Part 15

Soft, shining fur, delicate coloring, and graceful form distinguish the silky pocket mice from others of their kind. The family of which they are members consists of rodents peculiar to America and includes many other species of pocket mice and kangaroo rats. All are provided with little pouches on each side of the mouth for gathering and carrying food, have proportionately long tails, and hind legs and feet more or less developed for jumping. Only in the most remote way, however, are they related to the jumping mice of the jerboa family.

The silky pocket mice vary in size from the tiny yellow species pictured on the accompanying plate, which weighs much less than an ounce, to forms considerably larger than the common house mouse. The little yellow pocket mouse is one of the smallest mammals in the world, and in addition is one of the most beautiful of our small species. Its bright eyes and the delicacy of its form and color, combined with the readiness with which, in most instances, it appears to lose all fear when caught and gently handled, render it extremely attractive.

As with the majority of other pocket mice, the silky-haired species are limited to the more arid parts of North America, and range from the Great Plains west of the Mississippi Valley to the eastern base of the Cascades, to the Sierra Nevada, and farther southward to the Pacific coast, and from the Canadian border to the Valley of Mexico. Vertically, the range of these mice extends from sea level to an altitude of more than 7,000 feet.

As with the majority of our wild mammals, little accurate information is available concerning their life history. They are habitants mainly of desert regions, where they prefer the areas of sandy loam, which produce an abundance of scattered desert vegetation. They are nocturnal and by day are seen only when driven from their nests. Their rather shallow burrows are made in soft soil, the situation varying a little with the species. Some species burrow only under the shelter of bushes or other vegetation; others out in the bare ground.

Each burrow commonly has grouped in a small area several entrance holes, which lead through tunnels to the central passageway, the nest, and the storage chambers. Usually there is a little pile of loose dirt thrown out on one side of a hole, or a group of holes may be in a little mound of earth. The entrances are usually stopped from within by loose earth, and if a person quietly thrusts in a short stick so as to remove the earthy plug and let in the light he may see the dirt suddenly returned to its place in little jets, as the occupant promptly kicks the door closed again.

The young, varying from two to six in a litter, are born in these little dens in warm nests of dried grasses. They have been found at all times between April and September, thus making it apparent that several litters are produced each season.

The silky, as well as the other kinds of desert pocket mice, do not drink water, and, as has been shown by experiments, they may be kept for months in thoroughly dry sand and fed on dried seeds without any resulting discomfort. Through the long pressure of desert environment they have developed the power to produce sufficient water for their physiological processes by chemical changes in the starch in their food, which are effected in the digestive tract.

Representatives of this group of mice are almost everywhere in the arid parts of their range, and in many sandy localities are extremely numerous and active at night, as shown by the multitude of little tracks in the dust at sunrise each morning. Their presence in the desert is indicated also by the many little conical pits half an inch or an inch deep, where they have located small seeds and dug them up.

They lie close in their burrows during cold or stormy weather, depending on their stores for food, but are not known to hibernate, although in the northern part of their range they are confined to their burrows for long periods.

At one of my camps in the desert of Lower California I found the silky and other pocket mice excessively numerous and so short of food that they swarmed about us at night with amazing lack of fear. My experiences with them are given in the accompanying account of the spiny pocket mice.

The silky and other pocket mice have many enemies, among the worst of which are the handsome little desert fox and the coyote. Others which continually prey upon them are the badger, skunk, and bobcat, as well as many owls.

=THE SPINY POCKET MICE= (=Perognathus hispidus= and its relatives)

(_For illustration, see page 515_)

Pocket mice are divided into several natural groups of species, all having certain characters in common, as a pointed head, lengthened hind feet and legs, and external cheek pouches for carrying food. The spiny group contains numerous species, the smallest of which is about the size of a house mouse and the largest nearly twice that size.

They are more slenderly built than the silky species and have longer tails, with the hairs lengthened along the terminal half, thus giving a slightly brushy or tufted appearance. Their most striking character is the distinctly coarser hair with long scattered guard hairs, like small bristles, which conspicuously overlie the fur on the hinder parts of the body and from which the common name is derived.

The distribution of the spiny forms, although nearly the same as that of the silky ones, is a little more restricted. All belong to the arid or desert parts of the West and Southwest, from South Dakota and middle California southward to Michoacan, near the southern end of the Mexican tableland, and throughout Lower California.

