Did you notice if they were shut out on it? Despite plenty of vegetation on the Mountain nowadays I believe they still prefer to stay indoors most of the time so in good weather they scatter feed them on here and shut the door from the old enclosure.
Yes, they were using the indoor section and the old paddock when I arrived at 10. There was a scatter feed on the island at about 11.30 and I think the doors to the house were locked at about the same time - they weren't very inclined to stay on the island when they had cleared up the food, but it was quite breezy and the glass windows probably made the paddock warmer.
I went off to look at the rest of the zoo at about 12. When I went back at about 3 they were locked on the island, and they were only allowed back at about 3.30 pm, when they headed inside the house, Bukavu came down the hill after the females but at the run - too fast for me to get a decent photo I'm afraid.
While they were on the island the females kept walking round the 'shoreline' while Bukavu stayed near the top. I was lucky to catch him in this pose, he didn't hold it for very long.