Directional acoustic radiation in the strut display of male sage grouse Centrocercus urophasianus

We present evidence that the acoustic component of the strut display of mal e sage grouse Centrocercus urophasianus is highly directional and that the nature of this directionality is unique among measured vertebrates. Where v ertebrate acoustic signals have been found to be directional, they rare mos t intense anteriorly and are bilaterally symmetrical. Our results show that sage grouse acoustic radiation (beam) patterns are often asymmetric about the birds' anterior-posterior axis. The beam pattern of the 'whistle' note is actually strikingly bilobate with a deep null directly in front of the d isplaying bird. While the sage grouse display serves to attract potential m ates, male sage grouse rarely face females head on when they call. The resu lts of this study suggest that males may reach females with a high-intensit y signal despite their preference for an oblique display posture relative t o those females. We characterized these patterns using a novel technique th at allowed us to map acoustic radiation patterns of unrestrained animals ca lling in the wild. Using an eight-microphone array, our technique integrate s acoustic localization with synchronous pressure-field measurements while controlling for small-scale environmental variation in sound propagation.