UNIVERSITY OF CALIFORNIA 
 
 COLLEGE OF AGRICULTURE 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 BERKELEY, CALIFORNIA 
 
 CIRCULAR 296 
 
 Eevised May, 1925 
 
 September, 1925 
 
 CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 JOSEPH DIXON 
 (Contribution from the Museum of Vertebrate Zoology of the University of California) 
 
 Fig. 1. — Diagram showing methods of destroying ground squirrels to be employed 
 at different seasons of the year. 
 
 The ground squirrels are undoubtedly the most widely known and 
 at the same time among the most destructive mammals in California. 
 The large, long-tailed, grayish-brown species known as the California 
 or "digger" squirrel (Citellus beecheyi and subspecies) is the most 
 important in relation to man; first, because of its destructiveness to 
 
2 UNIVERSITY OP CALIFORNIA — EXPERIMENT STATION 
 
 crops; second, because it is a carrier of disease; and third, because 
 of the damage done by it to irrigation works. 
 
 Three races of the digger squirrel occur within the state : the dark- 
 colored northern form (the Douglas ground squirrel) which ranges 
 from San Francisco Bay northward throughout that portion of the 
 state which lies west and north of the Sacramento and Feather rivers ; 
 the brownish Beechey ground squirrel which occupies central Califor- 
 nia and the coast district south from the Golden Gate clear to the 
 Mexican line ; and the gray-toned Fisher ground squirrel whose habitat 
 lies in the southern San Joaquin and Owens valleys and south along the 
 western border of the Mohave Desert. The characters which serve to 
 distinguish these different races are not of any particular significance 
 in relation to the work of eradication, so that from this standpoint 
 the three forms may be considered as one. A knowledge of certain 
 habits of feeding, breeding and hibernation, however, possessed in 
 common by these animals is of the greatest importance in control work 
 and these habits are considered at some length in the following pages. 
 
 NATURE AND EXTENT OF DAMAGE 
 
 In 1920, Mr. F. E. Garlough, of the United States Biological 
 Survey, placed the average annual loss due to ground squirrels in 
 California at twelve million dollars. Allowing for the decline in 
 prices since 1920, it is the author's opinion that the annual loss due 
 to ground squirrels in this state is now not less than five million 
 dollars. 
 
 The California ground squirrel occurs in troublesome numbers in 
 most of the best farming and fruit-raising districts of the state. It 
 is a voracious feeder and reproduces rapidly. Many kinds of fruit 
 and practically all kinds of grain are subject to its depredations. This 
 squirrel prefers an elevated location for its homesite, and in digging 
 burrows it often honeycombs the banks of irrigation ditches, with 
 disastrous results. 
 
 The ground squirrel is a carrier and disseminator of bubonic 
 plague. Between May, 1907, and September, 1912, over one thousand 
 plague-infected ground squirrels were examined from a single county 
 in the San Francisco Bay region by the United States Public Health 
 Service. That the immediate danger of acquiring the plague through 
 ground squirrels has not passed, is shown by the virulent outbreaks 
 of the disease in Alameda County in 1918 and in Los Angeles County 
 in 1924. Their destruction in the infected districts would tend to 
 diminish the frequency of recurrence of this danger. 
 
ClRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 FEEDING HABITS 
 
 California ground squirrels have membranous cheek-pouches which 
 open inside the mouth and which are used to carry food, principally 
 grain, to the underground storerooms. These cheek-pouches are not 
 lined with fur as are those of the pocket gopher, but have thin walls 
 which readily absorb the strychnine on the outside of poisoned grain. 
 It has been demonstrated that ground squirrels are more readily 
 poisoned through these cheek-pouches by merely carrying poisoned 
 grain than through the stomach after they have eaten it. For this 
 reason the coated grain is preferred to that which has been soaked 
 in a strychnine solution. 
 
