Bat activity at remnant oak trees in California Central Coast vineyards

Abstract

During 1990 to 2013, the area planted with wine grapes increased nearly 4.5 times in San Luis Obispo County. Much of this development occurred on open oak savanna with scattered oak (Quercus spp.) trees. Remnant trees are retained in some vineyards, but their value to biodiversity retention has not been quantified. During April to September 2014, at six vineyards in San Luis Obispo County, we compared echolocation activity of bats and the abundance of insects at remnant trees to locations without trees in the vineyards. The mean number of insects per night was over two times greater at vineyard trees. We recorded 3,677 bat calls at vineyard trees compared to 1,070 bat calls at open vineyard sites. Calls characteristic of bats that forage around trees were almost exclusive to trees (97 percent of high frequency calls), compared to calls of open-space bats, which were similar at both site types (57 percent of low frequency calls at trees vs. 43 percent in open vineyard). These findings indicate that large remnant oak trees in vineyards not only support higher levels of bat activity, but also increase the diversity of bats that occur and forage in the vineyard. This small-scale study lays the framework for addressing larger, more complex questions surrounding the benefits of remnant trees for bats and the ecosystem services they provide to grape growers.

Parent Publication

• Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world

Citation

Tietje, William D.; Weller, Theodore J.; Yim, Christopher C. 2015. Bat activity at remnant oak trees in California Central Coast vineyards. In: Standiford, Richard B.; Purcell, Kathryn L., tech. cords. Proceedings of the seventh California oak symposium: managing oak woodlands in a dynamic world. Gen. Tech. Rep. PSW-GTR-251. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 97-106.