SIPORA, Indonesia—At the top of a tumung tree, the black shadow of a bilou hides behind a thicket of leaves. Its long arms hug the branches. Its black eyes watch us below, on the red, clay road of the newly cleared forest.
The pygmy siamang, one of the endemic primates of the Mentawai Islands, is slender with shiny black fur.
Bilou is renowned for the sonority of his screech every morning. The high, melodious screech has been dubbed the most beautiful rhythm emitted by a mammal.
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Bilou is also considered the most primitive type of ungko because of its simple screech that is thought to resemble the screech of the ungko's ancestors. But that morning, the bilou did not make a sound.