Some species inhabit the scattered growth of plants in sandy areas, but they are more generally characteristic of harder and more rock-strewn soil, rocky mesas, and foothill slopes. There a few species make burrows in open ground, sometimes with a single hole, but most of them make their nests under rocks, in crevices, or in burrows sheltered by such desert bushes as Covillea, Bursera, Olneya, Cercidium, and mesquites.

In these shelters pocket mice make little mounds a few inches high and ten or fifteen inches across. The mounds have several entrances on different sides, one of which generally shows signs of recent use, although by day it is kept closed from within by loose earth. Each of the many-entranced dens is occupied by a single animal. Early in the morning, before the wind fills them with dust, tiny trails are to be seen leading from these doorways toward the nearest feeding grounds and all about their haunts.

The spiny and the silky pocket mice, sharing much the same arid region, have the same food plants and are preyed upon by the same enemies. The food of these mice consists mainly of small seeds, including the wild morning glory, wild sunflowers, wild parsnips, and a multitude of others characteristic of the various areas they occupy.

Pocket mice are strictly nocturnal or crepuscular in habits and appear by day only when disturbed. If the plugged entrance to a burrow is opened, however, it will probably be quickly stopped up again from within by the annoyed householder.

The young, in litters of from two to eight, are born at irregular times according to the latitude and general weather conditions. In the south at least several litters appear to be born each year, the young being noted almost every month.

When camping alone for a few days in the desert near San Ignacio, in the middle of the peninsula of Lower California, I had a unique opportunity to learn something of the peculiarities of the various pocket mice. Three species were abundantly represented, including both the silky and the spiny kinds. They quickly learned that good hunting could be found in and about the tents for the rice grains and other scattered food and promptly took advantage of it.

As soon as approaching darkness began to render objects indistinct, from their burrows among the surrounding bushes they swarmed into camp and were busy throughout the night minutely searching the ground under the shelter tent for every particle of food. In order to see these interesting visitors to better advantage I placed a candle on a small box in the middle of the tent.

Five or six individuals, representing three species, often came within the circle of light at the same time. At first all were shy and when I made any sudden movement would leap in every direction, like grasshoppers, and quickly vanish. The smallest of the species, a member of the silky group, was the shyest of all and remained timid and reserved.

The two larger species, representing both the spiny and the silky groups, were much more bold and quickly became confiding and delightfully friendly. Their attention was promptly attracted to rolled oats which I scattered on the ground in a spot well lighted by the candle.

Sitting quietly close by the bait where the visitors congregated I soon had evidence that among themselves these little beasts are extremely pugnacious. The first to reach the food would fiercely charge the next comer and always try to leap upon its back, at the same time delivering a vicious downward kick with its strong hind feet. Occasionally the newcomer would charge the one already at the food.

When five or six were trying to secure sole possession of the small food pile there was lively skirmishing about the premises, as they alternately attacked and pursued one another over the sand and among the boxes and other camp gear scattered about. Amazingly quick in movements, they would leap now forward, now sidewise, now straight up a foot or more in the air, with almost equal celerity; and the direction of their movements when attacked was often unexpected. When running about on the level sand they had a steady, swiftly gliding motion, which their tracks showed was the result of a series of little jumps.

Both the spiny and the silky pocket mice became so confiding the first night that when I put my hand on the ground palm up with a little rolled oats in it the nearest pocket mouse would run to it, stop for an instant to smell the finger-tips, and then mount and sit quietly on the palm and fill its cheek pouches.

At such times the mice showed no uneasiness, even when raised in my hand to within a few inches of my eyes in order that I might observe their movements more closely. The motions of their front feet when putting food into the pouches were so rapid that it was impossible to follow them. The nose was held just over the food pile, and the cheek pouches would slowly but visibly swell as they were filled until they stood out like little bladders on each side of the head.

As soon as they were full the mice became uneasy to get away and would run from one side of my hand to the other peering down the abysmal depth of three feet to the ground without daring to leap. As soon as my hand was lowered to the ground the mouse darted away to carry the food to its store in the bushes twenty to thirty yards away, quickly to return with empty pouches.

The mice soon became so tame that while they were on my hand or on the ground I could with one finger of the other hand stroke gently the tops of their heads and backs and even pick them up by their tails and suspend them head down. When thus held they remained motionless, their tiny front feet like little closed hands held against their breasts. When lowered and released they would immediately resume the filling of their pouches as though nothing had happened. Several individuals of the dozen or more which made free of the tent had lost part of their tails, so that they could be readily distinguished.

