Remnant trees increase bat activity and facilitate the use of vineyards by edge-space bats

Abstract

Conversion of natural habitats to vineyard monoculture is rapidly increasing both globally and on the California central coast. Although agricultural expansion typically decreases species diversity and abundance, landscape heterogeneity can maintain biodiversity, ecosystem function, and provide pest control services within agricultural systems. Large remnant oak trees are sometimes retained within vineyards, yet little is known about their value to biodiversity or the beneficial services to grape growers. While insectivorous bats (order: Chiroptera) are natural predators of agricultural pests and commonly utilize trees for foraging and roosting, no study has quantified the influence of remnant trees within vineyards on bat abundance and diversity. During 2014 and 2015, we recorded bat activity and species richness as well as insect abundance at isolated remnant trees and paired open areas within 14 vineyards in coastal central California. We used generalized linear mixed models to assess the influence of remnant trees on total and species-specific bat activity and insect abundance, and how these effects were influenced by individual tree and landscape-scale characteristics. We recorded 11,465 bat passes representing 11 bat species. Overall, bat activity rates were 1.5 times greater at trees compared to open areas. Activity levels of low-frequency echolocators adapted to open habitats did not differ between trees and open areas; however, activity levels of high frequency echolocators adapted to edge habitats were 2.4 times higher at trees than open areas. Bat activity at trees increased with larger tree size, closer neighboring remnant trees, and lower remnant tree density in the surrounding landscape. Our study indicates that remnant trees within vineyards provide important habitat value for bats at the landscape-scale by allowing edge-space adapted bat species access to vineyards. Retention of individual large trees can help to maintain biodiversity and ecological function in vineyard landscapes, a benefit for both conservation and agricultural production.