Sydney Anderson

“ The topotypes of this subspecies are the most distinct of all the series which I have studied from the eastern Rocky Mountains, in terms of the degree of morphological departure from the norm for the species. After zygomaticus the following populations are arranged according to their degree of deviation from this norm (codiensis deviates most) : topotypes of codiensis, fusus and a population from southern Sweetwater County, Wyoming, and lastly the nanus-caryi complex. ”

“ Species of southern distribution, that are dependent at the latitude of Colorado upon the habitat provided by areas of lower altitudes, and that are here in Colorado near their northern limit comprise a third category that is not represented in the list of mammals from the Grand Mesa although such characteristic species as Ammospermophilus leucurus, Perognathus apache, and Dipodomys ordii occur as near as Grand Junction.
Approximately 55 per cent of the species of the mammalian fauna are boreal; no species of Sonoran affinities finds haven on the Grand Mesa. ”

“ Canyon after canyon has cut into the sloping green plain. These canyons are roughly parallel and all open into the canyon of the Mancos River, which forms the southern boundary of the Mesa Verde. If the observer turns to the north he sees the arid Montezuma Valley 2000 feet below. A few green streaks and patches in the brown and barren low country denote streams and irrigated areas. To the northeast beyond the low country the towering peaks of the San Miguel and La Plata mountains rise more than 4000 feet above the vantage point on the North Rim at 8000 feet. ”

“ The forearm is only 42 mm. long in one young male from Sonora. Three of 8 Sonoran specimens taken in July had open epiphyseal sutures but were of adult size. In summary of the reproductive data by states, Artibeus hirsutus is known to bear embryos in the following months: May in Sonora, July in Chihuahua, February in Jalisco, and May in Guerrero. These data, along with the presence of embryos and young of various ages among specimens taken at the same place and time, indicate that the species does not have a restricted breeding season. ”

“ In Wyoming the most distinct break in this cline is in the Big Horn Basin and if a detailed study of the species were made in Montana the break would probably be found where the mountains meet the plains, roughly as shown in Figure 1. There is a similar cline in western Montana in color. The mice are paler farther north as one approaches the Canadian border although they do not become so pale as insperatus. Darkness is a characteristic of several non-adjacent subspecies of Microtus pennsylvanicus, for example M. p. ”

“ The first specimen of the Mexican vole from Colorado was obtained on the Mesa Verde and has been reported by Rodeck and Anderson (1956:436) . Specimens have now been taken at seven localities on the Mesa. Prater Canyon is the only one of these localities at which any other species of vole was taken. There Microtus longicaudus and Microtus montanus were also obtained. Judging from the vegetation at the above localities, M. mexicanus is to be expected in drier areas with less cover than M. montanus inhabits, and in areas having less cover than those inhabited by M. longicaudus. ”

“ The interorbital breadth of meridionalis is on the average greater and the depth of cranium is less than in chiapensis. There is some overlap in the range of each of these two cranial measurements, but in [Pg 524] all meridionalis the interorbital breadth exceeds 42 per cent of the depth of cranium, and in all chiapensis is less than 42 per cent. The length of the incisive foramina in meridionalis, expressed as a percentage of the total length of the skull, is usually greater than in chiapensis.
One of our specimens (KU 71389) contained four embryos that measured 5 mm. ”

“ In these mice, as in other microtines (Elton, 1942; Piper, 1909) , there are seasonal, and irregularly multiannual fluctuations in population density, which sometimes are extreme. Consequently the mice at some times seem to be absent from suitable habitats, and at some other times occur there in amazingly large numbers.
Because the species is broken up into partly isolated, or at times completely isolated, colonies or local populations it may be supposed that various evolutionary forces such as selection and random genetic drift operate to foster variation. ”

“ Furthermore the geographic variation in one feature may be only partly correlated with the variation in another feature. The variation in M. p. pullatus is an example: Specimens from near Pocatello, Idaho, are darker than topotypes of modestus but specimens from Fremont County, Idaho, are indistinguishable from topotypes of modestus (Davis, 1939:315) . I have examined a number of mice from the Bitterroot Valley in western Montana and the color value for 12 adults is 2.7. They are slightly but not significantly paler than topotypes of modestus. ”

“ Data on volume warrant no conclusion other than one that can be drawn from the percentages of occurrence, namely that the major food sources used in August, 1956, by coyotes in these canyons were deer, berries, and porcupines and that other sources, though used, were relatively unimportant. Deer were common in the area. It is fortunate that coyotes remain to help regulate the deer population. Wolves, Canis lupus, which at one time occurred in the Park, are now gone. The coyote and mountain lion are the only sizeable predators that remain. ”

“ Individuals from our series in general resemble specimens of Reithrodontomys mexicanus orinus from the vicinity of Guatemala City but differ from the latter as follows: dorsal pelage brighter (with less suffusion of black) , "peppered" in appearance, shorter and sparser; ears distinctly paler, owing both to the paler color of the skin and the paleness of the hairs inside the pinna; dark tarsal stripe not extending onto hind foot; ears and hind feet uniformly smaller ”

“ The presence or absence of the third molar tooth was recorded for 88 specimens (28 from Sonora, Sinaloa, and Chihuahua, and 60 from Guerrero and Jalisco) . The third molar tooth is present on both sides of the lower jaw in all specimens except one (12413 Univ. Illinois) from Sonora which lacks both upper and lower third molars. The upper third molar is usually present on both sides. The exceptions are as follows: the above mentioned Sonoran specimen and one other Sonoran specimen, one specimen from La Bufa, Chihuahua, two from Jalisco, and five from Guerrero lack the tooth on both sides ”

“ The caudal index (38 and 35% in two series) is slightly larger than that cited by Hall (33.3%) and is not significantly different from that in nanus (35.2%) . The color in both young and old mice is variable, but in general is more yellowish, and less grayish, than in any other series studied.
There is a large area in western Colorado and eastern Utah, between the known ranges of M. m. fusus and M. m. amosus from which there are no specimens. Probably the species occurs only at certain places in this arid region which seems to be a partial barrier to the species. ”

“ Individual views have ranged from a desire to exterminate all the prairie dogs to a desire to leave them undisturbed by man.
In review: The early history of prairie dogs on the Mesa Verde is not well documented but reports are available of the absence of prairie dogs before settlement by white men, and of introductions of prairie dogs. Other reports indicate that prairie dogs have been observed far from established colonies; therefore natural invasion may account for the establishment of prairie dogs on the Mesa. ”

“ Distribution of the subspecies of Microtus pennsylvanicus in Wyoming and Colorado. Solid dots represent localities from which specimens have been examined, and triangles represent localities reported in the literature from which I have not examined specimens. ”

“ Weight in grams of the adults averaged 14.3 (12-17) .
Reithrodontomys gracilis gracilis Allen and Chapman.—Guatemala.—El Petén: Uaxactún, 1500 ft., 2 (KU 65384-85—April 3, 1955) .
These specimens are the first of the subspecies to be recorded from Guatemala. Uaxactún is near, but not within, the range of R. g. gracilis as mapped by Hooper (1952:131) . The male, KU 65384, and female, KU 65385, are adults with comparatively unworn molar teeth. Respective external measurements are: total length, 178, 175; length of tail, 106, 102; length of hind foot, 18.5, 19; length of ear from notch, 14, 14. ”