Male satin bowerbirds, Ptilonorhynchus violaceus, adjust their display intensity in response to female startling: an experiment with robotic females

Females of many species preferentially mate with males that produce courtship displays at a high intensity or rate; however, males do not always display at their maximum intensity during courtship. Evidence suggests that this behaviour may be adaptive in satin bowerbirds, because overly intense displays can disrupt courtship by startling females. Females signal the display intensity that they will tolerate from a male; males that respond by adjusting their intensity reduce the likelihood of startling females and increase their courtship success. However, even the most responsive males occasionally startle females. When this occurs, males could avoid further threat to females by decreasing the intensity of their subsequent displays. We used robotic female bowerbirds that mimicked female startling to test the hypothesis that males reduce the intensity of their courtship displays after startling females. Supporting this hypothesis, males displayed at significantly lower intensity after robots were startled in experimental treatments than when they were not startled in control treatments. We found no evidence that the degree of male response to startling was related to male courtship success. In spite of evidence that female bowerbirds prefer the most intensely displaying males as mates, we found that males did not always display at maximum intensity, but rather reduced their intensity in response to female startling during courtship. Our results suggest that males adjust the level of expression of their display traits in response to female behaviours during courtship, and by doing so, males may increase their chances for successful courtship.

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