Bird enthusiasts already know that male hummingbirds do impressive dives to excite potential lady-friends during mating season. But scientists have found that these dives may be more about sound than sight — it turns out that the rapid downward motion causes the male birds' feathers to vibrate, which makes a sound the lady-birds can hear. The females may even be able to detect small differences in tail feathers, allowing them to pick the mate with the best-sounding tail.