Rex E. Marsh

Historical review of ground squirrel crop damage in California

The threat to crops from the California ground squirrel, Spermophilus beecheyi, is followed from the early Spanish mission fathers through the gold rush period and continues from the turn of the century to the present day. Included are the kinds of crops damaged and how the damage became more varied as agriculture became much more intense and diverse following World War II, i.e. post-1945. Damage to fruit and nut crops, as well as to field and vegetable crops, is discussed, along with the more unique speciality crops such as seed production and flowers grown for the commercial market. A brief review is given to some of the cultural practices which influence squirrel populations—both positively and negatively. The detrimental effect of the squirrel on range land management and reforestation receive due attention. Estimates of the multimillion dollar monetary losses caused by the ground squirrel to agricultural crops are assembled from previously published reports dating from 1910 to the present.

A BODY CAPACITOR-OLFACTOMETER FOR SQUIRRELS AND RATS

The body capacitor-olfactometer described herein was developed for the purpose of measuring quantitatively the number and duration of odor seeking (primarily food seeking) responses of wild ground squirrels (Spermophilus spp.) and rats (Rattus spp.) to various olfactory cues presented free of the in- fluence of taste, without the reward of food, and without requiring that these field-caught rodents first be trained to the olfactometer before their responses could be monitored. Species of rodents that weigh less than 250 grams possess a body capacitance too low to activate the sensor units, but there is no upper size limit. We believe that this olfactometer could be adapted for mouse-size rodents if ultrasonic, infrared, or some other type of sensor was employed in place of the body capacitor. Field experience has shown that many rodents are macrosmatic, having the ability to locate and remove single seeds of many kinds of crops regardless of whether man has buried them by hand or mechanically. Also, many rodents often naturally bury seeds for later relocation and consumption. Other ex- periments (Howard and Cole, 1967; Howard et al., 1968) have shown that deer mice (Peromyscus maniculatus), and presumably many other rodents, have no difficulty utilizing olfactory cues to locate buried seeds of conifers and cereals. In our ecobehavioral studies of wild rodents it usually is necessary to examine many field-caught animals for brief periods of time rather than sub- ject a small number of suitably conditioned individuals to repeated tests as is commonly done in psychobiology. The olfactometer described herein was developed to record the number and duration of a subjects response to from one to three odors being emitted simultaneously from nine stations in the olfactometer arena; it does not measure the olfactory thresholds of animals or the quantity of the test volatiles that are present. Instead, it monitors the frequency of searching responses and the duration of each visit an animal makes to an odor station in its search (digging) for the source of the intro- duced odors. Only one animal is placed in the olfactometer at a time. The change in response time animals make to the test odors following conditioning experiments, such as creation of bait shyness, also can be measured with the olfactometer. All experimental odors are presented in sufficient quantity to be readily detected by the test animal throughout the arena of the olfac- tometer. We have not attempted to determine the parameters of odor con- centrations that will work in this instrument; we merely make certain that sufficient but constant amounts of odor of each test substance is present so as to be readily detected by the subjects when they are in the arena.

Food habits of California voles, Microtus californicus, in artichokes, Cynara scolymus

Abstract The California vole (Microtus californicus) is the most serious vertebrate pest of artichokes (Cynara scolymus) in California. A microhistological analysis of the stomach contents of 45 voles collected at intervals from November 1983 to July 1985 from seven different artichoke fields indicated that artichoke was a significant and the major component of their diet during all seasons. In the spring (April) collections, the amount of artichoke consumed was somewhat reduced and about equal to all other food items combined due to increased consumption of grasses (wild oat, Avena fatua, and common foxtail, Hordeum leporinum) and/or oxalis (Oxalis pes-caprae) at that time of year. Other items consumed in relatively minor amounts by voles in artichoke fields were cheeseweed (Malva parviflora), chickweed (Stellaria media), mustard (Brassica spp.), and insects. This study clearly illustrates that artichoke may comprise the bulk of the diet of California voles and in part explains the severity of the damage they often cause. The reasons for apparent seasonal dietary shifts are discussed.

Chapter 6 – Vertebrate Pest Control Chemicals and Their Use in Urban and Rural Environments

Publisher Summary This chapter reviews the approaches and techniques used in vertebrate pest management to illustrate and to put into proper perspective the use of vertebrate pesticides compared to other methodologies. Vertebrate pests are a diverse group of animals and include amphibians, reptiles, birds, and mammals. Most wildlife species are considered pests only in relatively few circumstances and may be neutral or highly desirable in most situations. Some of the many types and situations of vertebrate pest problems are referenced, establishing the basis for the use of vertebrate pest control chemicals, both nontoxic repellents and lethal agents. Vertebrate pesticides are targeted to very specific habitats or to only the offending animals or populations. For example, when rodenticides are used efficiently for long-term population suppression, only small amounts of pesticides are needed. Control strategies are selected to be as target specific as possible, using the minimal amount of pesticide. A variety of approaches are employed, including exclusion by fencing, netting, or rodent and bird proofing of buildings; habitat modification; selective crop cultural practices that include resistant crop varieties; and pest-frightening methods. The scope and magnitude of vertebrate problems affect a wide and varied range of activities and health issues. Vertebrate pesticides are represented by two major groups of agents, the lethal or toxic compounds selected or developed for killing the pest animal and the chemical repellents that are used to discourage pests from feeding or gnawing on some item or to repel them from a particular area.

CHAPTER 7 – Vertebrate Pest Control Chemicals and Their Use in Urban and Rural Environments

Vertebrate pest control is used to control vertebrate pests, including amphibians, reptiles, birds, and mammals that have an adverse effect on human health and well-being or conflicts in some significant way with human activities or interests. This chapter focuses on chemicals, approaches, and techniques used in vertebrate pest management. Vertebrate pesticides are represented by two major groups of agents: the lethal or toxic compounds selected or developed for killing the pest animal and the nontoxic chemical repellents that are used to discourage pests from feeding or gnawing on some item or to repel them from some particular area. Chemical repellents are extensively employed in an attempt to manage certain vertebrate pests such as deer, rabbits, rats, dogs, snakes, bats, and a wide variety of others. Based on the mode or modes of action of active ingredients of repellents, they can be are categorized as: predator-like odors, intense novel odors, irritants, distasteful substances, and taste-aversive conditioners. The chapter provides information on toxic vertebrate control methods such as poison rodent baits, glue boards, livestock protection collar, toxic bird perches, fumigants, and toxic tracking powders. Toxic vertebrate pesticides are inherently hazardous because they are developed or selected for their ability to kill pest birds and mammals, which are biologically more similar to humans than to other categories of pests such as insects or nematodes.