 The food and feeding habits of ground squirrels vary greatly with 
 the locality and season of the year. 1 During the rainy season, from 
 November to April, although they eat some grain, seeds or nuts that 
 have been stored during the previous summer, their main food is grass 
 and other green herbage. This results in serious loss in many locali- 
 ties, by reducing greatly the pasturage available for horses and cattle. 
 By weighing the food eaten by squirrels, I have found that 200 ground 
 squirrels on the open range consume as much green forage as one 
 steer, and 20 as much as one sheep. When green stuff is abundant, 
 comparatively little food is carried in the cheek-pouches. However, 
 by the last of March certain plants, such as alfilaria, have begun to 
 go to seed, and the squirrels then begin to use their cheek-pouches 
 extensively in harvesting these seeds. At this time the squirrels take 
 the poisoned grain readily, but later in the season when the cultivated 
 grain begins to ripen they are much harder to poison on account of 
 the abundant grain supply then available. 
 
 Ground squirrels are very fond of the soft pits of peaches, almonds 
 and apricots, and in getting these they destroy much fruit. On the 
 whole, however, the principal loss from ground squirrels is in the 
 grain fields, where the animals dig up and destroy the sprouting seed 
 and later pull down and destroy a vast amount of the ripening grain. 
 After the crops are harvested they congregate about the shocks and 
 stacks and continue to devour and carry off quantities of grain. At 
 this time watermelon rinds poisoned with strychnine are extremely 
 effective, since succulent green food is scarce. 
 
 i For a detailed account of general habits, see: Grinnell, J., and Dixon, J. 
 Natural history of the ground squirrels of California. Mo. Bull. State Comm. 
 Hort. (Sacramento), 7, nos. 11-12, 597-708, plates 5, 1918. 
 
UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 AESTIVATION OF THE GROUND SQUIRREL 
 
 There is evidence that a period of aestivation, or torpidity induced 
 by the dryness and accompanying food shortage in summer, obtains 
 among some of the adult ground squirrels in the valleys of California. 
 This period may extend continuously from late summer well through 
 midwinter, and thus involve hibernation as well as aestivation. Only 
 the old adults seem to "hole up," for the young adults (somewhat 
 over a year old) and the young of the year may be seen about the 
 burrows during suitable weather throughout the winter. A female 
 ground squirrel that lived under normal conditions in a dooryard was 
 kept under regular and continual observation. This squirrel did not 
 aestivate until its second year. Then and during each succeeding year 
 of its life it aestivated regularly, becoming very fat and retiring to its 
 burrow during the last week in August. When removed from the 
 burrow during this period, it was found to be in a torpid state and 
 respiration was not perceptible. It emerged in an emaciated condition, 
 with marked regularity, about the 22nd of each following February. 
 This habit of aestivation affords explanation of a case in my experience 
 in which all the squirrels that were active in a certain field in the fall 
 were poisoned or killed, and yet old breeding squirrels suddenly 
 appeared in this field the following February. This occurred when 
 there was seemingly no possible chance for re-infestation from the 
 surrounding fields. The extent of this habit of aestivation among our 
 ground squirrels is unknown. It is exceedingly difficult to follow any 
 individual squirrel through all its various activities for any great 
 length of time. However, it suggests the advisability of poisoning in 
 the spring rather than in the fall when some of the breeding stock 
 may be stowed away, out of the reach of poisoned grain. It is a ques- 
 tion, too, whether or not a dormant animal, in which respiration is 
 extremely slow, would be fatally injured by fumigation before the 
 gas disappeared. 
 
 TIME AND RATE OF BREEDING 
 
 The accompanying chart (fig. 2), based on over 10,000 female 
 squirrels examined by the United States Public Health Service during 
 the spring and summer of 1910, shows that the California ground 
 squirrel has a very definite breeding season which begins about the 
 first of February and lasts until the first of May. The maximum 
 number of pregnant females was found during the week ending 
 February 26. Most of the young are born about five weeks after this 
 
CIRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 5 
 
 date and may be seen running about at the entrances of the burrows 
 when a month or six weeks old. In low, warm valleys the breeding 
 season has been found to be somewhat earlier, while along the coast 
 and in the mountains the breeding season is about two weeks later 
 than the dates given. 
 
