End-year
progress
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Damage and population densities were assessed at 8 sites in Butte Valley, Siskiyou County; and at eight sites in Surprise Valley, Modoc County. Data on yield losses for one site in Butte Valley and four sites in Surprise Valley were lost as a result of the fields being taken out of production. Losses ranged from 9 to 40% (mean = 27.0%) in Butte Valley, and from 0 to 55% (mean = 26%) in Surprise Valley. There was no significant difference in yield loss between counties, nor a significant change in damage from the previous year of the study. At current market value of $110 per ton (dry weight alfalfa), these losses equate to a dollar loss of $78 per acre of alfalfa. At all sites, initial squirrel population densities increased from the previous year. Sites supported a mean of 54 squirrels/ha in February 1999 compared to only 17 squirrels/ha in February 1998. Juveniles were observed in April 1999 when populations peaked at between 21 and 53 squirrels per acre. Fences made from a relatively inexpensive erosion control fabric have been marginally successful in reducing squirrel invasion into new fields. However, they have been expensive to maintain and may therefore not be practical. Problems have mostly been due to meadow voles making holes in the material, thus providing entry points for squirrels. Vegetation control alongside the fences is also more difficult and must be done with herbicides rather than mechanical methods (mowing of burning) preferred by growers. This research has resulted in one peer-reviewed publication and another is in preparation. Results have also been presented at the annual meeting of WCC-95: Vertebrate Pests of Agriculture, Forestry and Public Lands.
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