California voles (Microtus californicus) are a major prey resource for many raptor species. Determining vole population size has traditionally been done with mark-recapture using Sherman traps but this method is very invasive. Several less invasive techniques have been tried but proven to be unreliable. We tried to use toothpick obstructions to block runways and use obstruction clean up rates to determine population size. These obstructions proved to be unreliable due to the voles going around the obstructions and the rate of obstruction removal was variable.