- A feral pig population on Santa Catalina Island, California, was
studied for 17 months beginning in July 1980. Density was estimated
to be 21 to 34 pigs/km² (95% confidence interval) using capture-recapture
techniques. Dry season home ranges determined from
radio-telemetry data were small and differed significantly between
boars and sows. Patterns of habitat use according to vegetative
community, topographic position, slope, aspect, elevation, vertical
distance to water, and horizontal distance to water were examined.
During the dry season, pigs preferred cool moist canyon bottoms, the
result of both a physiological need for free water and behavioral
responses to high environmental temperatures. Patterns of utilization
during the wet season appeared to be primarily a function of food
availability. Diets were primarily herbaceous, although small amounts
of insects and vertebrate matter were eaten, and varied seasonally.
Fruits and forbs were the most preferred foods in the dry season,
while fruits, grasses and forbs were most preferred during the wet
season. Seasonal differences in diets reflected changes in
availability and phenology of plants. Seasonal trends were apparent
in acid detergent fiber, cellulose, and crude protein levels in the diet, but not in acid detergent fiber, phosphorus, gross energy,
digestible energy, protein digestibility and cellulose digestibility.
Diets were characterized as high in fiber, low in energy and
seasonally deficient in protein. Kidney fat and femur marrow fat
indices indicated pigs declined in body condition in summer and fall,
and improved in winter and spring. Optimal performance of pigs on
Catalina appeared to be linked to the quantity of the acorn crop in
early fall and the timing and duration of fall-winter rains. A
seasonal pattern in breeding was evident, with conception apparently
linked to both nutrition and photoperiod. Fertility declined in late
spring and summer as photoperiod increased; onset of estrus and
breeding in fall or winter were regulated by nutritional status of
sows. Litter size as measured by fetal counts was 5.00 ± 0.36 S.E.,
and sows averaged 0.86 ± 0.17 S.E. litters over a 12 month period.
Most sows were older than 1 year when they first conceived, and litter
size increased from puberty and peaked at 2-3 years of age.
Intrauterine mortality of fetuses averaged 25% and piglet mortality
was estimated to be 58% prior to weaning. Mortality rates appeared to
be higher for piglets born in summer than in winter or spring.