Summary1. Currently, tropical forests are transformed into pasture and agricultural areas at an unprecedented rate, yet converted areas are often abandoned by farmers because depleting soil fertility renders unprofitable any agricultural land use. Natural succession of abandoned land could counter the loss of biodiversity, but the rate of natural reforestation is slow. 2. Neotropical frugivorous bats facilitate natural succession because they seem to tolerate habitat disturbance when dispersing seeds of pioneer plants. Under naturally dark conditions, bats produce a copious seed rain even in deforested habitats and connect distant forest fragments. Yet, artificial light at night may compromise bat-mediated seed dispersal if bats avoid lit areas. This may delay or jeopardize natural forest succession in fragmented tropical landscapes. 3. We asked whether the foraging behaviour of Sowell's short-tailed bats Carollia sowelli, a specialist on infructescences of pepper plants (Piperaceae), is negatively affected by artificial light at night. 4. First, in a dual choice experiment with captive bats, we demonstrate that food was less often explored and consumed in the dimly illuminated than in the dark compartment, indicating that artificial light alters the foraging behaviour of fruit-eating bats. Secondly, using observations in free-ranging bats, we found that infructescences were less likely to be harvested when plants were illuminated by a street lamp than under natural darkness. 5. Synthesis and applications. Natural succession of deforested areas and connectivity of remaining forest patches may suffer due to artificial light at night through a reduction in nocturnal seed disperser activity in lit areas. This could have negative impacts on biodiversity and consequent effects on land erosion, particularly in developing countries of the tropics where light pollution increases rapidly with growing economies and human populations. Mitigation requires that the use of artificial light should be limited in space, time and intensity to the minimum necessary. The effectiveness of 'darkness corridors' to enhance fragment connectivity and to reduce species loss should be evaluated. Policy-makers of tropical countries should become aware of the potential detrimental effects of artificial lighting on wildlife and ecosystem functioning.

While artificial lighting is a major component of global change, its biological impacts have only recently been recognised. Artificial lighting attracts and repels animals in taxon-specific ways and affects physiological processes. Being nocturnal, bats are likely to be strongly affected by artificial lighting. Moreover, many species of bats are insectivorous, and insects are also strongly influenced by lighting. Lighting technologies are changing rapidly, with the use of light-emitting diode (LED) lamps increasing. Impacts on bats and their prey depend on the light spectra produced by street lights; ultraviolet (UV) wavelengths attract more insects and consequently insectivorous bats. Bat responses to lighting are species-specific and reflect differences in flight morphology and performance; fast-flying aerial hawking species frequently feed around street lights, whereas relatively slowflying bats that forage in more confined spaces are often light-averse. Both highpressure sodium and LED lights reduce commuting activity by clutter-tolerant bats of the genera Myotis and Rhinolophus, and these bats still avoided LED lights when dimmed. Light-induced reductions in the activity of frugivorous bats may affect ecosystem services by reducing dispersal of the seeds of pioneer plants and hence reforestation. Rapid changes in street lighting offer the potential to explore

Similar to insects, birds and pterosaurs, bats have evolved powered flight. But in contrast to other flying taxa, only bats are furry. Here, we asked whether flight is impaired when bat pelage and wing membranes get wet. We studied the metabolism of short flights in Carollia sowelli, a bat that is exposed to heavy and frequent rainfall in neotropical rainforests. We expected bats to encounter higher thermoregulatory costs, or to suffer from lowered aerodynamic properties when pelage and wing membranes catch moisture. Therefore, we predicted that wet bats face higher flight costs than dry ones. We quantified the flight metabolism in three treatments: dry bats, wet bats and no rain, wet bats and rain. Dry bats showed metabolic rates predicted by allometry. However, flight metabolism increased twofold when bats were wet, or when they were additionally exposed to rain. We conclude that bats may not avoid rain only because of sensory constraints imposed by raindrops on echolocation, but also because of energetic constraints.