_Peromyscus maniculatus rufinus_ ----+---------------------+----------------------+---------------------- | Lab Chow | Hog Chow | Corn +------+------+-------+-------+------+-------+-------+------+------- No. |Start | End |[Delta]| Start | End |[Delta]| Start | End |[Delta] ----+------+------+-------+-------+------+-------+-------+------+------- 2 | 23.0 | 20.7 | 2.3 | 20.7 | 21.1 | 0.4 | 21.1 | 18.6 | 2.5 3 | 22.7 | 23.1 | 0.4 | 23.1 | 23.8 | 0.7 | 23.8 | 20.7 | 3.1 4 | 22.0 | 21.1 | 0.9 | 21.1 | 21.8 | 0.7 | 21.8 | 21.3 | 0.5 8 | 26.3 | 28.1 | 1.8 | 28.1 | 15.8 | 2.3 | 25.8 | 23.8 | 2.0 9 | 21.5 | 24.0 | 2.5 | 24.0 | 25.1 | 1.1 | 25.1 | 21.8 | 3.3 10 | | | | | | | 22.5 | 20.0 | 2.5 11 | 21.0 | 22.1 | 1.1 | 22.1 | 20.8 | 1.3 | 20.8 | 19.0 | 1.8 12 | 22.3 | 23.2 | 0.9 | 23.2 | 21.3 | 1.9 | 21.3 | 20.4 | 0.9 17 | 18.9 | 20.0 | 1.1 | 20.0 | 19.2 | 0.8 | 19.2 | 19.4 | 0.2 18 | 17.0 | 17.5 | 0.5 | 17.5 | 19.5 | 2.0 | 19.5 | 17.3 | 2.2 21 | 18.9 | 18.1 | 0.8 | 18.1 | 20.2 | 2.1 | 20.2 | 17.3 | 2.9 ----+------+------+-------+-------+------+-------+-------+------+------- [=Y]| 21.4 | 21.8 | 1.2 | 21.8 | 21.8 | 1.3 | 21.9 | 19.9 | 2.2 ----+------+------+-------+-------+------+-------+-------+------+------- Lindeborg (1950:76) found that 15 days before parturition, pregnant and non-pregnant females of _P. m. bairdii_ drank about the same amounts of water, that females consumed more water after the young were born and until they were weaned, and that water consumption increased with an increase in weight in young, growing individuals. He found that in the later stages of pregnancy, females of _P. m. bairdii_ required 36 per cent more water than non-breeding females; at 14 days after parturition, nursing females required 111 per cent more water than non-breeding females, and at weaning time, 158 per cent more water. Dice (1922:35) reported a 217 per cent increase in drinking of _P. m. bairdii_ before parturition, and 171 per cent increase while nursing. Several females of both species were bred prior to the start of the experiments described herein. As a consequence, it was possible to determine water and food consumption for lactating females of each species, and later, for their litters. Pregnant and lactating females, and newly-weaned litters, were fed laboratory chow throughout this experiment. The litters were separated from their mothers as soon as the young were observed to be eating, or no later than 33 days after birth.