Fig. 4. Amplitude measurements (means ± S.E.M.) at a recording distance of 100 m in four transmission habitats and at three recording heights. At this distance, attenuation due to spherical spreading alone theoretically results in an amplitude of 56.4 dB. Species are grouped according to their native habitats. Letters above error bars (a–c) indicate significance individually within each plot, with different letters representing a significant difference at the 5% level and the same letter indicating no significant difference.