HARVARD UNIVERSITY. LIBRARY OF THE MUSEUM OF COMPARATIVE ZOOLOGY 3"), ry 0 +_,— 3448 Issued March 9, 1912. Pee OEPARTMENT OF AGRICULTURE. a ae FARMERS’ BULLETIN 484. SOME COMMON MAMMALS OF WESTERN MONTANA IN RELATION (TO) AGRI- Peake AND SPOTITED FEVER. BY F CLARENCE BIRDSEYE, Assistant, Bureau of Biological Survey. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1912. LETTER OF TRANSMITTAL. U.S. DerarrMentr or AGRICULTURE, Burrav or Brotocican Survey, Washington, D. C., January 4, 1912. Sir: I have the honor to transmit herewith and to recommend for publication as a farmers’ bulletin a report on Some Common Mam- mals of Western Montana in Relation to Agriculture and Spotted Fever, by Clarence Birdseye, assistant in the Biological Survey. The investigations on which this report is based were carried on in western Montana for several years, especially in the Bitterroot Val- ley, in cooperation with the Bureau of Entomology and the Montana State Agricultural Experiment Station. As Rocky Mountain spotted fever is transmitted to man by wood ticks and as the earlier stages of these insects are passed almost wholly on native wild mammals, some of which are exceedingly destructive to crops, the facts here pre- sented have an important bearing on human health as well as on agriculture. Respectfully, Henry W. Hensuaw, Chief, Biological Survey. Hon. James Wixson, Secretary of Agriculture. [A list giving the titles of all Farmers’ Bulletins available for distribution will be sent free upon application to a Member of Congress or the Secretary of Agriculture. ] A ; 2 484 CONTENTS. 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See see eo = See Aes 29 MOTEL EO TORCCLTII Cole Meme Mam see el SR en Soe ee ence Sea 29 Darian oh ron Oia lero oh sone eA Gee eee aoa eS Ae Bere. one eee oem 29 OIRO EN I2 eee ete ee Sey are SNe ee. EA SA 30 SIGUE VENTE RE 5 2 SS oe Sa ek fe Se eet Mea ee ee oy ee a0 eR CME Sn Leer hae ee ra ae Sd eet ee Sek A os Aes ee cece. 31 ABS GIGMSNOSUR ere: Bva ae tere oe Sam eee aoc Bae Ce Se ee 31 eating vin pene a eee ne Le mee Maleate ty EO os DS oc vets 31 PORCSEGL Cy SVRLIA CO go re ae ee ne ee ts So See hs Cre ae ase ot 32 DT rafoybhntoye: Ciel atA wis Gease oe ako oe peas BORE see aoe eee Seeeee 32 TMI LOVCRD Da aeis see eee oe es ee cea te nh eee Riniee are sarees + 32 I EGTE OUTS Ge le mem G Gia oi SORES Ea a 34 Hormulanvn. Green alidiacsee eae pee eee see sou bones osu eee 34 Mornralam vie Alialta hay cso cce = 2 emer etarioe a Seis Sas. Soars Stacie 36 484 3 4 CONTENTS. Page. Pocket gophers... ..-s0e sees ec esece ved eseaccawssaduassegsunsauawweweves-- 56 Distribution ‘snd habitas , csaca ac ace dew ears le ee eee See oo. 36 Injury tO CropB. is ses.nscs5.) totes coun ees alae nee eee ee ee eaters 37 AB tick hose. 25 io wis 6 clase arnie ota dc ee ose ee ei ne 3! Poisort ges o's 5 Pena aase a wie ere aes ten aE nso 39 Formula VIL. Poiwonedvereiapléne.s ace ama wee aes ere. G5 39 TAD PUN Gs wiarc'sic ala: oops ree le mate eee es nO ae ae eet 40 Rab bite <2 ao wn cieteic a a Saree wim to apace aye tee ane re a a 40 Distribution: and habits... . sae eee eet ss. 37 31. Stock of apple tree killed by pocket gophers..........-..-----.----. 38 32. Pocket gopher mound in wheat field 3s2eoeeee eee eee eee ans. 39 33. Apple tree injured by rabbits..............-.-.--++-------+-------- 4] 34. Weasel, an active enemy of harmful rodents......-......-.---.-----. 44 484 SOME COMMON MAMMALS OF WESTERN MONTANA IN RELATION TO AGRICULTURE AND SPOTTED FEVER. INTRODUCTION. There are few localities in the West where the commoner species of native mammals, especially rodents, are so important as in certain parts of western Montana; for there they must be considered in rela- tion not only to agriculture but also to the Rocky Mountain spotted fever. Especially serious is the damage done to crops and young orchards by ground squirrels, pocket gophers, and rabbits; while in areas intended to be reforested the destruction of the tree seed by chipmunks and white-footed mice renders the extermination of these rodents necessary. The Rocky Mountain spotted fever is a germ disease which is com- municated from wild animals to human beings by the bite of the spotted-fever tick (Dermacentor venustus). In a number of experi- ments carried on by Dr. H. T. Ricketts + and others, spotted fever has been repeatedly communicated to healthy guinea pigs by the bites of wood ticks which had previously fed on animals sick with the fever. Not only has the fever been thus carried from one guinea pig to another, but it has been communicated