Strychnine baits to control Richardson’s ground squirrels: an old story, a new twist

Author(s): Bourne, John B.; Roy, Laurence D.; Hiltz, Michelle; Merrill, Phillip N.; Hoffmann, Wolfgang | Abstract: We conducted field trials during 2000 to compare the effectiveness of 0.4% strychnine commercial ready-to-use (RTU) hull-less oat and canary seed (CS) bait to control Richardson’s ground squirrels (Spermophilus richardsonii) and during 2001 to compare the effectiveness of RTU and freshly prepared from concentrate (FFC) hull-less oat bait. Each study was conducted at 30 locations in ungrazed pastures and unharvested forage crops in southern and central Alberta from mid-June to mid-August. Effectiveness was measured using pre and post treatment visual, dead and in 2000 active burrow counts. In both trials visual counts increased with daily maximum temperature (P l 0.05), decreased with rainfall intensity (P l 0.001) and were not affected by wind speed or start time (P g 0.05). The 2000 field trials indicated that adjusted visual counts of ground squirrels were significantly lower than controls in CS than RTU baited plots (77.6% and 59.6% reduction, respectively, P = 0.002) and the mean number of dead ground squirrels was higher (6.43 and 2.13, respectively, P l 0.001). Additionally, there were significantly (P l 0.001) fewer re-opened holes by ground squirrels in the RTU (41.6%) and CS (71.7%) treated plots compared to control plots. All 3 measures indicated greater effectiveness using canary seed than hull-less oat bait. The 2001 field trials indicated that adjusted visual counts of ground squirrels were significantly lower than controls in FFC than RTU baited plots (92.7% and 65.6% reductions, respectively, P l 0.0001) and the adjusted mean number of dead ground squirrels was higher (4.28 and 1.21, respectively, P l 0.0001). Both measures indicated greater effectiveness using freshly prepared from concentrate than manufactured ready to use hull-less oat strychnine baits. In conclusion, we advocate further research into freshness as bait freshness may be the single most important factor affecting effectiveness