Female birds prefer males with higher-pitched calls?
From Purdue University:
Andrew DeWoody, a Purdue University professor of genetics, found that the higher the pitch of a male bird's song, the more genetic diversity that bird has, making him a better mate for breeding. His study was published Wednesday (Dec. 2) in the early online edition of PLoS One. ...DeWoody said females might choose the males with higher-pitched calls because of potentially greater genetic diversity in their offspring. You can listen to Ocellated Antbird calls and see photos at Xeno-canto.org
The antbirds have several calls, some to let fellow antbirds know where the army ants are heading, others to attract mates and still others that are defensive or aggressive to protect turf. DeWoody's research involved recording those calls and matching them to DNA samples of the birds. The results suggest that genetic diversity in antbirds affects their physical abilities to produce certain sounds.