directly to these animals by ticks picked up in regions where cases of the fever are known to have been contracted by men. Moreover, the germ which causes spotted fever is transmitted from infected female ticks to their off- spring, and in a number of experiments the disease has actually been communicated simply by the injection into a healthy guinea pig of a few crushed eggs of an infected tick. Such experiments as these—and numbers have been made, all with similar results—are enough to prove that ticks can and do transmit spotted fever. Only a small percentage of ticks, however, even in the worst “ fever country,” are infected, and thus people may be bitten by ticks many times without bad results. Moreover, infected ticks may bite people and communi- cate the disease and then become detached without being noticed there thus being in such cases no assignable cause for the infection. One of the current local theories is that spotted fever is caused by drinking impure of very cold water—in other words, that the 3 1Wourth Biennial Report (for 1907 and 1908) of State Board of Health of Montana, pp. 106-111 and 161-183. 484 5 6 COMMON MAMMALS OF WESTERN MONTANA, fever is contracted through the digestive system. Of course the drinking of bad water may, and undoubtedly often does, cause sick- ness. But that neither water nor anything else when taken into the stomach can possibly cause spotted fever is proved by the fact that even infected blood has been fed to guinea pigs, which are very susceptible to this disease, without bad results. In short, spotted fever, like malaria, is believed to be contracted only by blood infec- tion, and not, like typhoid, through the digestive system. In the brief life history of the tick there are four distinet stages— egg, “seed” or larva, nymph, and adult. Although the adult ticks have been found on mountain goats, coyotes, badgers, woodchucks, snow-shoe rabbits, and on the only bear examined, by far the greater number, at least 95 per cent, feed on domestic stock. When full of blood the females drop from their hosts to the ground, become inac- tive, and after a time lay as many as 4,000 eggs. They then die. After several weeks these eggs hatch, the young ticks, called seeds, being about the size of mites. These seeds then crawl up blades of grass or other low vegetation and, if opportunity offers, become attached to some passing small animal. After feeding on this animal for from three to eight days they become full of blood, drop off, and seek shelter. Then, after remaining inactive for a few days, they molt and emerge as nymphs, which somewhat resemble wood ticks, but are very much smaller. These nymphs, like the seeds, attach to some small animal—never, so far as known, to men—feed for a few days, drop off, become inactive, molt, and after about two weeks emerge as the third and last stage, the familiar wood tick. Thus the life cycle is completed in from one to three years. Any tick failing to find a host in any one of the three stages dies of starva- tion. Since it is known that spotted fever is communicated from wild animals to human beings by the bite of infected wood ticks and that the two younger stages live almost entirely on small native rodents— from which they occasionally contract the infection—it is evident that these tick hosts should be destroyed, at least around ranches. The extensive damage done by the same animals to agricultural interests is another important reason for their destruction. The chief purpose of this publication is to point out the best methods of destroying these native mammals. The investigations on which it is mainly based have been carried on for several years in the Bitterroot Valley, Mont., by the Biological Survey in coop- eration with the Bureau of Entomology and the Montana Agricul- tural Experiment Station. During the seasons of 1910 and 1911 the author, representing the Biological Survey, worked in coopera- 1 For detailed information in regard to the life history of the tick see Bull. 105, Bureau of Entomology. 