The reason for the high frequency portion of the bugle is due to the propagative efficiency of differing frequencies through varying environments. Studies have shown that as a bull's harem increases in diameter, meaning the cows become more dispersed, he tends to vocalize more frequently than if they were within closer proximity. The higher-pitched section of the call propagates through the environment better which is why the bull uses it to congregate a harem that is becoming more spatially dispersed and thus harder to defend. Acoustic analyses comparing bull elk bugles with cow elk cohesion calls show a notable degree of acoustic similarity, indicating that both vocalizations may perform a congregating function, which is why the bugle is often used by the bull to condense his harem.