We went to the Woodland Park zoo this weekend on a sunny, relatively warmer day, and once again visited the Siamang enclosure (see blog on 1/8/09). When we got there, the female was busy nibbling on a carrot and not very interested in people. Rafe waited for the loud screamy kids to pass by, then crouched down again at the glass.
At first the female didn't seem to notice him. So Rafe hopped a little to get her attention. She stopped mid-bite to look at him. Rafe hopped again. She shook. He shook back. She dropped her carrot and carefully bipeded her way across the branches to the glass towards Rafe. They looked at each other. Then she turned her back. He groomed. It was deja vu all over again.
Unfortunately this time when Rafe turned around and presented his back to her she didn't groom him, but the fact that we could repeat the same event as before is pretty cool. We were able to ask some volunteers if they'd ever seen any behavior like that before, and they said they had seen a little girl play a mirror-type game with the male (she'd jump, he'd jump; she'd wave her arms, he'd wave his arms), but never anything like that with the female.
Still pretty amazing proof in both the male and the female siamang that they can pretend/play/imagine.