484 COMMON MAMMALS OF WESTERN MONTANA. % tion with Mr. W. V. King, of the Bureau of Entomology, to whom he is indebted for many of the data concerning the host relations of the ticks, as well as for many observations on the distribution and habits of the mammals treated herein. POISONING RODENTS. Poisoning is in many cases the most effective and least expensive means of destroying harmful rodents; but methods of poisoning to be successful must be carefully worked out with reference to par- ticular kinds of animals and localities. The formulas given in this bulletin should be closely followed, as the amounts of poison recom- mended have been carefully determined. SOME COMMON RODENT POISONS. Strychnine, arsenic, and phosphorus are the three most generally used rodent poisons. The following is a brief summary of the char- acteristics of each: Strychnine is a vegetable poison obtained from the bean of the nux vomica tree, the chief supply coming from the Malabar coast, India. The strychnine of commerce consists of colorless crystals or white powder, and there are two forms commonly used as rodent poisons— the alkaloid and the sulphate. The alkaloid is only slightly soluble in water, and in rodent poisons is usually powdered and applied to grain in a coating of starch or flour paste. The sulphate dissolves readily in either hot or cold water and is used in solution. Both are deadly and act very quickly, causing tetanus, convulsions, and a speedy and comparatively merciful death. The bitterness of strych- nine is the chief drawback to its use, because ground squirrels, chip- munks, and some other rodents refuse to eat bitter baits when their natural food is plentiful. The addition of saccharine to strychnine baits has formerly been recommended, but recent experiments have shown that it does not conceal the bitterness of the poison, and is therefore of little value. Although an expensive poison, strychnine is so powerful that it is on the whole more economical than arsenic or phosphorus, and its use is strongly recommended by the department. Yellow phosphorus is extensively used as a poison for ground squirrels, rats, prairie dogs, and other rodents. But although it is both cheap and effective, the great personal danger accompanying its use and the fact that it causes a painful, lingering death are such serious objections that the Department of Agriculture strongly advises against its use. White arsenic is an almost tasteless, insoluble, rather weak, and very cheap poison, used extensively in rat baits. Its action on rodents is variable and uncertain. It often causes vomiting, and small doses 484 8 COMMON MAMMALS OF WESTERN MONTANA, tend to cause immunity. Although it is almost tasteless, ground squirrels and chipmunks refuse to eat it except when their natural food is very scarce, and then strychnine also would be eaten and would be much more effective. During the spring and summer of 1911 the author tried arsenic thoroughly and was forced to the con- clusion that it is not a satisfactory poison for any of the rodents mentioned herein, except woodchucks and possibly wood rats. Potassium cyanide is an exceedingly deadly and dangerous poison, which has been much used to destroy ground squirrels and prairie dogs. Although cheap, it absorbs moisture and quickly decomposes when exposed to the air, and is therefore unsatisfactory. It is not recommended, Corrosive sublimate, barium carbonate, squill, and nux vomica each have such serious faults that they are not at present recommended. METHODS OF USING STRYCHNINE. Three methods of applying strychnine to baits are recommended in this bulletin. In one the food is soaked in a solution of sulphate of strychnine, in another it is coated with starch or flour paste con- taining powdered alkaloid of strychnine, and in the third it is mixed with starch containing the alkaloid and is then compressed into squares or “ biscuits.” Grain soaked in sulphate solution is very bitter and is not recom- mended except when the bait is to be soaked in tallow to render it waterproof. A sulphate solution is valuable in preparing baits for rabbits and meadow mice. Starch or flour paste containing powdered alkaloid is recommended, because baits coated with these materials can be prepared much more vasily than those soaked in sulphate solution, because animals carry- ing coated baits are often killed simply by the absorption of part of the poison directly into the blood through the mucous membranes of the mouth or cheek pouches, and because the centers of kernels of coated grain remain sweet and are more freely eaten than those made bitter all through by soaking in sulphate solution. It is sometimes necessary to take special precautions to avoid killing birds, and in such cases “ oatmeal biscuits” are recommended. NECESSITY OF SPRING POISONING. Ground squirrels, chipmunks, and mice usually refuse to take poi- soned baits when natural food is abundant, and preparations which are effective at one time of the year are often of no use at another. The best time to use poison is in early spring, and the work should be done then if possible. Columbian ground squirrels can not be suc- cessfully poisoned at any other season. Thus, although 27 dead 484 COMMON MAMMALS OF WESTERN MONTANA. 