Life History of the Kangaroo Rat | Page 5

feet altitude on the warm southwestern slopes of the Graham Mountains, near Fort Grant. Apparently spectabilis reaches its upper altitude limit in the Burro Mountains, N. Mex., where Bailey has found it sparingly on warm slopes up to 5,700 feet, and at the western base of the Sandia Mountains, east of Albuquerque, N. Mex., where dens occur at approximately 6,000 feet.
About Tucson it is undoubtedly more common in the somewhat higher portions of the Lower Sonoran Zone, above the Covillea association, than elsewhere (Pl. IV, Figs. 1 and 2). A few scattered dens are to be seen in the Covillea belt, but as one rises to altitudes of 3,500 to 4,000 feet, and the Covillea is replaced by the cat's-claws (Acacia sp. and Mimosa sp.) and scattered mesquite (Prosopis), with the Opuntia becoming less abundant, kangaroo rat mounds come more and more in evidence. Here is to be found the principal grass growth supporting the grazing industry, and the presence of a more luxuriant grass flora is probably an important factor in the greater abundance of kangaroo rats, both spectabilis and merriami. In this generally preferred environment the desert hackberry (Celtis pallida) is one of the most conspicuous shrubs; clumps of this species are commonly accompanied by kangaroo rat mounds.
In order to ascertain whether the banner-tailed kangaroo rat has any marked preference for building its mounds under Celtis or some other particular plant, all the observable mounds were counted in a strip about 20 rods wide and approximately 4 miles long, an area of approximately 160 acres, particular note being taken of the kind of shrub under which each mound was located. Of 300 mounds in this area, 96 were under Prosopis, 95 under Acacia, 65 under Celtis, 11 under Lycium, 31 in the open, 1 about a "cholla" cactus (_Opuntia spinosior), and 1 about a prickly pear (Opuntia_ sp.). There is apparently no strongly marked preference for any single species of plant. While both desert hackberry and the cat's-claws afford a better protection than mesquite--since cattle more often seek shade under the latter, and in so doing frequently trample the mounds severely--it appears that the general protection of a tree or shrub of some sort is sought by kangaroo rats, rather than the specific protection of the thickest or thorniest species.
The following records indicate particular habitat preferences of spectabilis as noted at different points in its range:
Occurs on open bare knolls exposed to winds, also on gravelly places at lower edge of foothills (Franklin Mountains, Tex., Gaut); here and there over the barest and hardest of the gravelly mesas (Bailey, Tex., 1905, 147); on open creosote-bush and giant-cactus desert (Tucson, Ariz., Vorhies and Taylor); on firm, gravelly, or even rocky soil on the grassy bajada land along the northwest base of the mountains, either in the open or under Celtis, Prosopis, Lycium, Acacia greggii, or other brush (Santa Rita Mountains, Ariz., Vorhies and Taylor); mounds usually thrown up around a bunch of cactus or mesquite brush (Magdalena, Sonora, Bailey); in heavy soil (Ajo, Ariz., A. B. Howell); loamy soil (Gunsight, Ariz., A. B. Howell); in mesa where not too stony (Magdalena, Sonora, Bailey); grassy plain (Gallego, Chihuahua, Nelson); in open valley and high open plains (Santa Rosa, N. Mex., Bailey); in grassy and weed-grown parks among the larger junipers, pinyons, and scattering yellow pines (Bear Spring Mountains, N. Mex., Hollister); on sand-dune strip (east side of Pecos River, 15 miles northeast of Roswell, N. Mex., Bailey); among Ephedra patches (San Juan Valley, N. Mex., Birdseye); in open sandy soil along dry wash (Rio Alamosa, N. Mex., Goldman); on sides and crests of bare, stony hills (Mesa Jumanes, N. Mex., Gaut); in open, arid part of the valley and stony mesas (Carlsbad and Pecos Valley, N. Mex., Bailey); about the edges of the plains of San Augustine and the foothills of the Datil and Gallina Mountains, and in the Transition Zone yellow-pine forest of the Gallina Mountains (Datil region, N. Mex., Hollister); on hard limy ridges (Monahans, Tex., Cary).
A. Brazier Howell notes that spectabilis occurs in harder soil than does deserti. This observation is confirmed by others, and seems to afford a conspicuous habitat difference between the two, for deserti is typically an animal of the shifting aeolian sands.
Usually, as on the Range Reserve, the rodents are widely distributed over a considerable area. Occasionally, as in the vicinity of Rio Alamosa, N. Mex., as reported by Goldman, they occur only in small colonies.
[Illustration: PLATE IV. FIG. 1.--RANGE CONDITIONS FAVORING KANGAROO RATS.
View on higher portion of Range Reserve, showing type of country where Dipodomys s. spectabilis is most abundant. Good growth of grama and needle grasses in October, following summer growth and before grazing off by cattle and rodents.]
[Illustration: PLATE IV. FIG. 2.--RANGE CONDITIONS LESS FAVORABLE TO KANGAROO RATS.
View on lower