Noisy Gibbons are Black

   Yes, they are fascinating creatures.  Having found a few YouTube videos of the mat-
ing pairs doing their territorial duets, I'm amazed at how they coordinate their calls. 
It seems that the male tries to get the female to begin a series which she repeats with
increasing frequency, at some point interjecting himself to make her stop.  This is
usually done just before they swing through the branches making a few quick calls to
close out the ritual.