The earth is now subject to climate change and habitat deterioration on unprecedented scales. Monitoring climate change and habitat loss alone is insufficient if we are to understand the effects of these factors on complex biological communities. It is therefore important to identify bioindicator taxa that show measurable responses to climate change and habitat loss and that reflect wider-scale impacts on the biota of interest. We argue that bats have enormous potential as bioindicators: they show taxonomic stability, trends in their populations can be monitored, short-and longterm effects on populations can be measured and they are distributed widely around the globe. Because insectivorous bats occupy high trophic levels, they are sensitive to accumulations of pesticides and other toxins, and changes in their abundance may reflect changes in populations of arthropod prey species. Bats provide several ecosystem services, and hence reflect the status of the plant populations on which they feed and pollinate as well as the productivity of insect communities. Bat populations are affected by a wide range of stressors that affect many other taxa. In particular, changes in bat numbers or activity can be related to climate change (including extremes of drought, heat, cold and precipitation, cyclones and sea level rise), deterioration of water quality, agricultural intensification, loss and fragmentation of forests, fatalities at wind turbines, disease, pesticide use and overhunting. There is an urgent need to implement a global network for monitoring bat populations so their role as bioindicators can be used to its full potential.

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Roads illuminated by white streetlamps attracted three times more foraging bats (mostly Pipistrellus pipistrellus) than did roads lit by orange streetlamps or unlit roads (3.2, 1.2 and 0.7 bat passes/km, respectively). More insects flew around white lamps than around orange lamps (mean 0.67 and 0.083 insects per lamp, respectively). The mean number of bat passes recorded in any 1‐km section of road was positively correlated to the number of white streetlamps along the section, and also, independently, to the amount of trees and hedgerows. Bat activity was not related to the number of houses along the road, ambient temperature or cloud cover. The attractive effect of the lamps on the bats was diminished in windy weather.