70 Percent Females - Best Frat Party Ever!
Wake Up, South Dakota

by MLF staff member Amy Rodrigues


In South Dakota Game, Fish & Parks' (SDGF&P) proposed 2010-2015 Mountain Lion Management Plan, their population estimate is based largely on the assumption that 70 percent of the adult mountain lion population is female. 

Upon reviewing their data and cited references, the 70 percent female estimate appears to be based off data from only two specific examples . . . the first of which is their own combined harvest (hunting) data for 2007 and 2009. 

 

Females

Males

Total

% Females

2007

16

3

19

84%

2009

15

11

26

58%

Average

15.5

7

22.5

69%



During these two years, 31 females and 14 males were reported killed (45 total).  The 31 females represent about 70 percent of the total harvest (31/45 = 68.9%), so SDGF&P made an intuitive leap and now assumes 70 percent of the entire population must also be female. 

They back this assumption up by citing Logan & Sweanor's research from a population study in New Mexico.  Logan & Sweanor's actual study found that the ratio of males to females was always close to 1:1 (equal males and females).  There was one exception however, where they found a case of 70 percent female kittens.  Some of their data suggested young females are more likely to give birth to a higher percent of female cubs during their very first pregnancy only.  Their publication goes on to say, "A closer look at our data indicated sex ratio was female biased in the first litters, but more males were born in subsequent litters. [...]  In eight first litters, there were eight male and nineteen female cubs."  This one line, from one study, is what SDGF&P used to claim 70 percent of all mountain lions in South Dakota are female.

As for the sex ratio of adult mountain lions, yes, Logan & Sweanor found their population sometimes had slightly more females than males because males have a higher mortality rate.  Males require more territory than females and will kill each other for home ranges.  Males also kill each other through competition for breeding females.  If there is one female per male, but some females are "off the market" because they're pregnant or raising kittens, males are now competing over the smaller pool of available females.  However, Logan & Sweanor still concluded "none of the annual comparisons of adult sex ratios in either area were significantly different from 1:1."  On average, the most they saw was a 60/40 female to male split.  They also found that males tend to live longer than females on average.

South Dakota's mountain lion population assumption that 70 percent of all lions are female is only valid if female lions are barely living long enough to breed just once.  This would be like a human population where no one survives past the age of 20.  If this 70 percent female claim is actually true, it would indicate a tremendously high mortality rate and overall decline in the state's mountain lion population.  Why didn't this raise a red flag with their "expert" biologists?

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