Reproductive behaviors such as mounting and copulation calls spread through gull breeding colonies via social facilitation. We showed that broadcasts of model copulation calls to breeding Glaucous-winged Gulls (Larus glaucescens) did not increase the overall numbers of bouts of head tossing or mounts, but they did coordinate the timing of subsequent head-tossing and mounting behaviors. By contrast, silent controls and non-gull sounds with similar spectral features and duty cycles did not coordinate the timing of either head tossing or mounts. Disturbances by humans, such as those occurring during an egg census, caused increases in head tossing in the short term but did not affect the number or timing of mounts. Eagle disturbances reduced the frequency of head tossing and mounting overall, and coordinated the timing of head tossing but on a longer time scale compared to the effect of a human disturbance. Our data demonstrate that the copulation call, without associated wing-flagging, is sufficient to cause the socially facilitated coordination of these reproductive behaviors in gulls, whereas other stimuli do not.

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