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Scientists Collaborate to Bring Insectivorous Bats into the Vineyard

The Issue

Across the highly modified agricultural landscape, remnants of native plant cover are necessary to sustain biodiversity and ecological functions. Valley oak trees are key plant structures that have been retained in some newly developed vineyards in San Luis Obispo County. Historically, many of these majestic giants were removed to make way for development. Today, their populations are greatly reduced and the remaining valley oaks are not regenerating. The loss of the many ecological functions, ecosystem services, and the beauty that the iconic trees provide is of great concern to the agriculturalist, environmentalist, and general public. For example, insectivorous bats are known to utilize large trees for foraging, predator protection, roosting, and reproduction. Bats are beneficial because they feed on insect pests that cost farmers billions of dollars annually in lost production! Unfortunately, many species of bats are threatened by habitat loss and disease. Some species are declining alarmingly. Could the lone tree within the vineyard offer insectivorous bats these essential functions?

What Has ANR Done?

A collaborative study by UC and US Forest Service, Pacific Southwest Research Station, scientists is examining the habitat value to insectivorous bats of the remnant valley oak tree within the vineyard. Fourteen cooperating grape growers in San Luis Obispo County are helping scientists answer this question. In each of the vineyards, we set up bat echolocation-call recorders, one at the tree and one 100 meters from the tree within the open vineyard. At the tree and the no-tree sites, we also erected an insect trap to assess insect abundance.

The Payoff

Research demonstrates that the iconic valley oak brings insect-eating bats into the vineyard

We recorded 11 species of insectivorous bats within the vineyards. Over 2.5 times more of the bat calls were recorded at the trees than in open vineyard. Of the recordings, a group of bats adapted specifically to treed habitat (woodland bats or edge-adapted bats) was recorded nearly 11 times more at trees than in the open vineyard. Indeed, over 90% of this group’s echolocations were at trees. Our data indicate that a large oak tree attracts insectivorous bats to the interior of a vineyard. Importantly, the trees attracted a group of woodland or edge-adapted bats to the interior of the vineyard that would not have been within the vineyard if not for the tree. Similar numbers of insects were trapped at the trees and in the open vineyard, suggesting that in addition to insect foods, other habitat features of the oak tree are important to the bats. For example, the bats could be attracted to the trees for preferred insect foods, protection from predators, improved foraging conditions, and for roosting. Further research is warranted to answer these questions, and whether a tree that provides bat habitat could also help growers keep populations of night-time insect pests in check and potentially reduce the use of chemical pesticides.


Supporting Unit: San Luis Obispo County

Bill Tietje, Wildlife Extension Specialist, Department of Environmental Science, Policy, and Management (ESPM), UC Berkeley tietje@berkeley.edu; Anne Polyakov, Data Analyst, ESPM UC Berkeley; Ted Weller, Ecologist, US Forest Service, Pacific Southwest Research Station tweller@fs.fed.us