 The usual annual increase of a pair of ground squirrels consists of 
 one litter of from five to eleven. The average number of embryos 
 in pregnant females was found by the United States Public Health 
 Service to be 7.2. W. C. Jacobsen 2 found that on areas where control 
 
 
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 Feb. 
 
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 36 
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 Fig. 2. — Chart showing breeding season of California ground squirrels. (Com- 
 piled chiefly from data obtained from United States Public Health Reports, vol. 
 27, July 5, 1917, p. 1070.) Figures in left-hand column represent per cent of 
 
 females found pregnant; over 10,000 females examined. ■ represents 
 
 prevalence of pregnancy among female ground squirrels between January 15 
 and May 14. For example, during the week ending March 5, 27 per cent of 
 
 females examined were pregnant. shows approximately the time of birth 
 
 of the bulk of young squirrels. 
 
 operations had been carried on for two years or longer, and where 
 the food supply had increased by the diminution of the number of 
 squirrels, the litters were uniformly larger than where the work of 
 reducing the squirrel population had just begun. Thus in Tulare 
 County, where ground squirrels had been greatly reduced in numbers 
 for a period of years, Jacobsen found that 86 pregnant females con- 
 tained 846 embryos, an average of nearly 10 per litter. There is 
 
 2 Jacobson, W. C. Rate of reproduction in Citellus oeecheyi. Journal of 
 Mamm., 4, 58, 1923. 
 
6 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 some evidence that a second litter ia sometimes raised in a single 
 season, but this is certainly not usual. The important point is that 
 one breeding female killed before April 1, that is, before the young 
 are able to take care of themselves, is equal to the destruction of 
 from six to twelve squirrels later in the season. A wise man will go 
 after the squirrels early in the year, when "a stitch in time" will 
 literally "save nine." 
 
 METHODS OF CONTROL 
 
 The five most effective methods of destroying ground squirrels are : 
 (1) poisoning with strychnine; (2) fumigation with carbon bisulfide 
 or cyanide; (3) trapping; (4) shooting; (5) encouragement of the 
 natural enemies of the ground squirrel. 
 
 WHICH METHOD TO USE, WHEN, AND WHY 
 (See Fig. 1) 
 
 1. Strychnine-coated barley is best used during the dry season 
 because at this time the squirrels gather and store grain and hence 
 are easily poisoned through their cheek-pouches when in the act of 
 carrying the poisoned grain. Rain and heavy fogs tend to wash the 
 strychnine off the poisoned grain. It has been found by Mr. Garlough 
 that where ground squirrels are eating green alfilaria in quantity, 
 poison grain though eaten has little or no effect. This is explained 
 by the fact that this plant contains enough tannin, which is an 
 antidote for strychnine, to neutralize the poison. In certain localities 
 acorns are said to have a similar effect. 
 
 2. Powdered strychnine (sulfate) in fresh vegetables and fruit is 
 especially effective in the dry season when green food is scarce. 
 
 3. Carbon bisulfide or cyanide is most effective when the soil is 
 damp. When the ground is dry the gas escapes through the cracks 
 in the soil. 
 
 4. Trapping and shooting are effective at any time, but are from 
 six to twelve times more so before the young are out, before April 1, 
 than later in the season. 
 
 5. Reel-tailed hawks, golden eagles, badgers, weasels, and other 
 natural enemies of the ground squirrel will prove valuable allies in 
 the war on ground squirrels if they are merely allowed to live. It 
 costs little to let them alone, to go about their business in the natural 
 wav. 
 
ClRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 COMPARATIVE COST OF VARIOUS METHODS 
 
 In 1910, Dr. C. Hart Merriam 3 gave the cost of one treatment with 
 poisoned grain as 3 cents per acre and for one treatment with carbon 
 bisulfide ("waste-ball"" method) at 1% cents per burrow. 
 
