Swiftlets
Another interesting feature of these birds is their echo-location. They are particularly amazing by being able to find exactly where their nest is amongst the numerous other nests surround their own. I suppose it isn't a pleasant experience because their echo-location is audible to humans.
Wikipedia says:
The genus, Aerodramus was thought to be the only echolocating swiftlets. These birds use echolocation to locate their roost in dark caves. Unlike a bat’s echolocation, Aerodramus swiftlets make clicking noises that are well within the human range of hearing. The clicks consist of two broad band pulses (3-10 kHz) separated by a slight pause (1-3 milliseconds). The interpulse periods (IPPs) are varied depending on the level of light; in darker situations the bird emits shorter IPPs, as obstacles become harder to see, and longer IPPs are observed when the bird nears the exit of the cave. This behavior is similar to bats as they approach targets. The birds also emit a series of low clicks followed by a call when approaching the nests; presumably to warn nearby birds out of their way. It is thought that the double clicks are used to discriminate between individual birds. Aerodramus sawtelli, the Atiu Swiftlet, and Aerodramus maximus, the Black-nest Swiftlet are the only known species which emit single clicks. The single click is thought be used to avoid voice overlap during echolocation. The use of a single click might be associated with an evolutionary shift in eastern Pacific swiftlets; determining how many clicks the Marquesan Swiftlet emits, could shed light on this.
I hope I didn't swiftlet you guys down!
Wikipedia says:
The genus, Aerodramus was thought to be the only echolocating swiftlets. These birds use echolocation to locate their roost in dark caves. Unlike a bat’s echolocation, Aerodramus swiftlets make clicking noises that are well within the human range of hearing. The clicks consist of two broad band pulses (3-10 kHz) separated by a slight pause (1-3 milliseconds). The interpulse periods (IPPs) are varied depending on the level of light; in darker situations the bird emits shorter IPPs, as obstacles become harder to see, and longer IPPs are observed when the bird nears the exit of the cave. This behavior is similar to bats as they approach targets. The birds also emit a series of low clicks followed by a call when approaching the nests; presumably to warn nearby birds out of their way. It is thought that the double clicks are used to discriminate between individual birds. Aerodramus sawtelli, the Atiu Swiftlet, and Aerodramus maximus, the Black-nest Swiftlet are the only known species which emit single clicks. The single click is thought be used to avoid voice overlap during echolocation. The use of a single click might be associated with an evolutionary shift in eastern Pacific swiftlets; determining how many clicks the Marquesan Swiftlet emits, could shed light on this.
I hope I didn't swiftlet you guys down!