Biology
Reproductive Season:
(W) Largely aseasonal (Bertram 1975b), but weak (Feb-Apr: Smuts
et al. 1978) and strong (Mar-Jul: Packer et al. 1990) birth peaks
recorded in Kruger and Serengeti National Parks
Estrus (W): 4 days
Interestrus Interval (W): 16 days (Packer and Pusey 1982).
Gestation (C): mean 110 days (range 100-114; n=51) (Cooper 1942)
Litter Size:
(W) from field counts of small cubs < 1 year of age, average 2.5 (n=59,
Serengeti NP: Bertram 1975b) -- 3.02 (n=47, Kruger NP: Smuts et al.
1978); range 1-6, but 98% of litters are 1-4 (n=274, Serengeti NP: Packer
and Pusey 1987)
Interbirth Interval:
(W) mean 20 months (range 11-25; n=38) if previous litter survives to
maturity (12 months); 4-6 months if previous litter lost (Pusey and Packer
1987)
Age at Dispersal:
(W) Males generally leave their natal pride at between 2-4 years (Schaller
1972, Bertram 1975a, Pusey and Packer 1987), but young males may be forced out
much earlier by a pride takeover, e.g. 13-20 months (Hanby and Bygott 1987).
Most young females are incorporated into their natal prides, but about 33% disperse
to form new prides in the Serengeti (Pusey and Packer 1987) -- the percentage
of dispersers may be higher elsewhere (D. Joubert in litt. 1993). Median age
at dispersal for females is 2.5 years (75% of dispersers between 1.5-3.75 years of
age: C. Packer in litt. 1993)
Age at First Reproduction:
(W) While the onset of spermatogenesis begins at 30 months in males (Smuts et
al. 1978), and females may begin mating at 24 months, successful first reproduction
generally happens only when pride membership is established. In the Serengeti, females
which remained within their natal pride first gave birth at five years (n=22). Females
which dispersed from their natal pride first successfully raised litters at an average
age of 8 years (n=8 emigrant cohorts); earlier litters generally did not survive. Males
generally establish pride tenure at 4-4.5 years, with larger coalitions (4+) establishing
residence earlier (Pusey and Packer 1987)
Cub Mortality:
(W) Mortality of cubs is rather high in lions, and is linked chiefly to periods of
prey scarcity, when kills may be more infrequent and cubs may not be able to eat well
from group-shared carcasses (Schaller 1972, van Orsdol et al. 1985). Infanticide
is also an important factor (Packer and Pusey 1983). Van Orsdol et al.
(1985) reviewed cub mortality (< 12 months) across a range of habitats: rates
ranged from 14-73%
Sex Ratio:
(W) Prenatal - 1 male:0.9 female (n=39); adult (5+ years): 1 male:2.1 females
(n=373 lions, Kruger NP: Smuts 1978b). Adult sex ratios are typically heavily
weighted in favor of females. The skew does not appear to be related to food supply or
density, but rather to differential rates of maturation, mortality and emigration
between the sexes (van Orsdol et al. 1985)
Age at Last Reproduction:
(W) female reproductive performance starts to decline at 11 years and virtually
ceases at 15 (Packer et al. 1988); 16 year-old males can still produce viable
sperm (Smuts et al. 1978), but reproduction probably completely ceases after
pride tenure is lost (8-10 years: Packer et al. 1988)
Longevity:
(W) males generally 12 (Hanby and Bygott 1991), and up to 16 years
(Smuts et al. 1978), females generally 15-16 (Hanby and Bygott 1991),
and up to 18 years (Bertram 1975a); C - average 13 years, but up to 25-30
(Guggisberg 1975)
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