 In 1912, Surgeon John D. Long 4 puts the cost of the various 
 methods of destruction, with carbon bisulfide at 90 cents per gallon, 
 as follows ; cost per acre, estimated on the basis of ten holes per acre. 
 
 Carbon bisulfide, with "destructor" (two treatments) $ .20 
 
 Poisoned grain (four or rive treatments) 35 
 
 Carbon bisulfide, waste-ball method (two treatments) 68 
 
 Surgeon Long reports that in actual practice one gallon of 
 bisulfide would treat from 200 to 250 holes when used with the 
 "destructor" and from 50 to 60 holes when used with the waste-ball 
 method. 
 
 Crude carbon bisulfide is quoted (April, 1925) at $1.15 per gallon, 
 in five-gallon lots in San Francisco. Strychnine is quoted from 78 
 cents to 93 cents per ounce for the sulfate, and from $1.00 to $1.19 
 per ounce for the alkaloid form, according to the quantity purchased. 
 The price of ammunition is also high, so that the present cost of the 
 various methods of destroying ground squirrels is, on the average, 
 considerably higher than Surgeon Long's estimate, which latter seems 
 to be the best and most accurate thus far published on the subject, 
 both as to the number of treatments required and as to the relative 
 cost. 
 
 (1) POISONING WITH STEYCHNINE 
 
 Barley as a vehicle for the poison is usually more attractive to the 
 ground squirrel than wheat. It is also less likely to be eaten by birds, 
 stock and poultry. It should therefore be used for this purpose 
 instead of wheat. Care should always be taken not to leave more 
 than a teaspoonful of poisoned grain in a place and it should never 
 be left where poultry can pick it up. The alkaloid form of strychnine 
 is only slightly soluble in water and is considered the best form to 
 use in preparing poisoned barley for the reason that it is not so 
 easily affected by fog and rain. When gathered and placed in the 
 cheek-pouches by the ground squirrel, the strychnine-coated barley 
 
 s Merriam, C. H. U. S. Dept. Agric, Biological Survey, Cir. 76:1910. 
 4 Long, J. D. United States Public Health Eeports, 27, no. 39, September 27, 
 1912. 
 
8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 often gets in its deadly work before the animal has a chance to detect 
 the bitter taste of the strychnine and reject the poisoned grain. 
 
 Formula for Strychnine-coated Barley. — The following is the 
 regular government formula 5 for preparing poisoned barley for 
 California ground squirrels. 
 
 Barley (clean grain) 16 quarts 
 
 Strychnine (powdered alkaloid) 1 ounce 
 
 Bicarbonate of soda (baking soda) 1 ounce 
 
 Thin starch paste % pint 
 
 Heavy corn sirup ^4 pint 
 
 Glycerin 1 tablespoonful 
 
 Saccharin y 10 ounce 
 
 Mix thoroughly 1 ounce of powdered strychnine (alkaloid) and 1 ounce of 
 common baking soda. Sift this into % pint of thin, hot starch paste and stir to 
 a smooth, creamy mass. (The starch paste is made by dissolving 1 heaping table- 
 spoonful of dry gloss starch in a little cold water, which is then added to % pint 
 of boiling water; boil and stir constantly until a clear, thin paste is formed.) 
 Add y± pint of heavy corn sirup and 1 tablespoonful of glycerin and stir thor- 
 oughly. Add y 10 ounce of saccharin and stir thoroughly. Pour this mixture over 
 16 quarts of clean barley and mix well so that each grain is coated. 
 
 Caution. — All containers of poison and all utensils used in the preparation of 
 poisons should be kept PLAINLY LABELED and OUT OF BEACH of children, 
 irresponsible persons, and livestock. 
 
 Placing Poisoned Grain.— The poisoned barley should be well 
 scattered over clean hard ground near the holes. Squirrel paths that 
 lead along fences or to or from the dens are good places in which to 
 scatter the grain. Poisoned grain will be largely wasted if dropped in 
 thick grass or in dusty places. It will also often be covered up if left 
 on the loose dirt at the entrance to the burrow. 
 