One of these little bobtails was so gentle and confiding that I became much attached to it. It would permit all manner of familiar treatment, such as being picked up by one foot or by the tail, or being turned on its back. With this confidence came a sense of proprietorship in the good things here so suddenly and mysteriously plentiful, as was shown by his attitude toward his fellows.

Again and again when he was filling his pouches from a pile of rolled oats in my hand I lowered it in a gently sloping position within ten or fifteen inches of another mouse gathering food on the ground. Thereupon the little bobtail in my hand would invariably leave the task of filling his pouches and without hesitation leap down on the back of the one on the ground. The surprised animal thus assailed from an unexpected quarter always fled in terror.

After a short pursuit the bobtailed one would come running back and instead of going to the equally inviting pile of food on the ground would come straight to my hand and complete his task. The industry of the little animals appeared to be tireless, as working swiftly they made trip after trip with pouchloads of food to their stores and quickly returned. One night I watched this strenuous work for two hours until I retired.

The abundance and boldness of pocket mice and kangaroo rats at this place led me to believe that there had been a former abundance of their food here, resulting in a large increase in the rodent population, but that it was then becoming scarce through a failure of rain to renew the seed harvest. The invariable outcome in such cases is for the small rodents dependent on seeds and fruits to be reduced by famine until they become rare, where previously they existed in great numbers. This is one of Nature’s processes whereby the danger of the overwhelming increase of any species is automatically prevented.

=THE POCKET GOPHERS= (=Geomys bursarius= and its relatives)

(_For illustration, see page 515_)

With the exception of the moles no other extensive group of American land mammals is so highly specialized for a peculiarly restricted mode of life as the pocket gophers. They form a strongly marked family, the Geomyidæ, which includes various genera and many species, all very similar in external form, but varying from the size of a large mouse to a massively formed animal equalling a large house rat in weight.

Without exception they are powerfully built for their size, the head and front half of the body being extraordinarily muscled to meet the demands of their mode of life. The broad blunt head is joined almost directly on the body. The eyes are small and have the restricted vision to be expected from animals living underground. The ears are reduced to little fleshy rims about the openings, and the short naked tail is provided with nerves, which render it useful as an organ of touch.

The front teeth are broad, cutting chisels, and on each side of the mouth is a large pocket in the skin used for gathering and carrying food. On the front feet are long claws, which, when not being used to dig or handle earth, are doubled under, against the soles of the feet, so that the gopher walks on the back of them much as the ant-eater walks on its folded claws.

Peculiar to North America, pocket gophers occupy a great area extending from Illinois, Florida, and the Gulf of Mexico to the Pacific coast, and from the plains of the Saskatchewan, in Canada, southward to Panama. Their vertical range within these limits extends from sea level to timber-line, at above 13,000 feet on some of the high volcanoes of Mexico. The family attains its greatest development in that wonderful region of plains and volcanoes lying about the southern end of the Mexican table-land.

In the United States these animals are best known as “gophers,” but in the range they occupy in the Southeastern States they are called “salamanders” and in Mexico are widely known as “tuzas.” As a rule they frequent treeless areas, but are found also in many types of forests from among the palms and other trees of the tropical lowlands to the oaks, pines, and firs on the mountain sides.

All members of the family live wholly underground, in many-branched horizontal tunnels, which they are continually extending in winding and erratic courses about their haunts. The tunnels are from two to about five inches in diameter, according to the size of the animal, and while usually less than six inches below the surface, the approaches to the nest and storage chambers sometimes drop abruptly two or three feet below the regular working tunnels to the level of the living quarters. At intervals along the tunnels short side branches are used as sanitary conveniences, thus enabling the occupant to keep the main passageways in a habitable condition.

The courses of the underground workings are roughly indicated on the surface by series of piles of loose earth brought up through short side passages as the tunnels are extended. These little miners’ dumps of earth vary with the size of the animal, sometimes containing more than two bushels. The outlets of the passages leading to the surface are kept plugged with loose earth. When these animals are numerous the ground is thickly dotted in all directions with earth piles, and the caving caused by the network of tunnels just below the surface renders walking difficult. The perpetual industry of these rodent miners outclasses that of the proverbial beaver.

Gophers are both diurnal and nocturnal, the gloom of their tunnels scarcely varying except when one of the outlets is temporarily opened. They are averse to light, and if the plug to a freshly made opening is removed the observer may soon catch a glimpse of the owner as he suddenly thrusts his head into view for a moment before again plugging the door with earth.

Gophers dig their tunnels by using their teeth and the strong claws on the front feet. The loose earth is pushed along the tunnel by the head, the palms of the front feet, and the breast in little jerky movements until it is ejected on the surface dump.

