Whooping monkeys

The siamangs were at it again this morning, and I always wonder what is driving their vocalizations. They're way up on Phinney Ridge, in the Woodland Park Zoo, over a mile away, and their whoops really carry. Sometimes you can hear them during softball tournaments, as if they were joining the fans in the bleachers. Other times it seems to be related to a full moon. This morning, perhaps they were expressing appreciation for the cool cloud cover and invigorating air.
I stopped by our vet's to pick up the cat carrier I had left for our cat to use for the brief remainder of his existence. His little old blue collar had been tucked inside.