When Jim eventually returned with the canoe, we made our way two or three miles upstream and then landed to reconnoitre the forest to see it if would be suitable for the shots we had in mind. We had hardly gone more than a couple of hundred yards through the trees when to our right, on the crest of a hill, there broke out a cacophony of wild cries. Although basically similar to the gibbon’s call, they were much louder and deeper and each cry ended in an odd, reverberating sound like somebody tapping on a drum with their fingertips.

‘Siamang!’ said the boatman, and Chris’s eyes gleamed fanatically.

‘Let’s see if we can get close enough to try and get some shots of them,’ he whispered.

We made our way cautiously up the little hill, trying to make as little noise as possible, but when carrying cumbersome equipment and surrounded by plants very heavily endowed with spikes and hooks, our progress was anything but silent. However, it seemed that the siamangs were far too concerned with their choral practice to worry about us, for they sang continuously as we approached the trees in which we judged them to be. Just as we thought that we should be getting within sight of them, the singing stopped abruptly and the forest, by comparison, became so silent that our progress through the undergrowth sounded like the approach of a couple of madcap tanks. Suddenly the boatman halted and pointed up into the trees with his machete.

‘Siamang!’ he said again, with an air of great satisfaction.

Some seventy feet above us, in the crown of a rather elegant tree, sat a group of five siamangs. There was an adult male and female, two half grown ones and one baby. Their coal black fur gleamed in the sun and they were sitting nonchalantly on the branches with their long arms and slender hands drooping languidly. It was the arrangement of the group that interested me: the male was sitting on a large branch facing the other four animals, who sat in a row on a branch a little below him and some twelve feet away. It looked exactly as though he was about to give a short and erudite lecture on early siamang music. In case we should flatter ourselves that we had crept up on him unobserved, he periodically glanced down at us and raised his eyebrows as though he found our sweaty and dishevelled appearance somewhat distasteful. Eventually he seemed to get used to the idea that we had come to join his audience, so he turned his attention back to his family. Watching him through fieldglasses, I saw him shuffle his bottom on the branch to get more comfortable, and then he opened his mouth and started to sing.

The first three or four cries were short and staccato, and the effect upon his throat was fascinating. With each cry his throat inflated more and more as he pumped air into his extraordinary gular sac which, as it inflated, gleamed fiery pink beneath his fur. When it was large enough to please him, he launched into the song proper and it was interesting to note that at the end of each verse, as it were, his sac would start deflating until the next verse pumped air into it again. It was obviously this strange vocal sac that produced the odd, drum-like tapping  at the end of each verse, and I could only presume it was made by the sound of air being expelled from this soundbox. As soon as he had finished his song there was a short pause, while his family, who had been listening with rapt attention, gazed at him fixedly. Then the big female, one of the smaller ones, or occasionally even the baby, would utter a series of high-pitched staccato cries that sounded rather like applause and were presumably accepted as such by the male, for he would react to it by launching himself into yet another verse of his song. This went on for about a quarter of an hour, the family group inciting him to sing more every time he stopped, and each time he sang he displayed more and more symptoms of excitement; it was rather like watching a pop singer working himself up to a final burst of song for his fans. First he started reaching out with his long arms and snapping off leaves from the surrounding branches; then he bounded up and down on his bottom and the family’s applause became even more vociferous. Carried away by this, his next action was to run up and down the branch, his arms crooked and his hands dangling in that lovely pansy way that gibbons have; the family group grew positively ecstatic over this.  Now he came to his finale and launched himself in a flying leap from the branch, dropped about thirty feet like a stone, his arms and legs completely relaxed and then, as you were almost sure he was hurtling to his doom, with a casual air he reached out a long arm, grabbed a passing branch, and swung there like a black, furry pendulum, singing his heart out.

Watching this grave, but obviously happy choir of siamangs, gave me immense pleasure. They clearly took their music very seriously and enjoyed every minute of it. It was nice to feel that in that enormous section of protected forest there would always be groups of siamangs singing happily to each other in the bowers of green leaves.