Estimating Male size based off the Female

[Pckts]

Most of you may have seen the great work @tigerluver is doing, estimating male tiger size based off females so I figured that I'd move all of them here and continue the discussion.

So far

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Tigerluver writes "A while ago, I took the length of the two from the picture and estimated that Amur male by isometry. From the photo, he is 1.17x longer, which equates to 1.6x in weight. Taking the 115 kg average for Amur female in STP, the estimate would be 185 kg for that male. "

"the Amur in that photo has chest diameter 1.23x the female, translating to 1.86x the mass and 214 kg with the 115 kg number for the female. Averaging length and chest diameter gives 200 kg for the male, which I guess would be a large Amur male based on what we have now. "

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2 year old Pandit and mother, Sharmili.

Tigerluver "Lengthwise, he's 1.18x length without correcting for perspective and angle. Maybe 1.13 would be a corrected value.

In terms of chest diameter, the son 1.20x his mother's size with correction. Perhaps 1.15x can be the number to put here to deal with perspective.

Same methods as above result in a length estimate of 188 kg, chest estimate of 198 kg, averaging 193 kg. "

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A very young saturn with his female from Tadoba

Tigerluver "I split the image and straightened the tigers.

He's 1.12x her length and 1.20x her chest diameter. 


Length based estimate (if female is 130 kg) is 183 kg and chest diameter estimate (again assuming the female is 130 kg) is 225 kg, averaging 204 kg. "

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The Duisburg Zoo male Amur tiger

Tigerluver "I measured the female to be around 160 cm, which seems like a ~115 kg female basing off the slightly shorter female Jasmin and the STP tigresses. So the male is 1.31x the female's length and 1.32x the female's chest girth from examining the photo.

If I were to estimate the Duisburg male based on this female, we get:

Length based: 1.31^3 * 115 kg = 260 kg
Chest diameter based: 1.32^3 * 115 kg = 265 kg
 
Now with his body length I can apply some estimates from data of other male tigers.

Based on the STP males, isometrically scaling his 210 cm frame based on the average of 7 males of the study (avg. body length = 196 cm, avg. mass = 182 kg), he would weigh 224 kg. An issue with using the STP males is that the wild Amur seems have lost a lot of the robusticity found in captive Amurs and the rest of the tiger subspecies. In other words, STP males are very lanky compared to their captive Amur cousins, and the Duisburg male would likely be more like other captives Amurs rather than the wild STP males. The Duisburg male is also taller proportionately than the STP males.

To account for height in the equation, I used the following data. 6 STP males averaged 94 cm at the shoulder and weighed 184 kg. Isometrically estimating Mr. Duisburg from these numbers and his 110 cm height results in a mass of 295 kg. This somewhat accounts for the underestimation by the body length estimate. Combining both body length and height estimates gives a mass of 260 kg. Coincidentally on par with the estimate based on the female by his side. 

Based on some captive Amurs, the mass values are bit higher. Looking off the table @GuateGojira provided in the Amur tiger thread and the three males of Christiansen, I came up with a average body length and weight for captive Amurs where were as follows:

n = 6
Body length = 195 cm
Mass = 223 kg


Isometrically scaling the Duisburg male from these figures results in a mass of about 280 kg.

Had he had Bengal tiger proportions, he would likely be heavier and significantly so at 280-320 kg. Comparing him to Sauraha for example, shows a body length with the potential to harbor a 320 kg cat. The problems I see with using Bengal tigers for comparisons is that the Duisburg male for one, does not seem as bulky as Bengal tigers and the fact that he still is an Amur in the end, and would likely keep to their somewhat leaner built. 

I have to revisit the photos, however. In the latter two photos the Duisburg males look bulkier than the first photo. Measuring the chest diameter/body length ratio, he is at least 5% less bulky in the photo with the female than in the photos he was alone. Bulking him up in the photo analysis and comparing him with the female gives a chest diameter mass of 306 kg. Averaging this value with his presumably constant body length then gives an average mass of 283 kg.

All in all, isometry based on Amurs gave me a mass range of 260-280 kg for the the Duisburg male.

(I tried a new method of creating clear subtopics without needing subheading by bolding the first few words of the new subtopic. I hope it made the read easier.) "

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T25 with female T19, said to be larger than her sister, T18 (weighed 170kg)

Tigerluver "First what is on the plain of the image (no adjustments). T25 is 1.085x longer and 1.093x larger in chest diameter.

In terms of correction, T25 has his head more tucked in, so from the plain of the image one could say he is 1.09x longer.

Now in terms of perspective, T25 is further back than T17. I think compensating by increasing the length difference to 1.11x and girth difference to 1.113x would be okay, maybe a bit too conservative but we'll stick with this for the first set of calculations.

So to estimate mass:
Length based mass = 1.11^3 * 170 kg = 233 kg
Chest based mass = 1.113^3 * 170 kg = 234 kg
Both values are functionally the same.

Now a caveat is that if you look at how much difference being even a meter behind another object will shrink the object further back, the aforementioned compensation is likely too little. Maybe compensating both difference ratios to 1.13x-1.15x would be more accurate, which is a mass of 245-260 kg, similar to T24. "

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Kingfisher and Umarjhola Female from Kahna

tigerluver "Top photo:
Without correcting anything for perspective:
The male is 1.08x the length of the female but the male is at a shortening angle.
His chest diameter is 1.41x that of the female's, however.

Bottom photo:
Male's length in this one is 1.40x the female's, but the female is at a shortening angle.
Male's chest girth is 1.37x that of the female's.

Not exactly sure how much to compensate for the male being closer in the photo. Perhaps the male is 1.10x the female's length (average the two photos and deduct for his positioning) and the his girth is 1.25x the female's with the same compensations. 

So say the female is 130 kg, isometry results in:
Length based: 1.10^3 * 130 kg = 173 kg
Chest diameter: 1.25^3 * 130 kg = 254 kg
Avg. = 214 kg

If I compensated the male too much, we could say 1.15x length (198 kg) and 1.3x girth (286 kg) at best, which using the above method would come to 242 kg. I'd put this number as the high end and would prefer the more conservative numbers above. All in all, the male is stockier than the female but not much longer. "





This is what we have so far, I'll continue to post what I can find and hopefully we can use this technique more often.
My other thought would be if there is any correlation for limb girth or shoulder height to body weight.

Once again, GREAT WORK @tigerluver Reply