the cougar in the santa ana mountain range, california

may be typical of, or only moderately less than,
truit of other populations. Three of the 4
previously published rates provided
unrealistically high estimates of true survival
rates. Comparing mean litter sizes near birth
and at 12 months (not the same litters followed
through time) Ashman et al. (1983), suggested
a value of78%. Similar data in Robinette et al.
(1961 :213, inferring age from weight)
suggested a survival rate of about 73%.
However this method considers only litters in
which at least I cub survived to 12 months of
age. Whenever all cubs in a litter died within
12 months, the method would not detect a litter,
thus ignoring a large number of cub deaths
(Robinette et al 1961:213). Hemker et al.
(1986) followed marked animals over time,
reporting a survival rate of 72% for cubs
between 3 and 10 months of age and 92% for
cubs from 10 months to dispersal at 16-19
months, in an area of extremely low cougar
density (gross density of 0.5 cougars per 100
km 2 ). Hemker et al. (1986:330) cautioned that
their estimates did not reflect overall juvenile
survivorship because they excluded the 2
periods of highest mortality, namely the early
neonatal period (age 0-3 months) and the postdispersal
period. Their estimates also may
reflect density-dependent enhancement of
survival rates at low density. Using methods
similar to ours, Anderson et al. (1992)
computed the survival rate for yearling cougars
as 0.642, an estimate much closer to ours than
the previous reports; they did not attempt to
monitor or estimate density for juveniles less
than 1 year old.
, In many cases, we could infer cause of
death ofjuveniles (Table 4). Vehicle accidents
and being orphaned were the leading causes of
death for juvenile cougars (5 cases each).
Cougar-inflicted injuries were implicated in 3
deaths. These cases are discussed in greater
detail in later sections of this chapter. In most
other cases, the cause of death could not be
determined.
42
Adult survivorship
Adult survivorship was computed from
data on 20 adults monitored for periods oftime
varying from 2 to 58 months, or a total of 497
cougar-months. There were insufficient data to
compute survival rates separately for males and
. females, and our sample was mostly females.
We analyzed these data using I-month time
intervals and the product limit procedure with
staggered entry (Pollock et al. 1989). The
product of 12 monthly rates yielded an estimate
ofannual survival rate, and the average ofthese
running products yielded a single point
estimate.
The annual survival rate for adults was
75%. This means that on average an adult had
a 75% chance of being alive in 12 months. F7
and FlO were dropped from the computations
in the month we lost their signal. If these
animals in fact died at the time of
disappearance (which is probably true for FlO
at least), then the adult survival rate was 72%.
As with juveniles, vehicle accidents were the
leading cause of death (Table 5), killing 5
adults (F8, F9, FI2, F13, FI5). Two adult
cougars (Fl, F6) were killed by other cougars.
Two (F2, F3) died of intestinal illnesses
(probably not the same disease). Three adults
(M1, M2, F II) were shot on depredation
permits after eating goats or sheep. Two
cougars (F7, FlO) disappeared abruptly; there
is some evidence that FlO may have been
poached. Each cause of death is considered in
greater detail in the following sections.
Our estimated adult survival rate of
75% is higher than the approximately 68%
inferred from hunting returns of marked
animals by Ashman et al. (1983) and from
existing age structure by Robinette et al.
1977: 123). Our estimate is nearly identical to
the 74% observed in Utah by Lindzey et al.
(1988), and somewhat lower than the
approximately 80-92% observed in Colorado