Nutritional Ecol ogy of Mountain Lions 83tribute young to the population. Furthermore, one female lost her litter to infanticide
during summer, only to become pregnant again and give birth to a litter in Decem-
ber, indicating that females could obtain sufficient food to regain fat reserves, become
pregnant, and then give birth about 94 days later (a relatively short period of time for
a large mammal).
Mountain lions are considered stalking predators. To maximize their chances of
success when attempting to capture prey, they take advantage of thick vegetation as
hiding cover, or they may attack from up- slope of prey to gain an advantage when a
quick sprint is needed to successfully capture and kill prey (Fecske 2003). Lions have
low endurance relative to chases, so prey that can run fast and long likely will evade
capture. As with any predator, most attempts at capture fail, but as animals learn
the habits of their prey, they can improve their chances of success. Thus, older moun-
tain lions likely have higher success rates than subadults. Fat stores might be a good
indicator of predator success because when less energy is required for stalking and
capturing prey, the fat can be stored for later use.
When we first began necropsying mountain lions, we used a simple ranking sys-
tem of low, medium, and high to assess fat reserves. Lions classed as having low fat
had little to no fat around the kidneys and virtually no mesentery fat (abdominal fat
associated with the exterior of the stomach and intestines). Carcasses classed as having
medium fat had some kidney fat (the kidneys could be viewed with some exterior fat
and there was some mesentery fat) (fig. 6.4). Those lions classed as having high fat
exhibited extensive fat encasing the kidneys to the extent that they could be completely
covered and difficult to locate, and mesentery fat was extensive.
In addition to ranks, we collected data on both Riney (1955) and total kidney fat
indices (Fin ger, Brisbin, and Smith 1981), which have been used to evaluate the nu-
tritional condition of white- tailed deer (Kie, White, and Drawe 1983; Jenks and Leslie
2003, 2011) as well as other large cervids. These indices are based on the amount of
fat immediate to the kidney (Riney kidney fat index [RKFI]; see Riney 1955) plus fat
associated with the kidneys but extending beyond the perpendicular ends of the
organ (total kidney fat index [TKFI]; see Fin ger, Brisbin, and Smith 1981). These tech-
niques involve weighing fat and kidneys; Riney and total kidney fat weights were di-
vided by the weight of the kidneys (multiplied by 100). As expected, the fat indices
were highly correlated (r^2 = 0.61) with each other (fig. 6.5) and were similar between
males and females (P = 0.47); estimates of RKFI and TKFI averaged 54.7% and 127.4%
for females and 70.9% and 148.5% for males, respectively.
In de pen dent analyses also provided support that these values were stable relative
to sex and age ( table 6.1), although we did document a year effect, which supported
use of the technique for evaluating population- level changes that were potentially re-
lated to change in population size. The change in fat levels through time also supported
our hypothesis that population saturation (i.e., capacity of the Black Hills to support
mountain lions) occurred around and after 2005 ( table 6.1). These first estimates of fat