The localization of acoustic signals is an important component of mating behaviour in many species.
However, in natural environments sound localization may be hindered by background noise that masks
acoustic cues that enable the determination of sound direction by the auditory system. I studied the
effects of noise on the sound localization abilities of male grasshopper, Chorthippus biguttulus, in
response to female songs. Males respond to female songs with a stereotyped lateralization behaviour in
which they turn towards the perceived sound direction; repetition of this behaviour allows them to
approach females. Under quiet conditions, males are highly sensitive to small differences in the timing or
amplitude of signals that arrive at each ear. I tested whether noise affected male lateralization accuracy
by presenting males with female songs that differed in time or amplitude cues of sound direction, under
different levels of masking noise. Noise sharply reduced the responsiveness of males to female songs.
However, when males did lateralize the female song, they were surprisingly accurate, even at the highest
noise levels. These results suggest that noise only weakly impairs males' directional hearing abilities, but
strongly affects their abilities to detect and respond to female songs. Noise therefore probably increases
mating costs, because both males and females must expend additional time and energy in mate attraction.