SMALLER MAMMALS OF NORTH AMERICA 



565 



New Mexico, Arizona, Chihuahua, and Du- 

 rango. The Kaibab squirrel, which is even 

 more beautiful than its relative, shows marked 

 differences in appearance and yet is evidently 

 derived from the same species. 



The typical Abert squirrel lives in the pine 

 forests along the southern rim of the Grand 

 Canyon in northern Arizona, and the Kaibab 

 squirrel lives in the pines visible on the north- 

 ern rim of the canyon less than 15 miles away. 

 It is confined to an islandlike area of pine 

 forest above 70 miles long by 35 miles wide, on 

 the north side of the canyon, on the Kaibab 

 and Powell plateaus, directly across from the 

 end of the railroad at the Grand Canyon Hotel. 

 The two species live under practically identical 

 conditions as to vegetation and climate. 



In these sketches of our mammal life I have 

 repeatedly noted the effect of changing environ- 

 ment in modifying the animals subject to it. 

 In the present case the change in the squirrels 

 on the north side of the Grand Canyon has 

 evidently been brought about by that powerful 

 factor in evolution known as isolation. Cut off 

 from their fellows by the deepening canyon of 

 the Colorado, Kaibab squirrels have occupied 

 a forest island ever since, with the resulting 

 change in characters we now have in evidence. 



The home of both the Abert and the Kaibab 

 squirrels is almost entirely between 6,000 and 

 9,500 feet altitude, on the mountain slopes and 

 high plateaus overgrown with a splendid open 

 forest of yellow pine mixed in many places 

 with firs and aspens. Occasionally, as "food be- 

 comes scarce in their ordinary haunts, they 

 range up into the firs or down into the oaks 

 and pinon pines. In winter their haunts are 

 buried in snow, but in summer on every hand 

 present lovely vistas among the massive tree 

 trunks, varied here and there by gemlike parks. 

 Everywhere the ground is covered with grasses 

 and multitudes of flowering plants. In the 

 wilder parts of this fascinating wilderness 

 roam bears, mountain lions, wolves, deer, and 

 wild turkeys, and only a few decades ago still 

 wilder men, belonging to some of our most 

 dreaded Indian tribes. 



Although these squirrels commonly make use 

 of large knot-holes or other hollows in trees, 

 they regularly build high up in the branches 

 bulky nests of leaves, pine needles, and twigs 

 and line them with soft grass and shredded 

 bark. Sometimes several full-grown squirrels 

 may be found occupying one of these outside 

 nests, probably members of one family. They 

 are active throughout the year, but remain in 

 their nests during storms and severe winter 

 weather. In northern Arizona I have known 

 them to stay under cover for a week or two at 

 a time in midwinter. 



The young appear to be born at varying 

 times between April and September. Although 

 not definitely known, it seems probable that they 

 have two litters of from three to four young 

 each season. 



The seeds and the tender bark from the 

 terminal twigs of the yellow pine ( Finns pon- 

 der osa ) furnish their principal food supply. Dur- 



ing periods when pine seeds are not available 

 the squirrels cut the ends of pine twigs, letting 

 the terminal part bearing the leaves fall to the 

 ground, while the stem, several inches in length, 

 is stripped of bark. Often at times of food 

 scarcity the bark will be eaten for a consider- 

 able distance along the outer branches, almost 

 like the work of porcupines. The ground under 

 the pines where the squirrels are at work is 

 sometimes almost covered with the freshly 

 dropped tips of branches. 



The Abert squirrels also eat the seeds of 

 Douglas spruce, of the pinon pine, acorns, many 

 seeds, roots, green vegetation, mushrooms, 

 birds' eggs, and young birds. Now and then 

 they rob cornfields planted in clearings, but 

 they do little damage to crops. Some years 

 they are extremely numerous and are in evi- 

 dence everywhere; again they become scarce 

 and so wary that it is difiicult to see one, even 

 where its fresh workings are in evidence. 



Both these squirrels have a deep churring 

 or chucking call, sometimes becoming a barking 

 note resembling that of the fox squirrel. They 

 also have a variety of chattering and scolding 

 notes when excited or angry. At times they 

 become almost as aggressive as the red squirrel 

 and come down the tree trunk or to a lower 

 branch, whence they scold and berate the object 

 of their disapproval. 



When much alarmed they are expert at hid- 

 ing among tufts of leaves near the ends of 

 branches, on tops of large limbs, or behind 

 trunks. They will remain hidden in this way 

 for an hour or more, patiently waiting for the 

 danger to disappear, but one is often betrayed 

 by the wind blowing the feathery tip of its tail 

 into view. 



On the ground the tail is usually carried up- 

 raised in graceful curves. Here these squirrels 

 spend much time among fallen cones and in 

 digging for roots and other food. When they 

 walk they have an awkward waddling gait, but 

 when they are alarmed, or desire to move more 

 rapidly for any cause, they progress in a series 

 of extremely graceful bounds, which show the 

 plumelike tail to good advantage. When the 

 Kaibab squirrel is moving about on the ground 

 its great white tail is extraordinarily conspicu- 

 ous in the sunshine. This repeatedly drew my 

 attention to these squirrels, even at such long 

 distances that they would otherwise have been 

 overlooked. 



Although so heavily built, these squirrels are 

 adept in leaping from branch to branch and 

 from tree to tree. On one occasion a branch 

 on which an Abert squirrel was standing near 

 the top of a pine tree was struck by a rifle ball ; 

 the squirrel promptly ran to the end of a large 

 branch about fifty feet from the ground, and 

 although no tree was anywhere near on that 

 side, leaped straight out into the air, with its 

 legs outspread just as in a flying squirrel. It 

 came down in a horizontal position and struck 

 the ground flat on its under side and the re- 

 bound raised it several inches. Without an in- 

 stant's delay it was running at full speed across 

 a little open park and disappeared in the forest 



