EXPERIMENTAL POPULATION SUPPRESSION OF RICHARDSON'S GROUND SQUIRRELS (Spermophilus richardsonii) IN ALBERTA

Richardson's Ground Squirrel is one of the most economically harmful rodents in east central Alberta. In an effort to develop an effective, safe, economical and practical method of long-term population control over large areas, experimental f i e l d t e s t i n g was begun in 1970 to evaluate a variety of potential control techniques. Although tests w i t h a machine b a i t applicator proved unsuccessful due to the u n i q u e s o i l structure, its potential in other areas of the province is discussed. Use of portable b a i t i n g stations is l i m i t e d by the manufacturing and maintenance costs as w e l l as the l i m i t e d attractabi1ity of the stations. Attractabi1ity of the stations to ground s q u i r r e l s was not increased w i t h the use of reflector tops however it d i d have a repellent influence on raptors feeding in the area. Disposable b a i t i n g tubes appeared to have greater potential for large acreages and p o ss i bl e aerial application. I n i t i a l tests conducted w it h diethylstilbesterol and mestranol as chemosterilants are outlined. The potential of u s i n g techniques to regulate reproductive rate as opposed to increasing mortality rate is discussed. The potential of u s i n g amphetamines to reduce body weight and increase winter m o r t a l i t y d u r i n g hibernation is also discussed. Because of its exceptionally h i g h d e n si t ie s at the present time the Richardson's Ground Squirrel (Spermophilus richardsonii) is currently one of the most economically harmful rodents in east central Alberta (Biggs 1970; Yaremko 1971). Through its burrowing and feeding h ab it s this species has become a pest of s i g n i f i c a n t concern to a g r i c u l t u r i s t s of that area and, in response to requests for assistance, steps were i n i t i a t e d in 1969 to (a) determine the extent and severity of the problem and (b) determine the f e a s i b i l i t y of conducting a range-land population suppression program in that area. Conventional methods of control are often c r i t i c i z e d by n a t u r a l i s t s , conservationists, because of the hazard to local populations of protected raptors. There is a lack of any s i g n i f i c a n t influence on the rodent population from natural predators. Also h i g h d e n s i t i e s of ground s q u i r r e l s in t h i s area present the p o s s i b l e re-occurrence of an outbreak and spread of Alberta Rocky Mountain Spotted Fever and S y l v a t i c Plague (Brown et al. 1943). Several researchers have indicated the shortcomings of u s i n g methods designed to effect population control by increasing m o r t a l i t y rate, as opposed to the advantages of c o n t r o l l i n g population d e n s i t i e s by m a n i p u l a t i n g the reproductive potential of the population (Marsh and Howard 1969; Marsh and Howard 1970; Balser 1964b; Brooks and Bowerman 1969; Howard 1967a; 1967b; 1968; P i n g a l e et al. 1967; Skinner 1968; Srivastava 1966; Weatherbee 1964). After reviewing a l l aspects of the problem, it seemed that the most practical and promising approach to satisfactory long-term, large-area control had already been theorized by Marsh and Howard (1970): to e s t a b l i s h and evaluate an integrated program which would u t i l i z e toxicants a p p l i e d as selectively as possible for an i n i t i a l reduction of "hot spots" of ground squirrel concentrations, followed by larger scale aerial a p p l i c a t i o n of chemosterilants to keep the population at an economically tolerable level. D u r i n g the summers of 1970 and 1971 attempts have been made to (a) develop and evaluate economical and selective methods of a p p l y i n g toxicant b a i t s (b) f i e l d test and evaluate the potential of diethylsti1besterol and mestranol as chemosterilants (c) determine the potential of a r t i f i c i a l l y increasing mortality of females d u r in g hibernation by using fall application of amphetamines (d) monitor other members of the w i l d l i f e food c h a i n for detrimental effects attributable to control measures.