 Poisoning Fresh Fruits and Grain. — Strychnine sulfate is freely 
 soluble in fruit juices and these seem to conceal, to some degree at 
 least, the bitterness of the strychnine. Some of the best results in the 
 writer's experience in poisoning squirrels were secured with oranges 
 cut in halves which were then sprinkled with powdered strychnine and 
 left in the paths of the squirrels. Watermelon rinds, if cut into pieces 
 as large as one's hand and poisoned by sprinkling with powdered 
 strychnine, often prove very effective. It is wise to take every pre- 
 caution to place these baits in protected places, such as rockpiles, 
 where there is no chance for stock to reach them ; and it is also 
 advisable thoroughly to wash one's hands immediately after putting 
 out the poisoned bait. 
 
 5 Circular letter issued by Bureau of Biological Survey, U. S. Dept. Agric, 
 June, 1917. 
 
ClRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 (2) FUMIGATION WITH CARBON BISULFIDE OR CYANIDE 
 
 Carbon bisulfide gas is one of the best agents for destroying those 
 ground squirrels that have failed to take the poisoned grain or, having 
 once survived the poison, refuse to take it again. The following 
 facts should be kept in mind regarding the use of carbon bisulfide. 
 (a) The gas from carbon bisulfide is highly inflammable and it should 
 be kept away from all fires and exposed lights, (b) Being heavier 
 than air, this gas settles in the lowest places in the underground 
 burrow and hence will not go over an elevation higher than the 
 entrance of the burrow unless an "exterminator" or ' ' destructor ' ' 
 is used forcibly to pump the burrow full of gas or unless the gas is 
 exploded in the burrow, (c) When the ground is dry and full of 
 cracks the gas escapes and is, therefore, not nearly so effective as if 
 used when the ground is wet and the gas thus confined to the burrow. 
 (d) It should be used only in holes that are known to be occupied by 
 squirrels at the time of the treatment, (e) Carbon bisulphide should be 
 kept tightly corked as it loses strength rapidly on exposure to the air. 
 
 The two best methods of applying carbon bisulfide are by the use 
 of the "waste-ball" method and of the "destructor." The common 
 waste-ball method is to pour a tablespoonful of carbon bisulfide on a 
 piece of cotton waste, corncob, horse manure, or other absorptive 
 material, which should then be thrown as far down the hole as possible 
 and the opening immediately closed with earth. 
 
 Exploding the Gas. — The explosion of the gas in connection with 
 the waste-ball method is recommended where the ground is damp and 
 there is no danger from fire. A "destructor" should be used in grain 
 fields or in other places where there is danger from fire, since by its 
 use the burrow is pumped completely full of the carbon bisulfide gas 
 and the explosion of the gas is unnecessary. 
 
 A six-foot piece of %-inch pipe with one end closed and pointed 
 and the other end tightly wrapped with a rag soaked in coal oil adds 
 safety to the operation of exploding the gas in the burrow. After 
 the bisulfide has been confined in the burrow for a few seconds a hole 
 is made with the pointed end of the pipe through the dirt plug at the 
 entrance of the burrow. The gas is then "touched off" with the 
 torch, which has been previously lighted, on the other end of the rod. 
 It is advisable to stand well to one side of the burrow when doing this. 
 
 The second system of applying carbon bisulfide has been used by 
 Passed Assistant Surgeon John D. Long of the U. S. Public Health 
 Service, who devised a simple "destructor" which pumps the 
 
10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 vaporized bisulfide into the burrow. 6 Laboratory experiments showed 
 that the animal is but little alarmed by the gas and makes no effort 
 to escape or to seek fresh air. In ten or fifteen minutes after the gas 
 is pumped into the burrow the animal falls over and in from thirty 
 to forty-five minutes is dead. 
 
