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Project description

California ground squirrel (Spermophilus beecheyi) foraging behavior: implications for improved control. (01DS017)
Program UC IPM competitive research grants program
T.P. Salmon, Wildlife, Fisheries and Conservation Biology, UC Davis
Host/habitat Unspecified
Pest California Ground Squirrel Spermophilus beecheyi
Discipline Wildlife Biology
Decision Support
Start year (duration)  2001 (Three Years)
Objectives Determine the daily pattern and amount of seed foraging and "effective" feeding home range of California ground squirrels.

Determine the effect of bait density on squirrel foraging behavior.

Determine the optimum baiting area and bait density for delivering a lethal dose of anticoagulants.

Determine the occurrence and extent of non-target bait consumption.

Develop and test a single application baiting strategy for currently registered anticoagulants "that lead(s) to a more judicious use of pesticides".

Final report This project successfully demonstrated that a pest species, the California ground squirrel (S. beecheyi), forages according to central place foraging and optimal foraging theory principles. As toxicant-treated oats are a primary method of control, this information is potentially very useful in the development of more effective, safer and less labor- intensive control methods.

Using the knowledge obtained through investigating S. beecheyi foraging behavior, a potential alternative control method was developed. Conventional control methods require broad area application of toxicant baits with repeated applications. The developed method required only a single application and represented a significant reduction in both labor and in the quantities of toxicant spread into the environment. While the alternative method did not successfully meet the required level of population reduction (70 percent as established by the Environmental Protection Agency), it did demonstrate that a substantial population reduction could be achieved with significantly less pesticide and application effort. Using the knowledge obtained it is hoped that a method that retains the increased environmental safety can be developed that meets the efficacy needs of those in agriculture.

Continuing on research performed in 2002, the efficacy of an alternate anticoagulant control strategy for California ground squirrels (Spermophilus beecheyi) was tested. Research into the foraging behavior of S. beecheyi revealed that a single application of anticoagulant bait should provide similar control as do the current practices of multiple baiting. Such a strategy would reduce the amount of anticoagulant used, resulting in less risk to predators, scavengers and other grainivores that might feed on the bait or poisoned carcasses. In the early summer of 2003, ten sites were selected in the foothills east of Paso Robles, California. These sites were typical cattle grazing areas although no cattle were present during our tests. Of the ten sites, four were randomly selected for the standard control strategy (11.25 kg/ha; 0.01% diphacinone treated oats, applied twice), four for application of the experimental treatment (22.5 kg/ha; 0.005% diphacinone treated oats, applied once) and two as controls (22.5 kg/ha untreated oats). Our results showed that the experimental treatment was less than 70% effective in controlling the squirrel population; a level that is not acceptable under normal circumstances. This spring, we will continue this work to further refine and evaluate this control strategy.

The foraging behavior of the California ground squirrel is being examined under four levels of food supplementation. Supplementing with labeled steam rolled oats (SROs) simulates a baiting program, and allows monitoring of the oat densities to determine rate, location, and timing of foraging. Combining this information with anticoagulant toxicology will allow the possible development of a single application anticoagulant control strategy by adjusting baiting density to the foraging strategy of squirrels. Such a strategy would reduce non-target risks associated with control efforts, as less pesticide would be used.

During the summer of 2002 non-target bait consumption was conducted using surveillance video camera systems placed on the treatment sites. Monitoring was conducted before and after supplementation to determine possible changes in non-target visit rates. No difference was observed between the before and after supplementation. However, it should be noted that this was conducted on sites with single applications. Current use requires a minimum of two applications; this could increase the draw of non-target animals into a baited area.

Preliminary results from 2002 were examined and a potential single feeding strategy was developed. This preliminary strategy was tested on an un-replicated plot in October 2002. Although the single application rate showed efficacious control (approximately 77%) with greatly reduced pesticide use, there were several confounding factors. Results indicate that an effective single feeding strategy may be developed. However, the timing of this application was not optimal. In the next field season more extensive testing of the developed method will be conducted.

The California ground squirrel is a seasonally driven animal. Periods of inactivity occur in late summer and during winter. Diet selection is equally driven by seasonal availability of food. For this reason control with rolled oats as carriers of toxicant occurs exclusively in late spring and early summer when ground squirrels forage upon seeds. This research addresses baiting at this time. Currently it is focused on technique development for the upcoming field season.

The determination of seed acquisition and consumption by ground squirrels will allow the development of a reduced use baiting strategy. To do this we will track the fate of fluorescent-dyed oats dispersed on our plots at various application rates. Testing of the effects of this dye on consumption has been completed and indicates that the dye used, at the treatment concentration, will not affect consumption.

Work also progressed in developing a technique for monitoring oat density. We developed a portable light box with multiple long wave UV lights. With this device, we can easily record oat density in the field. The light box has an opening for the lens of a camera to record the presence of oat groats. The treated oat groats fluoresce under UV light, making oats visible and density easily determined. Field tests of this technique will be conducted in the spring when environmental conditions more resemble those that will be found during testing.

Determination of actual foraging rate and area will commence this spring and summer.

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