The Natural History of Tassel-Eared Squirrels

10. The Kaibab Squirrel

116 The Kaibab Squirrel A January morning, just after sun-up, can be numbing in the pine forests of northern Arizona, at 8,000 feet above sea level. On such a morning it seems almost impossible to conceive of any creature surviving the twelve black, bitterly cold hours just past. . . . Emerging from the lofty needle-and-twig nest in which he spent the night, a large tree squirrel now moves quickly towards the outermost twigs of an upper branch . . . in the top of a favorite tree for breakfast. —J. G. Hall, “White Tails and Yellow Pines,” 1967 This chapter is dedicated to Dr. Joe Hall for his extensive research on the Kaibab squirrel. Introduction T he Kaibab squirrel was named after the geographical area where it lives, the Kaibab Plateau. Kaibab, a Piute word, means “mountain lyingdown.”In1882ClarenceDutton,withtheU.S.GeologicalSurvey , wrote, “The Kaibab is the loftiest of the four plateaus through which the Grand Canyon extends . . . We, who through successive summers have wandered through its forests and parks, have come to regard it as the most enchanting region it has ever been our privilege to visit” (ref. 1). The Kaibab Plateau is 95 km long and 55 km wide with much of its elevation at 1,830 m. The Kaibab Plateau was described by Rasmussen as unique because it is “the largest and best-defined of the block plateaus” (ref. 2). Approximately one-third of the Kaibab Plateau is covered by ponderosa pine forest, the chief plant indicator for the Merriam’s Transition Life Zone in the southwestern United States. The ponderosa pine forest is 10 T h e K a i b a b S q u i r r e l 117 about 90% (81,000 ha) in the Kaibab National Forest with the remaining approximately 8,000 ha within Grand Canyon National Park (ref. 3). Fifty-three years after Woodhouse’s discovery and description of the Abert’s squirrel, John Stewart, a trapper, collected squirrels from the Kaibab Plateau; from Stewart’s collection C. Hart Merriam described and named this squirrel Sciurus kaibabensis. Merriam stated that the Kaibab specimens he examined “differ strikingly from the well known Abert squirrel . . . [and were] scarce and wild” (ref. 4). Kaibab squirrels have black bodies with a snowy white tail. Abert’s squirrels have white bellies, grayish ventral surfaces, and a gray tail on top with white fur underneath. Both subspecies have the rufous dorsal patch extending down their backs. A small population of Kaibab squirrels living in Grand Canyon National Park have white bellies typical of the Abert’s squirrel and, conversely, black-bellied Abert’s squirrels have been reported near Flagstaff (ref. 5, 6). Kaibab squirrels have most likely been confined on the plateau since the Pleistocene epoch (ref. 7). Hoffmeister wrote in Mammals of the Grand Canyon that perhaps a small number of Abert’s squirrels crossed the canyon and river, colonizing the North Rim, probably during the late Pleistocene (ref. 8). Another group of researchers wrote, “Collectively, the genetics, morphologic, and paleoclimatic data offer strong support for a late-Pleistocene origin for S. a. kaibabensis via northward dispersal from Arizona” (ref. 9). Based on analysis of mitochondrial DNA, it has been estimated that S. a. aberti and S. a. kaibabensis have been separated for 235,000 years (ref. 10). The Kaibab squirrels have been described as “prisoners of geography ” (ref. 11). A Natural Landmark Brief for the U.S. Department of the Interior, National Park Service, written in 1962, stated, “In a local way it is as significant as are the finches of the Galapagos Islands which gave Darwin key insights into the importance of isolation in evolution” (ref. 12). In 1921, an article written by E. Hough in the Saturday Evening Post, titled The President’s Forest, described a trip to the Kaibab Plateau. Hough was told he would see white-tailed squirrels. “I never expected to see a white-tailed squirrel any more than I expected to see a purple cow or pink deer. . . . Sure enough we passed a placard on a tree ‘Range of white-tailed squirrel’ . . . And sure enough again, the forest service made good on its sign in less than a quarter of a mile! Came a flash of white from under a fallen tree, and there crossed our road a smallish dark animal with a spectacular banner over its back” (ref. 13). 118 C H A P T...