Consumption of Herbaceous Vegetation and Water During Reproduction and Development of Merriam's Kangaroo Rat, Dipodomys merriami

Field data collected from a population of kangaroo rats, Dipodomys merriami, revealed that consumption of green vegetation is correlated with lactation but not the earlier stages of reproductive activity. This suggested that herbaceous vegetation plays a minor role in initiating reproduction but plays a major role in providing support for lactation. To evaluate the requirements for water during preand postnatal development, food and water intakes of female Merriam's kangaroo rat were measured in the laboratory during the nonreproductive state, during gestation, and during lactation. Nonreproductive and gestating females both consumed an average of 4.8 g water per day. During gestation growth rates are low, and water losses are probably of the same magnitude as in nonreproductive adults. Thus, water requirements during gestation would be similar to those during the nonreproductive state. Water intake increased markedly during lactation, averaging 10.7 g per day. Food intake increased to support the energy demands of growth. Thus, water intake derived from the catabolism of food increased as well. However, the majority of the increase in water intake resulted from increased consumption of carrots, which contained abundant free water. During lactation, nursling growth was supported at an average rate of 2.1 g water per day per nursling; the minimum support required is probably somewhat less. Two females were able to successfully wean a single nursling apiece while consuming water at about the same rate as nonreproductive females and with no demands on the body stores of the nursing mothers. Except in some cases of small litter size, sources of free water (e.g., herbaceous vegetation) are necessary for successful weaning of kangaroo rat nurslings.