 This destructor (fig. 3) is composed principally of 18-gauge galvanized iron. 
 The circular top, bottom and piston are made from veneered wood so as to pre- 
 vent warping or splitting. The main parts of this apparatus are as follows: 
 An air chamber (1), containing the piston (10), is entirely surrounded by the 
 bisulfide tank (2). This tank is connected with the vaporizing chamber (4) 
 through the measuring cup (15). In operating the destructor, a short rubber 
 hose connected to the outlet (17) is inserted at least one foot into an occupied 
 squirrel burrow and tightly surrounded with dirt. Then the three-way cock (16) 
 is turned so that the measuring cup (15) is filled with y 2 ounce of refined 
 bisulfide, which is permitted by another turn of the cock to run into the 
 vaporizing chamber (4). 
 
 The pump has a double action, for air is admitted at the proper time at the 
 inlet valves (7) at both the top and the bottom of the cylinder when the piston 
 (10) is worked up and down by the handle (14). The air thus compressed escapes 
 through the outlet valves (8) into the air shaft (9), which in turn conveys it 
 to the vaporizing chamber (4). From the vaporizing chamber the bisulfide gas 
 is forced into the burrow through a rubber hose connecting with the outlet (17). 
 Fifteen double strokes of the pump forces 12 cubic feet of 1.5 per cent bisulfide 
 gas down the squirrel burrow; this is sufficient to kill the animal. The rubber 
 hose is then withdrawn from the burrow and the hole closed by stamping in 
 the dirt. 
 
 This destructor has been placed on the market through a San 
 Francisco firm. The Eureka Squirrel Exterminator and other similar 
 machines operate on principles similar to that of the destructor just 
 described, while a. rancher of mechanical turn of mind should be able 
 to construct a machine for the most part out of an old brass cylinder 
 and other materials from the scrap pile to be found about the average 
 ranch. The present high cost of farm labor favors the use of the 
 ''waste-ball" rather than the ''destructor." 
 
 Cyanide in the form of flakes, coarse powder, or dust which 
 liberates the poisonous hydrocyanic acid gas has recently been placed 
 on the market for use in gassing ground squirrels. From 1 to 2 ounces 
 per burrow is used. The material should be placed down in the hole 
 as far as possible, with a long-handled spoon. The burrow should then 
 be stuffed with grass or a newspaper and covered with earth. Care 
 must be exercised by the operator not to breathe the poison gas. This 
 material can be had in 65-pound cans at from 18 to 23 cents a pound. 
 
 e Long, J. D. United States Public Health Reports, 27, no. 39, September 27, 
 1912. 
 
ClRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 11 
 
 Fig. 3. — Sectional view of squirrel "Destructor." (Drawing from blueprint 
 furnished by United State Public Health Service.) 1, air cylinder; 2, bisulfide 
 tank; 3, filler; 4, vaporizing chamber; 5, veneer wood circles; 6, air space to lower 
 valves ; 7, inlet air valves ; 8, outlet air valves ; 9, air shaft ; 10, piston head ; 
 11, piston rod; 12, lock nuts; 13, cup leather packing; 14, handle; 15, measuring 
 cup; 16, three-way cock; 17, hose outlet; 18, air inlet to vaporizing chamber; 
 19, foot rest; 20, air vent in measuring cup; 21, air deflector; 22, bottom board. 
 
12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 
 
 Some ranchers report that they find it easier to use cyanide flakes 
 than carbon bisulfide and that the percentage of squirrels killed is 
 nearly or quite as good. In orchards cyanide is preferable to carbon 
 bisulfide. However, in a series of tests reported early in 1925 by 
 Mr. F. E. Garlough, of the United States Biological Survey, carbon 
 bisulfide was found still to be the cheapest and best fumigant for 
 general use in killing ground squirrels. 
 
