Part 17

A: Mean daily ml./gm. wt./day B: Water consumption total ml. per day C: Temperature D: Humidity E: Per cent dietary protein F: Investigator

================+===========+=============+=======+=======+====+===== | A | B | C | D | E | F ----------------+-----------+-------------+-------+-------+----+----- | (.262) | (5.70) | | | | P. m. rufinus | .124-.699 | 2.71-15.07 | 20-23 | low | 23 | | | | | | | P. m. rufinus | (.101) | (2.39) | 20-25 | 24-47 | | | | | | | | P. m. osgoodi | .16-.25 | 3.2-4.3 | 18-22 | 10-20 | 23 | | | | | | | | (.126) | (1.74) | | | | P. m. bairdii | .082-.177 | 1.12-2.72 | 21 | 25-68 | | | | | | | | P. m. bairdii | .124-.182 | (2.37-3.17) | 20-25 | 24-47 | | | | | | | | | (.372) | (10.80) | | | | P. t. truei | .224-.561 | 7.0-16.92 | 20-23 | low | 23 | | | | | | | P. t. truei | (.085) | (2.77) | 20-25 | 24-47 | | | | | | | | P. l. nov. | .057-.117 | 1.36-2.29 | 21 | 25-68 | | | | | | | | P. l. nov. | | (5.36) | 18 | 62.5 | | ----------------+-----------+-------------+-------+-------+----+-----

Douglas Lindeborg, 1952 Williams, 1959 Dice, 1922 Chew, 1951

Table 8 shows average water consumption for several species of Peromyscus as reported in the literature, and as determined in my study. It is difficult to compare my results with most of the data in the literature, because of a lack of information as to protein, fat, carbohydrate, and mineral contents of foods used in other studies. Lindeborg (1952) and Dice (1922) fed mice on a mixture of rolled oats, meat scraps, dry skimmed milk, wheat germ, etc. described by Dice (1934). Their data on water consumption in P. maniculatus indicate that this mixture probably is lower in protein content than Purina Laboratory Chow, that was used in my experiments and those of Williams' (tables 8 and 9).

The amount of dietary protein consumed under natural conditions is not known for most wild animals. One index of the minimum amount of protein necessary is the amount required for an animal to maintain its weight. At best, this can be only an approximation of the required amount, for other factors, such as stress, disease, change in tissues during oestrus or gonadal descent, and changes in constituents of the diet other than protein, would all be expected to affect the body weight (Chew, 1965:145-147).

The data in Table 7 show that both species vary their food intake with changes in diet. Table 10 shows weight changes that took place in individual mice when fed each of the three diets. A change in weight of one gram cannot be considered as important, for the weight of an individual mouse fluctuates depending upon when he last drank, ate, defecated or urinated.

The only significant changes in weight occurred when mice were fed low protein food (Table 10). Individuals of P. truei lost 15.72 per cent and individuals of P. maniculatus lost 10.03 per cent of their total body weights on this diet. This indicates that food having a protein content of more than 10 per cent but less than 23 per cent is required for maintenance of weight in these animals.

Although knowledge of the amount of water consumed, ad libitum, by adult mice is valuable information, maintenance of the population depends upon reproduction and dispersal of young individuals. My trapping data indicate that only two to three per cent of the adults live long enough to breed in consecutive breeding seasons. In spring, the breeding population is composed largely of mice that were juveniles or subadults during the latter parts of the breeding season. Therefore, the critical time for the population may well be the time when the season's young are being produced. Any unfavorable circumstances, such as a shortage of food or water, that would affect pregnant or lactating females would be of primary importance to the integrity of the population.

TABLE 9--A Comparison of Mean Daily Water Consumption of Mice on High Protein Diets. Numbers in Parentheses Are Average Values; All Others Are Ranges of Values.

