Each bat increased a) echolocation intensity and b) metabolic rate when flying in background noise. The individual increase in metabolic rate averaged 0.05 ± 0.009 ml CO2 g-1 min-1 (range 0.01–0.09 ml CO2 g-1 min-1). c) Pulse durations also increased significantly when bats called louder in high background noise (t = −5.991, df = 8, p < 0.001). Boxes show the median (horizontal line) and interquartile range, whiskers extend to the range of the data. Colours represent individuals, grey lines connect data for individuals.