Bats use topography and nocturnal updrafts to fly high and fast

During the day, flying animals exploit the environmental energy landscape by seeking out thermal or orographic uplift, or extracting energy from wind gradients.1–6 However, most of these energy sources are not thought to be available at night because of the lower thermal potential in the nocturnal atmosphere, as well as the difficulty of locating features that generate uplift. Despite this, several bat species have been observed hundreds to thousands of meters above the ground.7–9 Individuals make repeated, energetically costly high-altitude ascents,10–13 and others fly at some of the fastest speeds observed for powered vertebrate flight.14 We hypothesized that bats use orographic uplift to reach high altitudes,9,15–17 and that both this uplift and bat high-altitude ascents would be highly predictable.18 By superimposing detailed three-dimensional GPS tracking of European free-tailed bats (Tadarida teniotis) on high-resolution regional wind data, we show that bats do indeed use the energy of orographic uplift to climb to over 1,600 m, and also that they reach maximum sustained self-powered airspeeds of 135 km h−1. We show that wind and topography can predict areas of the landscape able to support high-altitude ascents, and that bats use these locations to reach high altitudes while reducing airspeeds. Bats then integrate wind conditions to guide high-altitude ascents, deftly exploiting vertical wind energy in the nocturnal landscape. •European free-tailed bats use uplifting winds to ascend 1,600 m above ground level•High-elevation ascents are predicted by geography with high orographic uplift•European free-tailed bats can fly at self-powered airspeeds over 130 kmh−1•Bats deftly exploit nocturnal energy landscapes similar to diurnal birds O’Mara et al. use high-resolution GPS tracking and atmospheric models to show that, similar to diurnal birds, European free-tailed bats use uplifting winds generated by the nocturnal energy landscape to rapidly ascend over 1,600 m above ground level and achieve maximum self-powered airspeeds over 130 kmh−1.