Female canaries invest more in response to an exaggerated male trait

► We measured the influence of song stimulation on maternal investment in canaries. ► We broadcast three types of songs (average, sexy and supranormal) to female canaries. ► Females exposed to supranormal stimuli laid bigger eggs than other females. ► We found no effect of the type of song on testosterone concentration in the eggs. ► It raises the question of how and why these different investment mechanisms evolved.