Private Number Calls Cell Phone Then Hangs Up

[sooner333]

Does this happen to anyone else? I've gotten a few calls from an unknown or private number the past few days. First time I've had the opportunity to pick it up was today and I heard almost a bird chirp and then it hung up. Anyone else have this happen to them?

[Honolulu_Blue]

It's probably this guy. He's quite the prankster...

http://www.comedycentral.com/tosh.0/files/2009/12/bird-calls-home.jpg

[CU Tiger]

There are some questionable tm practices that employ random dial, an answers confirms it is a valid number and adds it to a database...