If there's one animals we most certainly will never capture with our forest cams, it is the siamang. This ape lives in groups high up in the trees, and as far as I know it does never come down to the forest floor. Attempts to film siamangs with a normal camera always ends up in a disappoinment, because they are shy and move through the canopy with an amazing speed.
However, I do have some recordings of their impressive call, which is very loud and can be heard from many miles away.
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Sound of the Siamang by sounds of leuser