The Natural History of Tassel-Eared Squirrels

2. Physical Characteristics of Tassel-Eared Squirrels

5 Physical Characteristics of Tassel-Eared Squirrels The most characteristic, as well as the most abundant species of Squirrel, is the Tuft-eared discovered by Dr. Woodhouse in the San Francisco Mountains. It is one of the largest, and certainly the very handsomest of all the North American species. Besides very beautiful and harmonious colors, it rejoices in the possession of longpointedear-tufts,extendinganinchormorefromtheedgeof the conch of the ear, which gives it a peculiarly sprightly and truly elegant appearance. —E. Coues, “The Quadrupeds of Arizona,” 1867 Tassels E ar tassels have been the identifying characteristic from the very first published account of these squirrels given by Dr. Samuel Woodhouse (ref. 1). Other researchers have either reported tassel measurements or noted their existence and colorations upon collecting the various subspecies (ref. 2, 3, 4, 5, 6). No significant difference is found in the tassel lengths of females and males during the year (ref. 7). Black coloration of the tassels is consistent across all reports. Tassels begin growing from the tips of the squirrel’s ears beginning in the early fall. By January the tassels are at their maximum length of about 4 cm, sometimes drooping at the tips (ref. 7, 8, 9, 10). Researchers speculate that tassels may offer some thermal protection for the ear tips from the winter temperatures since these squirrels do not hibernate but remain active throughout the winter. Thermoregulatory characteristics of squirrels such as increased lengths of guard hairs and darker 2 6 C H A P T E R T W O colored fur in the winter have been reported in some squirrels that do not hibernate (ref. 11). During the late spring, the black color bleaches to a dark brown or tan color, and as the squirrels gradually shed their tassels by July they are left with very short hairs along the edges of the pinna (ref. 8, 12). Adults of S. a. kaibabensis completely lack tassels in the summer (ref. 10, 13). While S. a. aberti and its related subspecies are the only tassel-eared tree squirrels in North America, there are tassel-eared red tree squirrels in Europe (S. vulgaris) and Japan (S. lis), and in Borneo, the tassel-eared ground squirrel (Rhithrosciurus macrotis) (ref. 11, 12, 14, 15). In 1941, Ed McKee cited a personal communication received from Vernon Bailey, author of Mammals of New Mexico, regarding a comparison of tassels of the Old World squirrels to tassels of squirrels of North America: “the ear tufts . . . are very different in the two groups and probably do not indicate relationships” (ref. 14). Physical Characteristics—Pelage and the Colors Colors of the Type Specimens of S. a. aberti and S. a. kaibabensis in Arizona Woodhouse described the dorsal color of the S. a. aberti specimen he collected in 1851 as “dark gray” and the ventral surface as white with the tail being gray on top and white underneath (ref. 1). S. a. aberti is the type specimen for the subspecies of tassel-eared squirrels. The term “agouti,” which means “banded pattern,” refers to the combination of white, black, and grayish blends of colors comprising the dorsal pelage of S. a. aberti. C. Hart Merriam gave the following description of S. a. kaibabensis in 1904: “Similar in size and general characters to S. aberti, but underparts mainly black instead of white, and tail mainly white all over instead of under side only” (ref. 5). Colors of S. a. ferreus in Colorado A study conducted in Rocky Mountain National Park described the three color phases of S. a. ferreus: typical S. a. aberti pattern, totally black, and dark brown. The latter two did not have any dorsal patches of reddish fur nor the black lateral line that separates the dorsal from the ventral fur on a typical S. a. aberti (ref. 16). When I visited the Denver Museum of Nature and Science and examined the collection of specimens of tassel-eared squirrels, the colors of S. a. ferreus brought to mind P h y s i c a l C h a r a c t e r i s t i c s 7 various shades of coffee—mocha, latte, cocoa—and spices such as cinnamon and nutmeg. The many published reports of tassel-eared squirrels use numerous descriptive terms and colors to portray the subjective descriptions of fur color (tables 2.1 and 2.2). In 1877, Elliott Coues and Joel A...