Male nestling-like courtship calls attract female barn swallows, Hirundo rustica gutturalis

• Males often behave like nestlings at courtship, at least from a human perspective.
• We experimentally tested this argument by using barn swallows.
• We showed the objective similarity of male courtship calls and nestling calls.
• Females were attracted similarly towards these calls during the courtship period.
• Males would mimic nestlings to attract female attention.

Courtship behaviours of males often resemble the food-begging behaviour of their young, at least from a human perspective. Although it is argued that this represents a sensory trap, it is still unclear whether such behaviour in males is objectively similar to nestling behaviour and can elicit female parental care (e.g. attraction to nestlings) in courtship, as predicted by the sensory trap hypothesis. In this study, we demonstrated that the enticement calls of male barn swallows structurally resemble the food-begging calls of nestlings, compared with the other three male vocalizations (i.e. songs, alarm calls and contact calls). In addition, we used experimental playback of the vocalizations to compare the response of females towards male enticement calls and nestling food-begging calls during the courtship period. We found that females were attracted to the playback of nestlings' food-begging calls during the courtship period, despite nestlings being absent at this time. The response of females to food-begging calls was similar and positively correlated with their response to male enticement calls. These observations support the sensory trap hypothesis, i.e. that male signals mimic stimuli to which females respond for parental care.