9 ground squirrels, chipmunks, and mice (fig. 1) were found from 13 pints (7 cents’ worth) of poisoned grain placed early in the season, no dead animals were found from 5 bushels of the same preparations put out after seeds and berries became abundant. COOPERATION IN RODENT POISONING. One of the most serious difficulties encountered in a campaign against rodents or other pests lies in the refusal of a certain propor- tion of the people in most communities to take part in such work. The lands of these individuals then serve as breeding grounds from which the surrounding areas are constantly restocked. For this reason at the outset of such a campaign every effort should be made to Fic. 1.—Twenty-seven ground squirrels, chipmunks, and mice killed by 7 cents worth of poisoned grain. secure the cooperation of the entire community. It will greatly aid in a campaign against rodents to have the poison bought in quantity and the poisoned preparations made in large amounts at a central point, whence the people taking part may secure it at cost. If each individual made his own poisoned material, it would be a compli- cated and unduly expensive process for small ranchers. The con- venience of being able to get the prepared poison in small quantities would greatly encourage small proprietors to take an active part in the work. This is proved by the fact that every year thousands of dollars are spent for inferior and disproportionately expensive pro- prietary poisons simply because they can be easily obtained. One Montana orchard company last year bought 189 pounds of a certain 24208°—Bull. 484—12 2 10 COMMON MAMMALS OF WESTERN MONTANA, proprietary squirrel poison at a net cost of 23 cents a pound. In this bulletin a much more effective preparation costing not more than 12 or 15 cents a pound is recommended. Another advantage of co- operation is in the purchase of material at wholesale prices. Thus, while drug stores retail strychnine at from $1.50 to $2 an ounce, it may be bought in quantities of 5 ounces or more at from 60 to 65 cents an ounce. It is recommended therefore that, whenever possible, standard poi- sons be mixed in quantity by State experiment stations, counties, com- mercial clubs, granges, or other associations and then distributed at cost price to the large number of individuals who would thus be in- Fic. 2.—Columbian ground sguirrel. duced to use them. In the Bitterroot Valley a part of the spotted- fever fund appropriated by the State might well be used for this purpose. COLUMBIAN GROUND SQUIRRELS. DISTRIBUTION. The Columbian ground squirrel (fig. 2), known also as picket pin and gopher, is by far the most important rodent in western Montana in its relations both to agriculture and to spotted fever. It occurs also in northern Idaho, northeastern Oregon, eastern Washington, and the mountains of southwestern Alberta and southeastern British Columbia. AS TICK HOSTS. The Columbian ground squirrel is undoubtedly the most impor- tant host of the two younger stages of the fever tick, and is almost 484 COMMON MAMMALS OF WESTERN MONTANA. 11 always infested with ticks when occurring in suitable country. From the 341 specimens examined by Mr. W. V. King and myself in the course of these investigations 841 seed and 1,234 nymphal wood ticks were taken, an average of 6.09 for each animal. It can readily be seen, therefore, that in fever-infested localities the destruction of this most important host of young wood ticks must be an important supplementary part of any campaign for the control of the disease. HIBERNATION AND BREEDING. Although the habits of this ground squirrel vary considerably with elimaate and locality, in the warmer valleys it usually emerges from hibernation during the latter part of March. It begins rutting about a week or 10 days later sede’ as the gestation period is about 28 days, the young (averaging about 4 to 5 in a litter) are born in early May. At first they are blind, naked, and helpless. In about three weeks, however, they come to the surface of the ground for the first time and at once begin to eat various sorts of green food. Of 21 young squirrels weighed between June 6 and 12, 1911, about a week after their first appearance, the lightest tipped the scales at 2.75 ounces and the heaviest at 8 ounces. Eleven killed on June 10 averaged 3.75 ounces. The lightest of 30 adults weighed between May 30 and August 15 was 11 ounces and the heaviest 26 ounces, the