 (3) TRAPPING; (4) SHOOTING 
 
 Where ground squirrels are digging into ditch banks, and in 
 similar cases where they must be disposed of promptly at any cost, 
 special means of getting rid of them must be adopted. Trapping 
 and shooting are two valuable methods of control for such local appli- 
 cation. While these two methods can be used at any season, the time 
 required to keep the traps properly set, which is essential to success, 
 and the high initial cost of the traps as well as the present high cost 
 of ammunition make them too expensive for general use on large 
 acreage. Trapping and shooting are useful in cleaning up the few 
 wise squirrels which escape the poison and carbon bisulfide, and in 
 reducing the breeding stock in the early spring before the annual 
 five-fold increase. 
 
 The No. 91 Oneida jump trap is the best, as it is lighter, easier to 
 set, and has a larger catching surface (pan or treadle) than the 
 ordinary steel trap with the outside spring. The jump trap lies flat 
 on the ground; the jaws have wide contact surfaces which reduce the 
 chance of breaking the animal's leg; and the construction of the 
 inside spring causes the trap to jump up and take a high grip on the 
 leg instead of on the foot only. Such traps may be set without bait 
 in the entrances to the burrows, or, baited with rolled barley, set in 
 the squirrel paths, or near the places where the squirrels are feeding. 
 In any case it is well to scrape out by a shove of the foot a slight 
 depression in which to place the trap, so that when set, the upper 
 surface will be flush with the surface of the surrounding ground. 
 The traps should be well secured. This is conveniently done by 
 passing a three-foot lath sharpened at one end through the ring in 
 the end of the chain, and then driving the lath well into the ground. 
 It will serve also as a marker, enabling one readily to find the trap. 
 
CIRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 
 
 13 
 
 (5) ENCOUKAGEMENT OF THE NATURAL ENEMIES OF THE 
 GROUND SQUIRREL 
 
 The killing-off of the natural enemies of the ground squirrel 
 removes Nature's most effective check on these destructive rodents. 
 Some of these age-long natural enemies of the squirrel are : coyotes, 
 badgers, weasels and wildcats, among mammals; rattlesnakes and 
 gopher snakes, among reptiles; red-tailed hawks and golden eagles, 
 among birds. Badgers, weasels and snakes capture the ground 
 squirrels in their burrows. Wildcats and coyotes lie in wait near the 
 burrows until the squirrels venture forth in search of food, when they 
 pounce upon them. Out of 186 stomachs of wildcats which have 
 recently been examined from forty different localities in California, 
 26 contained ground squirrels, 21 held wood rats, 13 contained gopher 
 remains, and 7 held mice. In this study rodents were found to con- 
 stitute more than half of the food of wildcats. Hawks and eagles 
 swoop down on the squirrels from their vantage points in the air. 
 The value of preserving as many as possible of these native enemies 
 of the ground squirrel is evident if this prolific animal is to be kept 
 within bounds. The aid of coyotes and rattlesnakes may be dearly 
 bought ; but badgers, gopher snakes, hawks and eagles cost us little or 
 nothing, and each one of these animals is catching ground squirrels 
 almost throughout its lifetime. The following observations by James 
 B. Dixon show what certain hawks and eagles actually accomplish in 
 destroying ground squirrels. The dead squirrels counted in the nests 
 cited represent merely the surplus which the old birds had carried to 
 the young. The squirrels that the old birds or the young may have 
 eaten on the day of observation are not taken into account. Hawks 
 and eagles it thus appears capture, when prey is abundant, far more 
 than they and their young can actually consume. 
 
