Laura Erickson's For the Birds

I’ve never seen this species, but it made the Guinness Book of World Records!

Black Jacobin: Highest-pitched call for a bird. The bird with the highest-pitched call is the black Jacobin hummingbird Florisuga fusca, native to the mountains of the Brazilian Atlantic Forest. A new scientific study published in March 2018 revealed that its most common vocalisations consist of a triplet of syllables with high fundamental frequency (mean F0 ∼11.8 kHz), rapid frequency oscillations, and strong ultrasonic harmonics, and no detectable elements below ∼10 kHz. Indeed, their frequency range is so high that it is above the known hearing range of any bird species currently recorded, even including hearing specialists such as owls. These observations indicate that black Jacobins either have an atypically high frequency hearing range or, alternatively, their primary vocalisation has an as-yet-unknown function unrelated to vocal communication.

This hummingbird’s secret vocalisations were first discovered by neuroscientist Dr Claudio Mello, who had observed black Jacobins in the wild opening and closing their beaks in the same manner that other hummingbird species did when singing, but he couldn’t hear any sounds emerging from the black Jacobins’ beaks. Only when he employed specialized recording equipment normally required to detect and record the ultrasonic squeaks of bats was he able to confirm that they were indeed singing, but at a pitch beyond the upper threshold of human hearing and also above the pitch of all calls previously documented from birds. Mello believes that its incredibly high-pitched calls may give the black Jacobin hummingbird a private line of communication in a noisy forest that is home to 40 other hummingbird species.