average being 17.5 ounces. By about June 1 the old males have begun to recover from the strain of the rutting season and by the middle of July most of them are very fat. From then until they enter hibernation they remain close to their burrows and do little but sun themselves and eat. The old females do not begin to put on fat until about the middle of July and do not become so fat as the males until just before hibernating, if at all In most parts of western Montana the Columbian ground squirrels enter hibernation about the middle of August. In the colder parts, however, where they do not emerge from hibernation until the latter part of April, they remain active a full month longer; and at Almota, Wash., they “hole up” in July, having put in an appearance early in February. Thus it appears that the time they enter hibernation is usually about four and a half or five months after they emerge in the spring. FOOD HABITS. The Columbian squirrel, more than most other ground squirrels, prefers tender green vegetation to ripe seeds and grains. Probably as a result of these food habits its cheek pouches are small and little used. Among the green foods most attractive to these squirrels are dandelion heads, clover, alfalfa, timothy, lettuce, strawberries and’ various other berries, young carrots, bean and pea vines, and grow- 484 12 COMMON MAMMALS OF WESTERN MONTANA. ing grain. Oats (whole, hulled, or rolled) are preferred to any other grain; and wheat, though not so well liked, is readily eaten. Barley and rye are seldom taken. INJURY TO CROPS. Although ground squirrels are not so serious a pest in Montana as in some other States, the damage they do in many localities is sufficient to warrant their destruction. Growing grain is eaten by ground squirrels from the time it first appears above ground until the animals enter hibernation. (Mig. 3.) I have seen many wheat and oat fields which were seriously damaged by ground squirrels; and it is safe to say that every one of these animals in a grainfield annually causes at least a dollar’s loss. This great damage is well illustrated by the experience of a rancher near Pullman, Wash. In the spring of 1910 he bought 1,000 traps and iG. 3.—-Columbian ground squirrel burrow in wheat field. started to clear the squirrels off his whole ranch. Included in the land on which the animals were exterminated was an 80-acre piece from which the owner had for six years been unable to secure a crop, but after the squirrels were killed off this piece yielded an average of 35 bushels of wheat to the acre. Carrots, potatoes, beans, peas, and other garden truck are often seriously damaged. Figure 4 shows squirrel work in a carrot field near Florence, Mont. The manager of one of the orchard companies south- west of the same town reported that in 1910 ground squirrels caused the company a total loss of 5 acres of beans, the plants being attacked from the time they sprouted until the pods were formed. In hayfields squirrels cause serious loss both by eating hay and by covering considerable areas with their mounds, which are a great annoyance when the fields are mowed. In orchards the most serious damage is usually done to the irriga- tion systems; but Mr. Moody, president of the Como Orchard Land 484 COMMON MAMMALS OF WESTERN MONTANA. 13 Co., of Hamilton, Mont., reports that the depredations on that com- pany’s lands assumed a very unusual and serious nature, for the squirrels attacked the buds of the trees themselves and actually Fic. 4.—Carrots ruined by Columbian ground squirrels. killed about 45,000 trees in one year. This company at once took systematic steps to destroy the animals on their land, and spent over $1,700 for the work in 1910 and 1911. Fic. 5.—Washout caused by burrow of Columbian ground squirrel. Ground squirrel holes are a serious menace to the safety of irri- eation systems. Figure 5 shows a washout on a side hill, caused by irrigation water escaping through a squirrel burrow from an 484 14 COMMON MAMMALS OF WESTERN MONTANA, orchard on top of the bench. The chief engineer of the Bitterroot Valley Irrigation Co. writes that in 1911 $184.75 was spent to pro- tect the company’s main irrigation ditch and that each of the numer- ous development camps waged its own war against the squirrels. POISONING COLUMBIAN GROUND SQUIRRELS. The Columbian ground squirrels are probably the most difficult of the native rodents to poison. The chief reasons for this are that the animals prefer green vegetation to grain, that they do not store food, that they have an intense dislike for bitterness, and