Bats respond negatively to increases in the amount and homogenization of agricultural land cover

Abstract

Agricultural intensification has led to widespread declines in biodiversity. An important component of agricultural intensification in many regions, including eastern Ontario, is the shift from grazing lands and perennial forage crops to annual row crops, with associated increases in use of pesticides. We predicted that bat abundance and diversity would be lower in sites surrounded by landscapes with more agriculture and where the agriculture was dominated by annual row crops rather than perennial forage crops. We assessed bat occurrence and relative bat abundance with acoustic bat recorders at the centres of 32 landscapes that varied in (1) the proportion of agriculture and (2) the proportion of agriculture that is in annual row crops versus perennial forages (pasture and hay). Consistent with our first prediction, the abundance or presence of four bat species, total bat abundance and bat species richness declined with increasing agricultural cover in the surrounding landscape. Inconsistent with our second prediction, the abundance of three bat species, total bat abundance and bat species richness were greatest where the proportion of agriculture in annual crops was about equal to the proportion in perennial forage in the surrounding landscape. Based on these results, bat abundance and richness can be increased in agricultural landscapes by reducing the conversion of natural areas to agriculture and by maintaining a balance of perennial forage and annual crop types. We speculate that farmlands with a diversity of crop types provide a more temporally stable supply of insect food for bats.