Connecting the two outposts,—the creosote bush and the choya,— with the holes that were in daily use there were some much-used runways, as shown on the map; and each side of each runway was barricaded throughout its length with spiny joints of the choya. A few of the joints were old and dry, but the majority were fresh and in full vigor. We estimated that about three hundred cactus joints were in use guarding those runways; and no coyote or fox of my acquaintance, nor eke a dog of any sense, would rashly jump upon that spiny pavement to capture a rat.
[Illustration with caption: FORTRESS OF A PACK-RAT, AT TUCSON DEFENDED BY THE SPINY POINTS OF THE TREE CHOYA (Opuntia fulgida)]
Beyond the cactus outpost the main run led straight to the sheltering base of a thick mesquite bush and a palo verde that grew tightly together. This gave an additional ten feet of safe ground, or about twenty-five feet in all.
On our journey to the Pinacate Mountains, northwestern Mexico, we saw about twelve cactus-defended burrows of the pack rat, some of them carefully located in the midst of large stones that rendered digging by predatory animals almost impossible.
The beautiful little Desert Kangaroo Rat (Dipodomys deserti) has worked out quite a different system of home protection. It inhabits deserts of loose sand and creosote bushes, where it digs burrows innumerable, always located amid the roots of the bushes, and each one provided with three or four entrances,—or exits, as the occasion may require. Each burrow is a bewildering labyrinth of galleries and tunnels, and in attempting to lay bare an interior the loose sand caved in, and the little sprite that lived there either escaped at a distant point or was lost in the shuffle of sand.
The Gray Squirrel (Sciurus carolinensis).—This beautiful and sprightly animal quickly recognizes man's protection and friendship, and meets him half way. Go into the woods, sit still, make a noise like a nut, and if any grays are there very soon you will see them. The friendships between our Park visitors and the Park's wild squirrels are one of the interesting features of our daily life. We have an excellent picture of Mrs. Russell Sage sitting on a park bench with a wild gray squirrel in her lap. I have never seen red or fox squirrels that even approached the confidence of the gray squirrel in the truce with Man, the Destroyer, but no doubt generous treatment would produce in the former the gray squirrel's degree of confidence.
I never knew an observer of the home life of the gray squirrel who was not profoundly impressed by the habit of that animal in burying nuts in the autumn, and digging them up for food in the winter and spring. From my office window I have seen our silver- gray friends come hopping through eight or ten inches of snow, carefully select a spot, then quickly bore a hole down through the snow to Mother Earth, and emerge with a nut. Thousands of people have seen this remarkable performance and I think that the majority of them still ask the question: "How does the squirrel know precisely where to dig?" That question cannot be answered until we have learned how to read the squirrel mind.
Small city parks easily become overstocked with gray squirrels that are not adequately fed, and the result is,—complaints of "depredations." Of course hungry and half-starved squirrels will depredate,—on birds' nests, fruit and gardens. My answer to all inquirers for advice in such cases is—feed the squirrels, adequately, and constantly, on cracked corn and nuts, and send away the surplus squirrels.
At this time many persons know that the wild animals and birds now living upon the earth are here solely because they have had sufficient sense to devise ways and means by which to survive. The ignorant, the incompetent, the slothful and the unlucky ones have passed from earth and joined the grand army of fossils.
Take the case of the Rocky Mountain Pika, or little chief "hare," of British Columbia and elsewhere. It is not a hare at all, and it is so queer that it occupies a family all alone. I am now concerning myself with Ochotona princeps, of the Canadian Rockies. It is very small and weak, but by its wits it lives in a country reeking with hungry bears, wolverines and martens. The pika is so small and so weak that in the open he could not possibly dig down below the grizzly bear's ability to dig.