In arid ecosystems, the dry season is probably an especially challengi
ng time for animals to find adequate food and water resources. Both st
ressful and benevolent times of the year can be identified by measurin
g rates of water and energy use (with doubly labelled water), diet and
behaviour throughout a year in free-ranging animals. Such field studi
es have been completed on four species of arid-land mammals. Jackrabbi
ts (Lepus californicus) are strict herbivores, and most Mojave Desert
individuals have no access to drinking water, and depend on their food
for their water. When vegetation dries up during the summer drought,
most jackrabbits apparently die of dehydration and malnutrition, but p
opulations are replenished by bountiful reproduction after winter rain
s. However, springbok antelope (Antidorcas marsupialis), also strict h
erbivores, can maintain water and energy balance throughout the year i
n the Kalahari in southern Africa by drinking water if available, but,
if not, they obtain enough water from dietary plants, probably by fee
ding before dawn, when food items have taken up water from the humid a
ir. Antelope ground squirrels (Ammospermophilus leucurus) are omnivoro
us in the Mojave Desert, and are active diurnally. They have lower wat
er and energy requirements than non-desert mammals of the same body ma
ss, like many desert mammals, but their ability to find succulent plan
t or animal foods in all seasons appears to be their primary survival
tool. On the other hand, Merriam's kangaroo rats (Dipodomys merriami)
are essentially nocturnal, and were thought to be strict granivores th
at never drank. A recent study, done throughout a year in the Mojave D
esert, confirms their lack of drinking, but reveals that they eat much
green vegetation in late winter and spring, probably in connection wi
th reproduction. They obtain additional water throughout the year by c
aching dry seeds in humid burrows, where seeds take up water hygroscop
ically before being eaten. Although springbok, antelope ground squirre
ls and Merriam's kangaroo rats were in negative energy and water balan
ce at times during the year, only jackrabbits were severely stressed b
y the dry season. Each species has a unique suite of desert survival m
echanisms. Future research should include carnivores as well as arid-h
abitat marsupials.