range: 180 - 272 kg) or 214 kg (n=139) including the average of Brander. Including Sundarbans, the average will be 207 kg (single specimens), or 203 kg including Brander (average of averages). I still think that Brander's avearge figure is reliable, because even when he included "gorged" specimens, that inclution of subadults in his sample leveled the average overall. Yes, I know that Brander says that he used "mature" animals, he also says that "the classification of what is a mature animal has presented some difficulty, and would vary according to the views of the individual". So, based in the methods used in the old days, we can conclude that those clasifications are not entirely reliable.


At then end, it depends of what method we use:
* Overall with Sundarbans: 197 kg - n=166 - range: 97 - 272 kg.
* Overall Mainland only: 208 kg - n=160 - range: 150 - 272 kg.
* Single weights with Sundarbans: 200 kg - n=124 - range: 97 - 272 kg.
* Single weights Mainland only: 204 kg - n=118 - range: 150 - 272 kg
* "Adults" only with Sundarbarns - single weights: 207 kg - n=103 - range: 97 - 272 kg.
* "Adults" only with Mainland - single weights: 212 kg kg - n=97 - range: 180 - 272 kg. 
* "Adults" only with Sundarbarns - average of averages: 203 kg - n=145 - range: 97 - 272 kg.
* "Adults" only with Mainland - average of averages: 214 kg kg - n=139 - range: 180 - 272 kg.

An average figure of all these results will be of 206 kg, which will cover all the posibilities, but if you ask me, personally I think that a figure of about 200 kg is correct for the Bengal tiger IF we include Sundarbans and the subadult and/or postprime specimens, or about 210 kg for mainland males, also including subadults. The same treatment should be make for females. Reply