that they for some cause refuse to eat arsenic baits. For these reasons several years of experimenting have failed to produce a bait which is effective on the Columbian ground squirrels when green vegetation is abundant. But the work done during 1911 indicates that these ani- mals can be successfully poisoned if the poison is placed early in the spring when they first come out of hibernation. This means that the baits must usually be put out not later than the 1st of April and that they will not succeed after vegetation is well started. Hulled oats (or “ groats,”’ as they are technically known) are preferred by these squirrels to all other forms of grain and are much better than wheat for use in poisoning. Groats can be secured at oatmeal mills, usually at a cost of about 3 or 4 cents a pound. Ordinarily in the process of manufacture the groats are raised to a high temperature in coffee roasters, but the unroasted grain is better for squirrel bait, and should be secured where possible. Although hulled oats are more expensive than wheat, they should nevertheless be used, for they will give better results. Individual ranchmen making up small quantities of poison are likely to have difficulty in securing groats—another argument in favor of the wholesale manu- facture and retailing of squirrel poison by associations. Care should always be taken to avoid poisoning useful birds, and in some cases a special “ bird-proof” preparation is necessary. The poison which best meets these requirements is a small square “ bis- cuit ” of poisoned material, which when dry is too hard for small birds to peck to pieces and too large for them to swallow whole. These baits require considerable time to prepare, and therefore cost more than poisoned grain; but they are effective and are the only baits which will not endanger birds. They are, moreover, more resistant to rain than loose grain. The following preparations are recommended, but must be used early in the spring: FORMULA I. POISONED GROATS. Hulled’ oats. ((“groats 7) === See eee 4 quarts. Strychnine alkaloid (powdered) —~~--_--_____ 2 os re 4 ounce Wlour.._s2 2 eee 5 level tablespoonfuls. Cold water. 2 eee = eer ee 484 —Se- COMMON MAMMALS OF WESTERN MONTANA. 15 Place the flour in a bowl and add one-third cup of cold water, stirring until no lumps remain. Then stir in the other two-thirds cup of cold water and heat to boiling point over a slow fire, stirring constantly. Remove the paste from the stove, mix in the powdered strychnine alkaloid, and pour the poisoned paste over the groats, mixing until every kernel is evenly coated. Spread and dry the poison, and it may be either used at once or kept indefinitely. A gal- vanized iron washtub is an excellent receptacle in which to mix poisons. A heavy round-bottomed china or earthen cup and a round- headed iron bolt about 5 inches long make a good substitute for mor- tar and pestle with which to powder strychnine crystals. The addition of a quarter ounce of powdered dry extract of licorice and 2 teaspoonfuls of strawberry or raspberry sirup (such as is used at soda fountains) will aid to disguise the bitterness of the strychnine and will improve the taste of the bait, but these two ingredients are not necessary. Poisoned wheat may be prepared in the same way, except that only two-thirds as much flour paste is needed, for the glossy outer coat- ing of the kernels does not absorb moisture as readily as do groats. FORMULA II. POISONED BISCUITS. Ostimenites (role ding iS) en ey ee ee Pee ee 4 quarts. SELVCHOMINeGsALKalord) (pPOWOered a= =9— 4+ ounce. GIOSSEStarGha=—- === ane) See ee 23 heaping tablespoonfuls. Ni GCS) OS Ss ae ese) ee eee ee 1 quart. Stir the starch, dissolved in one-half cup of cold water, into 1 pints of boiling water, thus making a smooth paste of medium thick- ness, and into this stir the powdered strychnine. Then mix it thor- oughly with the oatmeal, forming a stiff dough. Press this dough into sheets one-fourth inch thick and cut it into one-half inch squares. After these have been dried in the sun—not in an oven—they will become hard and will keep indefinitely. This formula should make about 3,000 or 3,500 biscuits, each of which will contain enough poison to kill a squirrel. A little crushed starch or flour will pre- vent the dough from sticking to hands and utensils. In preparing small quantities of biscuits a flat board may be used to press the dough into sheets and a knife to cut it into squares. But where the baits are to be manufactured in bulk a rotary confectioner’s or drug- gist’s cutter will facilitate