Owing to their poor sight, heavy bodies, and short legs, gophers are clumsy and deliberate in their movements and peculiarly helpless in the open. Apparently appreciating this, they rarely venture from their underground shelter by day except when in grain fields or similar sheltering vegetation. Here they sometimes run out two or three feet to cut down a succulent stalk and drag it hastily within the entrance of the tunnel, where it is cut into short sections and placed in the cheek pouches if to be used as food or left on the dump if the object of the cutting is finally to secure the seeds or head of ripening grain.

During the mating season in spring pocket gophers run about clumsily from one burrow to another and may often be seen on the surface by the light of the rising sun. Most of their short trips above ground are made at night, when they sometimes swarm out and wander over a limited territory. Their night wanderings are proved in California by the many bodies which the morning light often reveals in the sticky crude oil on newly oiled roads which the gophers have tried to cross.

From one to seven young are born in a litter, but whether there is more than one litter in a season or not is unknown. The young when about half grown migrate to unoccupied ground sometimes one or two hundred yards from the home location and make tunnels of their own.

The food of pocket gophers consists mainly of tubers, bulbs, and other roots, including many of a more woody fiber. Whole rows of potatoes or other root crops are cleaned up by the extension of tunnels along them. Sometimes the animals follow a row of fruit trees, cutting the roots and killing tree after tree. In grain and alfalfa fields they are great pests, and in irrigated country their burrows in ditch banks often cause disastrous breaks.

The big tropical species sometimes exist in such numbers as to render successful agriculture very difficult. Sugar-cane planters in many parts of Mexico and Central America are compelled to wage unremitting war on them to avoid ruin. I know of an instance on a plantation in Vera Cruz in which thousands were killed during a single season without stopping the damage from these pests, which swarmed in from the adjacent area.

The large external cheek pouches of pocket gophers are used solely for gathering such food supplies as seeds, small bulbs, and sections of edible roots or plant stems and transporting them to storage chambers located along the sides of the tunnels. Food is placed in the pouches by deft sidewise movements of the front feet used like hands, and so quick are they that the motions of the feet can scarcely be detected. The pockets are emptied by placing the front feet on the back ends of the pouches and pushing forward, thus forcing out the contents. In their tunnels gophers run backward and forward with almost equal facility, the sensitive naked tail serving to guide their backward movements.

Pocket gophers are stupid solitary little beasts, with surly dispositions, and fight viciously when captured or brought to bay. This attitude toward the world is justified by the host of enemies ever ready to destroy them. Among their more active foes are snakes and weasels, which pursue them into their tunnels; and badgers, which dig them out of their runways.

They are also persistently hunted day and night by foxes and coyotes. Moreover, by day various kinds of hawks watch for them to appear at the entrances of their dens, and by night the owls, ever alert, capture many.

When one gopher intrudes into the tunnel of another the owner at once fiercely attacks it. In some places I have seen Mexicans take advantage of this characteristic pugnacity by fastening the end of a long string about the body of a captured gopher and then turning it into an occupied tunnel, through a recently made opening. The owner, scenting the intruder, would immediately attack him, the combatants locking their great incisors in a bulldog grip.

The movements of the string would give notice of the encounter, and by pulling it out steadily both animals could be drawn forth and the enraged owner of the burrow dispatched. In this manner I have known an Indian to catch more than a dozen gophers in a few hours.

Pocket gophers are active throughout the winter even in the coldest parts of their range, but in many places must rely largely on food accumulated in their storage chambers.

Melting snow in the mountains and in the North reveals the remains of many tunnels made through it along the surface of the ground. These snow tunnels are often filled for long distances with loose earth brought up from underground, and after the snow disappears in spring the curious branching earth forms left, winding snakelike through the meadows, are a great puzzle to those who do not know their origin.

In a state of nature pocket gophers are constantly bringing the subsoil to the surface and burying humus. Over an enormous area they exist in such countless thousands that their work, like that of angleworms, is often of the most beneficial character. On bare slopes, however, their work is highly injurious, as it greatly increases erosion of the fertile surface soil and thus has its direct influence in changing world contours.

When civilized man arrives in their haunts and upsets natural conditions with cultivated crops the new food supply stimulates an increase in the gopher population and their activities immediately become excessively destructive and necessitate unremitting warfare against them.

=THE KANGAROO RATS= (=Dipodomys spectabilis= and its relatives)

(_For illustration, see page 518_)