Column headings:

A: Temperature B: Relative humidity C: Investigator

================+===========================+=========+=======+========= | Mean daily H{2}O | | | | consumption | | | Species +-------------+-------------+ A | B | C | cc./gm. wt. | Total cc. | | | ----------------+-------------+-------------+---------+-------+--------- P. m. osgoodi | (0.27-0.54) | (4.6-9.3) | 18-22 C | 10-20 |Williams, | | | | | 1959 ----------------+-------------+-------------+---------+-------+--------- | (0.496) | (10.74) | | | P. m. rufinus | 0.186-0.764 | 4.54-16.57 | 20-23 C | low |Douglas ----------------+-------------+-------------+---------+-------+--------- | (0.653) | (19.57) | | | P. t. truei_ | 0.429-1.031 | 13.28-30.28 | 20-23 C | low |Douglas ----------------+-------------+-------------+---------+-------+---------

One would assume that pregnant and lactating females require more water than non-pregnant females. One might also assume that juveniles require different amounts of water and food than adults. Juveniles have less dense pelage than adults, and probably are affected more by their immediate environment because of their relatively poor insulation. Juveniles might also be in an unfavorable situation insofar as water conservation is concerned, because they are actively growing, and in most cases, acquiring new pelage; it is well known that these are times of stress for the individual.

TABLE 10--Weights of Mice at Start and Finish of Experiments, Showing Changes in Weight and Mean Weights, and Means of Changes in Weight (mean delta).

======================================================================== Peromyscus truei truei ----+---------------------+----------------------+---------------------- | Lab Chow | Hog Chow | Corn +------+------+-------+-------+------+-------+-------+------+------- No. |Start | End |[Delta]| Start | End |[Delta]| Start | End |[Delta] ----+------+------+-------+-------+------+-------+-------+------+------- 1 | 31.0 | 31.3 | 0.3 | 31.3 | 32.3 | 1.0 | 32.3 | 29.0 | 3.3 5 | 31.1 | 30.5 | 0.6 | 30.5 | 32.8 | 2.3 | 32.8 | 28.7 | 4.1 6 | 27.6 | 27.1 | 0.5 | 27.1 | 29.5 | 2.4 | 29.5 | 27.3 | 2.2 7 | 28.0 | 26.3 | 1.7 | 26.3 | 27.5 | 1.2 | 27.5 | 22.2 | 5.3 13 | 25.8 | 30.6 | 4.8 | 30.6 | 27.0 | 3.6 | 27.0 | 22.2 | 4.8 14 | 26.9 | 30.7 | 3.8 | 30.7 | 31.4 | 0.7 | 31.4 | 27.3 | 4.1 15 | 25.4 | 29.4 | 4.0 | 29.4 | 29.8 | 0.4 | 29.8 | 24.0 | 5.8 16 | 33.0 | 32.9 | 0.1 | 32.9 | 30.5 | 2.4 | 30.5 | 26.0 | 4.5 19 | 37.6 | 38.1 | 0.5 | 38.1 | 31.8 | 6.3 | 31.8 | 22.0 | 9.8 20 | 23.5 | 25.8 | 2.3 | 25.8 | 26.2 | 0.4 | 26.2 | 22.9 | 3.1 ----+------+------+-------+-------+------+-------+-------+------+------- [=Y]| 28.9 | 30.2 | 1.8 | 30.2 | 29.8 | 2.0 | 29.8 | 25.2 | 4.7 ----+------+------+-------+-------+------+-------+-------+------+-------

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.

Table 11 shows the amounts of water and food consumed by two females of each species while they were either in the later stages of pregnancy, or were nursing. Although the data in Table 11 do not cover the full developmental time of the litters involved, it is obvious that both lactating females of P. truei and one female of P. maniculatus consumed more water than the average for their species (Table 7). Water and food consumption was measured for both females of P. truei while they were nursing. The female that gave birth to litter A was left in the cage with the male for several days after the litter was born, resulting in another litter being born about 27 days after the first. Therefore, the record of this female represents an extreme case of stress (probably a common occurrence in nature) in which a female is nursing one litter while she is pregnant with a second.

