Plate VIII. Fig. 1.—Content of Den Excavated in New Mexico.
Storage content of [Den No. 24, of Table 1], from Sandia Mountains, N. Mex. This is the largest lot of storage taken in the course of the investigations. The larger pile consists wholly of a valuable grass, Sporobolus cryptandrus strictus: the smaller of Russian thistle (Salsola pestifer.)
Plate VIII. Fig. 2.—Growth Following Elimination of Kangaroo Rats.
The same mound as shown in [Plate III, Figure 1], after three years of protection, the rodents having been killed out. Nearly as good grass recovery following poisoning operations occurred in the single excellent season of 1921.
At times, more especially in the seasons of active growth, some of the green and succulent portions of plants are eaten. This was very noticeable in the spring of 1919, when a most luxuriant growth of Mexican poppy (Eschscholtzia mexicana) occurred. Stomachs at this time were filled with the yellow and green mixture undoubtedly produced by the grinding up of the buds and flowers of this plant. Small caches of about a tablespoonful of these buds were also found in the burrows at this time. Occasionally in spring one may find a few green leaves of various plants, Gaertneria very commonly, tucked away in small pockets along the underground tunnels, indicating that such materials are used to some extent. As has been shown in detail, however ([Table 1]), the chief storage, and undoubtedly the chief food, consists of air-dry seeds.
The character of the storage, the absence of rain for months at a time in some years, and the consequent failure of green succulents show that without doubt spectabilis possesses remarkable power, as to its water requirements, of existing largely if not wholly upon the water derived from air-dry starchy foods, i.e., metabolic water serves it in lieu of drink (Nelson, 1918, 400), this being formed in considerable quantities by oxidation of carbohydrates and fats (Babcock, 1912, 159, 170). During the long dry periods characteristic of southern Arizona, no evidence that the animal seeks a supply of succulent food, as cactus, is found; and if it may go for two, three, or six months without water or succulent food, it is reasonable to suppose that it may do so indefinitely. In the laboratory spectabilis ordinarily does not drink, but rather shows a dislike for getting its nose wet. During the periods of drought the attacks upon the cactuses by other rodents of the same region, as Lepus, Sylvilagus, Neotoma, and Ammospermophilus, become increasingly evident. The list of plant species thus far found represented in the storage materials of spectabilis on the Range Reserve is shown in [Table 3].
Table 3.—List of all plant species found in 22 dens of Dipodomys spectabilis on the United States Range Reserve, near the Santa Rita Mountains, Ariz., with approximate total weights.
| Grasses. | |
| Grams. | |
| Aristida bromoides (six-weeks needlegrass) | 536 |
| Aristida divaricata (Humboldt needlegrass) | 9,412 |
| Aristida scabra (rough needlegrass) | 344 |
| Bouteloua aristidoides (six-weeks grama) | 3,093 |
| Bouteloua radicosa (grama) | 1,269 |
| Bouteloua eriopoda (black grama) | Tr. |
| Bouteloua rothrockii (seeds, 8,495; crowns, 3,517 grams) (crowfoot grama) | 12,012 |
| Festuca octoflora (fescue grass) | 70 |
| Panicum arizonicum (Arizona panic-grass) | 11 |
| Panicum hallii (Hall panic-grass) | Tr. |
| Pappaphorum wrightii | Tr. |
| Tridens pulchella | Tr. |
| Valota saccharata | Tr. |
| Other Plants. | |
| Alternanthera repens | Tr. |
| Anisolotus trispermus (bird's-foot trefoil) | 186 |
| Aplopappus gracilis | 1,030 |
| Apodanthera undulata (melon loco) | 55 |
| Astragalus nuttallianus (milk vetch) | 630 |
| Ayenia microphylla | Tr. |
| Boerhaavia wrightii | 885 |
| Chamaecrista leptadenia (partridge pea) | 5 |
| Echinocactus wislizeni (visnaga) | 5 |
| Eriogonum polycladon | 35 |
| Eschscholtzia mexicana (Mexican poppy) | 250 |
| Gaertneria tenuifolia (franseria) | Tr. |
| Collomia gracilis (false gilia) | Tr. |
| Heterotheca subaxillaris | Tr. |
| Kallstroemia laetevirens | Tr. |
| Lupinus sparsiflorus (lupine) | Tr. |
| Martynia altheaefolia (small devil's-horns) | 12 |
| Mollugo verticillata (carpetweed) | 324 |
| Oenothera primiverus (evening primrose) | 15 |
| Opuntia discata (prickly pear) | 15 |
| Loeflingia pusilla | Tr. |
| Lepidium lasiocarpum (peppergrass) | Tr. |
| Plantago ignota (plantain) | 818 |
| Polygala puberula (milkwort) | Tr. |
| Portulaca suffrutescens (purslane) | Tr. |
| Prosopis velutina (mesquite) | 1,570 |
| Sida diffusa (spreading sida) | 30 |
| Solanum elaeagnifolium (742 fruits) (trompillo, prickly solanum) | 156 |
| Puffballs and fleshy fungi (undetermined) | 12 |
Total species, exclusive of fungi, 41.
It will be seen from Table 3 that while a large number of species of plants are represented in the totals from so many dens, a majority of them are of very minor importance, and that the seeds of grasses are the principal storage and probably therefore the principal food material. Six of the most important species of grasses (disregarding species furnishing less than 5 grams) comprise 85.6 per cent of the total weight of storage from 22 dens. Crowfoot grama (Bouteloua rothrockii) stands first in quantity in the total, forming 39.4 per cent of all stored material, 46 per cent of the six important grasses, and 45 per cent of all grasses. The largest amount of storage of any one species of grass in any one den on the Range Reserve also is of this species, 2,205 grams[5] ([Table 1, den 1], [p. 20], and [Pl. VII, Fig. 2]). This is exceeded by a dropseed grass, Sporobolus cryptandrus strictus, which amounted to 5,455 grams in a lot from Albuquerque, N. Mex. ([Table 1, den 24], and [Pl. VIII, Fig. 1]).