A siamang inflating his gular sac during a territorial display. (click here)
Photo (c) 2006 Melissa Barton
Both male and female siamangs have these “gular sacs” on their necks, which they can inflate to the size of their heads to produce resonating calls. Even through the fairly soundproof glass of the enclosure, these calls are loud. The pair started off in unison, alternating between a resonating bark and a sort of mournful wail (a little like elk bugling). As they called, they swung about wildly and stomping on the glass — while staying in perfect vocal unison!
The keepers told us that this is a territorial display, and secondarily, a bonding ritual for the pair. Sometimes a keeper hosing down the enclosure too loudly will set them off, but most of the time the displays seem to be prompted by instinct (there are no other siamangs at the zoo). Captive lions also make territorial calls, although theirs are prompted by sunrise and sunset.
I’m impressed that the tiny baby isn’t deaf yet.