the work. PUTTING OUT THE POISON. A teaspoonful of loose grain, or two of the poisoned biscuits, should be placed at the entrance of each occupied squirrel hole. It will thus be more available for the squirrels and less likely to attract the attention of birds than if scattered broadcast. Poisoned baits 484 16 COMMON MAMMALS OF WESTERN MONTANA, should never be placed in ground-squirrel holes, for when so placed they are trampled into the dirt and are not eaten. When stock is ranging in the poisoned territory the grains may be scattered a little, not too much. TRAPPING. Next to poison, traps are the most effective means of destroying the Columbian ground squirrel. In fact, only by their use can the animals be exterminated in a given locality, for there are always some individuals which refuse to take poisoned baits or which escape fumigation. But since trapping is more expensive than poisoning, the two methods should be combined, as many as possible of the ani- mals being killed with strychnine and the rest caught with traps. Systematic trapping has not, in most localities, been as much resorted to as it should have been. It can not be too strongly recommended as a supplement to poison. The value of systematic trapping is well proved by the results which have attended its use in the rolling wheat lands of Whitman County, Wash., where it has steadily advanced in favor and has now Jargely supplanted poisoning. One or two of the ranch owners are operating 2,000 or more traps, and a number are using from 500 to 1,000. Mr. Mert Davis, of Pullman, is more than anyone else responsible for the introduction of systematic squirrel trapping, and his experi- ence is valuable. Two years ago he began trapping on a newly pur- chased ranch of 400 acres, all of which was very badly infested with squirrels. During the season of 1909 he used 1,200 traps, continuing the work through 1910 and into the spring of 1911, when only a few scattered squirrels remained; and these were secured soon after- wards. This ranch is now entirely free from squirrels, and, although the surrounding fields have not been trapped, is protected from in- vasion by keeping traps in the holes around the boundaries. Mr. Davis believes that old rusty traps are at least as good as shiny new ones. The squirrels caught were chopped up and fed to the chickens. METHODS OF SETTING TRAPS. There are two methods of setting squirrel traps, the * hole set ” and the “ surface set.” The hole sets are the ones almost universally employed at present. In this method jump traps, or ordinary steel traps (No. 1 are better than No.0),areset in every hole. (Fig.6.) If these traps are tended every day, all the squirrels are sure to be caught. The principal ob- jection to this method is the very large number of traps required, for since there are often ten or fifteen times as many holes as there are squirrels a large number of traps often cover surprisingly little ground. Mr. Claude Haines, a Whitman County rancher, bought 484 COMMON MAMMALS OF WESTERN MONTANA. 17 and operated 1,000 traps in 1911. He used 4-foot trap stakes split from waste fence posts, but believes that half laths would be cheaper Fic. 6.—‘ Hole set,’’ made with ordinary outside-spring steel trap. and fully as good. (Fig. 7.) He and another man worked one and three-quarter days staking and setting the 1,000 traps the first time, but on another occasion Mr. Haines alone set 500 traps in a day and Tic. 7.—Four-foot cedar trap stakes at burrows of Columbian ground squirrels. himself tended the whole 1,000 traps. He used nothing but hole sets. One of the unfortunate features of this method of setting traps is that weasels or other squirrel enemies are sure to be caught. 24208°-—-Bull. 484—12 3 18 COMMON MAMMALS OF WESTERN MONTANA. Surface sets are made by sinking traps flush with the surface of the ground near squirrel burrows and sprinkling oats or other bait in a circle just outside of the jaws. (Figs. 8 and 9). The advantages of this method of setting are that fewer traps are required to cover a given number of burrows and that enemies of squirrels using the burrows are not endangered. The disadvantages are that the surface sets require more time to make, that they occasionally catch meadow larks, quail, or other valuable birds, and that they are not always effective when green vegetation is abundant. “Jump” traps with their large pans are better suited to surface sets than are the small-panned outside-spring traps, for the animals are likely to walk around the latter sort of traps instead of stepping into them. Sometimes clods_ of earth placed on oppo- site sides of the traps serve to guide the ” ’ ic. 8.