The hoolock gibbon is an extremely endangered primate. Measuring less than a metre and weighing about 68kg, the animal is Indias only ape. This tailless primate is known more by its distinctive, haunting song, than by sight. Gibbon songs resound in the Namdapha forests at dawn. Vocalised as a loud hookoo-hookoo, the songs are sung by one group at a time, with other groups taking over in turns. The chorus continues till the sun is high up in the sky.