I observed hylobatids and atelids always walking orthograde bipedally while seeking, carrying, dropping and eating bird eggs. At no other time did the spider monkeys walk bipedally. The siamangs always walked bipedally but occasionally pressed one wrist
on the ground while pivoting around corners.
https://www.youtube.com/watch?v=8UaidTfvgRQ
Seeking and carrying eggs.
--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)