—* Surface set,’’ made with “jump” steel trap. squirrels into them. The most effective trapping can be done by using a combina- tion of hole and sur- face sets made as cir- cumstances suggest, and with jump traps, perhaps one-third of which are No. 1 and the rest No.0. In this case the No. 1 traps te should be reserved for the surface sets and the smaller size used in the holes. As a rule waste land, where burrows are numerous, can be trapped to the best advantage with surface sets, while hole sets are more effective in 184 Fic. 9.—Two Columbian ground squirrels caught in a surface-set ” jump trap. COMMON MAMMALS OF WESTERN MONTANA. 19 cultivated areas, where each squirrel has but a few holes. Traps should be visited at least once a day, in order both to secure the best results and to avoid causing imprisoned animals unnecessary suffer- ing. Figure 10 illustrates one way of handling a considerable num- ber of traps. Ordinary No. 1 steel traps cost about $125 to $130 a thousand and “jump ” traps are slightly more expensive. FUMIGATION. Fumigation with carbon bisulphid is very effective when employed early in the season while the ground is still damp. Dry ground Fic. 10.-—A convenient method of carrying 200 traps and stakes. rapidly absorbs the fumes. Crude carbon bisulphid suitable for this purpose costs from 8 to 10 cents per pound in 50-pound carboys or drums. Since it is a volatile liquid and rapidly loses strength on exposure to the air, it should be kept in tightly corked bottles or cans. When bisulphid is used to fumigate squirrel burrows, about a tablespoonful should be poured on a piece of loosely rolled cotton or other absorptive material and pushed as far as possible down the burrow, the opening to which should then be immediately closed. Every hole should be treated, and in case of outlying burrows a little larger amount of the bisulphid should be used. As carbon bisulphid is inflammable and the fumes highly explosive, it should never be 484 20 ‘COMMON MAMMALS OF WESTERN MONTANA. opened near a fire or where a person is smoking. Figure 11 shows an excellent outfit for using bisulphid. CONCLUSIONS. The Columbian ground squirrel is the worst rodent pest in western Montana, and is of especial importance in regions infested with spotted fever, where it is the principal host of the younger stages of the “ fever tick,” or wood tick. It is also the most difficult rodent in the Northwest to control. The methods of eradication recommended are early spring poisoning, followed at once by the systematic use of traps or carbon bisulphid. Fic. 11.—Outfit for use in bisulphiding ground-squirrel burrows. CHIPMUNKS. DISTRIBUTION. Several kinds of chipmunks occur in western Montana, but they are so nearly alike in appearance and habits that for the purposes of this work no distinction is made between them. (Fig. 12.) Although chipmunks are not nearly so important as are Columbian ground squirrels, they have a very definite relation both to agriculture and to spotted fever. AS TICK HOSTS. Probably more young wood ticks feed on chipmunks than on any other kind of animal except Columbian ground squirrels. Of about 190 examined during 1910 and 1911, many were found to be tick infested and some carried 50 or more seeds or nymphs. Chipmunks occur commonly around unoceupied log cabins, in stone and rail fences, and in pastures where there is more or less brush and fallen 184 COMMON MAMMALS OF WESTERN MONTANA. a timber, and in this way come into close contact with man and with domestic animals. When young ticks dropped by chipmunks around Fic. 12.—Yellow-bellied chipmunk. ranches molt and emerge as adult “wood ticks” they have a good chance to become attached to persons or domestic stock. It is there- Fic. 13. Chipmunk damage in wheat field. fore especially important that in any campaign’ against spotted fever an effort be made to kill off the chipmunks around ranches. 484 99 COMMON MAMMALS OF WESTERN MONTANA, INJURY TO CROPS. Although chipmunks occasionally do much damage to peas, straw- , or other such crops, they are chiefly harmful in wheat fields, where they cut the heads from the grain, usually after the kernels are in the dough stage. Often the animals start to climb the stalk, bend it down, cut off the head, carry it to a near-by stump or fence, and there hull and eat it. (Fig. 13.) Very frequently, however, they do not content themselves with this rather slow method, but break down stalk after stalk, taking only a few kernels from each.