The record of the female of P. truei that gave birth to litter B is the most complete, including data from the fifth day after parturition until the young were weaned on the thirty-third day after parturition. The record of the female of P. maniculatus that gave birth to litter C covers the last 10 days of nursing before the young were weaned. After being separated from her litter, this female drank more than the average amounts of water, on both high and low protein diets. Although the food and water were lost several times for the female of P. maniculatus with litter D, the period of time covered by the 14 days when water and food consumption were measured includes times just prior to parturition and to weaning of the young.

TABLE 11--Water and Food Consumed by Nursing Females of P. truei and P. maniculatus. Consumption Is Calculated on the Basis of Amount (Milliliters or Grams) Consumed per Gram of Body Weight per Day, as well as Total Amounts Used per Day.

Column headings:

A: Water used B: No. days C: Average weight D: ml. H_{2}O/gm./day E: Total water/day F: No. in litter G: Food used H: gms. food/gm./day I: Total food/day

=====================+=======+====+=======+======+=======+=== Female | A | B | C | D | E | F ---------------------+-------+----+-------+------+-------+--- P. truei (A) | 447 | 17 | 33.00 | .796 | 26.29 | 3 P. truei (B) | 676 | 28 | 32.70 | .738 | 24.14 | 3 P. maniculatus (C) | 191 | 10 | 19.45 | .983 | 19.10 | 5 P. maniculatus (D) | 133 | 14 | 24.35 | .224 | 5.46 | 6 ---------------------+-------+----+-------+------+-------+--- Female | G | B | C | H | I | F ---------------------+-------+----+-------+------+-------+--- P. truei (A) | 214.7 | 26 | 33.00 | .250 | 8.26 | 3 P. truei (B) | 120.5 | 24 | 32.70 | .153 | 5.02 | 3 P. maniculatus (C) | 47.8 | 10 | 19.45 | .246 | 4.78 | 5 P. maniculatus (D) | 180.1 | 21 | 27.42 | .312 | 8.58 | 6 ---------------------+-------+----+-------+------+-------+---

It is interesting that the female of P. maniculatus with litter C used much more than the average amount of water for the species, and even more per gram of body weight than lactating females of P. truei. Conversely, water consumption of the female with litter D was within one standard deviation of the mean for all adults of P. maniculatus. I infer that at least some lactating females of P. maniculatus are better adapted to aridity than are some lactating females of P. truei.

Table 11 also shows food consumption of the four females discussed above. All females, with the exception of the female with litter D, consumed amounts of food that lie within one standard deviation of the means for their species. The female with litter D had the most young, consumed the most food but drank the least water of the four females. Later, when separated from her litter and placed on the low protein diet, this female drank only .046 milliliters of water per gram of body weight per day. This figure is less than one-third of the average amount (.174) for this species (Table 7).

The records of water and food consumption for litters A, C, and D are given in Table 12; the mice in litter B persisted in placing wood shavings in the opening of the spout on their water bottle, causing loss of the water. The data show that mice in all three litters had an average water and food consumption within one standard deviation of the mean for adults of their respective species (Tables 7 and 12). It is interesting that juveniles of both species require no more food and water per gram of body weight than adults. This indicates that if a young animal survives the rigors of postnatal life until it is weaned, it is then at no disadvantage as far as food and water consumption are concerned. This would be greatly advantageous to the species, as a population, for the young could disperse immediately upon weaning, and go into any areas that would be habitable for adults of the species.

TABLE 12--Food and Water Consumed by Young Mice in Litters, After Weaning. Consumption Is Calculated on the Basis of the Amount (Milliliters or Grams) Consumed per Gram of Litter Weight per Day; Total Amounts Are Shown and Can Be Divided by Litter Size for Average Individual Consumption. Litter Sizes Are as Follows: A=3; C=5; D=6.