Ka. Nagy et Mj. Gruchacz, SEASONAL WATER AND ENERGY-METABOLISM OF THE DESERT-DWELLING KANGAROO RAT (DIPODOMYS-MERRIAMI), Physiological zoology, 67(6), 1994, pp. 1461-1478
Free-living Merriam's kangaroo rats in the Mojave Desert did not drink
, even when abundant rainwater was available for short periods in wint
er and summer, but they still obtained much more water than expected f
rom a diet of dry seeds alone. Year-round measurements of water influx
rates and field metabolic rates (via doubly labeled water), diet comp
osition (stomach content analysis), and body mass changes were used to
evaluate water and energy balance during each month of the year. From
late spring (May) through midwinter (December), kangaroo rats ate pri
marily the seeds of creosote bush (Larrea tridentata) and were able to
maintain water and energy balance on this diet even during the summer
drought. Dry seeds collected at the surface apparently were cached in
burrows where hygroscopic uptake of water from humid air increased th
e succulence of seeds before ingestion. In late winter and early sprin
g, kangaroo rats obtained abundant water and energy from their diet of
green vegetation (90% of diet dry mass) and arthropods (10%). Only in
late April and early May did these animals lose body mass, but that w
as clue primarily to reproductive effort (lactation) by females. Thus
at no time of year were kangaroo rats distressed by their comparativel
y dry, hot, and barren desert habitat. Field metabolic rates were high
est in winter, which suggests that these animals did not use torpor or
hibernation. On an annual basis, an individual free-living kangaroo r
at (mean body mass, 33.9 g) consumed nearly 1 kg (dry, matter) of food
, and the population (density, 17.5 animals per bectare) consumed over
17 kg ba(-1). This is a small fraction of net primary productivity bu
t can be a large proportion of seed production.