It is slightly pointless to work out the average weight of a mountain lion because the weight of adult mountain lions varies considerably over their huge geographical range. The mountain lions from the most northern range (Canada) and the most southerly areas (Chile) of its distribution are twice the weight of mountain lions living in the tropics (in the middle areas of its distribution). The smallest are found in the equatorial tropics of the Americas – Central America and the north of S. America.
Adult male mountain lions from Peru have been recorded as weighing 28-30 kilograms (30 kg is 66 pounds). In contrast adult males in Canada and Chile weigh 65-85 kilograms (85 kilograms is 187 pounds).
Adult males weight about 40-60% more than females.
The size of the mountain lion is frequently overestimated. A giant mountain lion reported in Sports Afield Hunting Annual weighed 170 kg (375 pounds). The cat was killed in the Chaco region of Paraguay in 1958. An Arizona mountain lion killed in 1917 weighed 125 kilograms (276 pounds) with intestines removed. The weight was certified as true to the US Biological Survey.
As for an average weight, National Geographic state that the cat weighs 62 kilograms or 136 pounds. They don’t specify the gender. I presume it is male. Wikipedia state: 62 kg for adult male (137 pounds) and 42 kg for adult female (93 pounds).
The most definitive work on the wild cats, The Wild Cats Of The World by the Sunquists does not try and specify an average weight across the entire distribution because as stated above it is rather valueless.
For comparison the average weight for a UK woman is 147 pounds, ten pounds heavier than the average male mountain lion weight.
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