All species of mammals require some source of water in captivity, although water sources and requirements vary widely among species. For example, kangaroo rats (Dipodomys) and pocket gophers of various genera live without free water in the wild because they get water directly from their food and retain metabolic water (Boice 1972). These taxa can be maintained in captivity by periodically feeding of small amounts of lettuce, celery,orapple.Thefrequencyofthese supplemental feedingsis dependent upon the ambient humidity in their environment. Adultheteromyids (e.g.,Dipodomys) seldom even require these. In fact, if provided with ad libitum access to free water, xericadapted species can become dependent upon these sources (Boice 1972), which can result in changes in physiological functions that might in turn pose problems for some studies