Yoki was calling from the first week I brought him home...when the only other frog in sight was his brother, Pip. From what I can gather, the males will call regardless of females around. In the hopes that one might hop out from behind the living room curtains! It really is a beautiful sound, but maybe listen to some audio at top volume so you get used to it. My house has 4 different calls on each given night (Pacific Chorus frogs; Green Treefrogs; Fire Belly Toads; African Giant Bullfrog) and we still manage to sleep. Most nights!