 Destructive Rodents Found in Nests of Hawks and Golden Eagle 
 in San Diego County 
 
 Species of bird 
 
 Date 
 
 Young and eggs 
 
 Locality 
 
 Evidence 
 
 Red-bellied 
 Hawk 
 
 Apr. 3, 1916 
 
 3 young, 1 week 
 old, and 1 rot- 
 ten egg 
 
 Pala 
 
 1 ground squirrel 
 and 2 gophers 
 
 Western Red- 
 tailed Hawk 
 
 Mar. 28, 1906 
 
 1 day-old chick, 2 
 pipped eggs and 
 1 rotten egg 
 
 Vista 
 
 Remains of 2 
 ground squirrels 
 
 Golden Eagle 
 
 Mar. 26, 1909 
 
 1 day-old chick 
 
 Rincon 
 
 9 jack rabbits 
 
 Golden Eagle 
 
 Apr. 4, 1907 
 
 2 young, 1 week 
 old 
 
 Lilac 
 
 11 ground squirrels 
 in and about nest 
 
14 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION 
 
 OTHER METHODS OF CONTROL 
 
 Many small deciduous orchards are to be found more or less 
 isolated in foothill regions in different parts of the state. Squirrel 
 depredations in such orchards can often be prevented by tacking 
 smooth pieces of tin about the tree trunks. If the tinning is started 
 about two feet above the ground and continued upwards for two or 
 three feet it will usually keep the ground squirrels out of the trees 
 unless there are drooping branches which they can climb. 
 
 Seed corn has been protected from ground squirrels during 
 germination by being treated with coal tar. 7 Add one large spoonful 
 of coal tar to a gallon of boiling water. When the mixture has cooled 
 somewhat the corn may be stirred in and allowed to remain several 
 minutes without danger to germination. 
 
 SOME DIFFICULTIES IN GROUND SQUIRREL CONTROL 
 
 One of the most discouraging features in the work of ground 
 squirrel control is the indifferent, "do-nothing," attitude of a few 
 people in each locality who make just as little effort as the law allows 
 to rid their land of these pests. Many conscientious and progressive 
 ranchers have justly asked why they should continue to rid their 
 fields of ground squirrels when previous experience has shown that, 
 when cleaned up, these fields have been promptly restocked from the 
 squirrel-infested lands of their negligent neighbors. Now that we 
 have an adequate squirrel-eradication law, there should be less cause 
 for complaint on this score. 
 
 There is no question but that the most effective campaign against 
 ground squirrels is one in which the whole community joins. Cooper- 
 ation in this work is the only way in which all the ground can be 
 covered, and cooperation is therefore essential to success. The cost of 
 the war on ground squirrels to a community can be materially reduced 
 by purchasing strychnine and carbon bisulfide in wholesale quantities 
 and mixing its own poisoned grain under the supervision of the 
 Rodent Control Division of the State Department of Agriculture. 
 This will insure a supply of uniform, effective, and reliable poisoned 
 grain for each user at the lowest current price. 
 
 7 Lantz, D. E. U. S. Dept. Agric. Yearbook, Separate no. 708, p. 7, 1916. 
 
CIRC. 296] CONTROL OF THE CALIFORNIA GROUND SQUIRREL 15 
 
 BOUNTY SYSTEM A FAILURE 
 
 Some variety of bounty system intended to secure the eradication 
 of injurious rodents such as the ground squirrel has been tried in 
 Tulare and in other counties in California, but in most cases it has 
 proved far from satisfactory. Such a system usually results in an 
 early depletion of the funds provided to pay the bounty. When this 
 occurs the animals are soon permitted to regain their former numbers. 
 Bounties have not resulted in extermination of the animals aimed 
 at in any of the several states where tried. A bounty high enough 
 to secure extermination would be prohibitive on account of the cost, 
 as no state or county could stand the financial strain for any great 
 length of time. A lower bounty means that the animals will be 
 trapped only so long as it is profitable, after which they will be left 
 to breed up again. L. B. Nagler, Assistant Secretary of State in 
 Wisconsin says: 8 "I have had ten years' experience in auditing 
 bounty claims, and the results convince me that the system in vogue 
 is not only ineffective but wastef ul and, in a large measure, harmful. ' ' 
 
 It is the opinion of those best informed on the subject, that the 
 bounty system is not only vastly expensive and productive of endless 
 fraud, but that it fails to accomplish the end desired. 
 
 s Fins, Feathers and Fur, June, 1917, p. 1. 
 
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