Orangutan biphonic voiceless + voiced call combinations produced by Bornean flanged males (P. pygmaeus) and Sumatran adult females (P. abelii). A) Spectrographic representation (0- to 40-Hz bandstop filter applied for clarity purposes) of an exemplar case of “chomps + grumbles” by Zeke; dashed boxes highlight general range and profile of chomps (black) and grumbles (white); dashed line (purple) presents time used to extract spectrogram amplitude slice. B) Spectrogram amplitude slice depicting chomp's and grumble's simultaneous frequency maxima. C) Bornean flanged male at Tuanan, Central Kalimantan, Indonesian Borneo (credits: A.R.L.). D) Spectrographic representation of an exemplar case of “kiss-squeaks + rolling calls” by Sina; dashed boxes highlight general range and profile of kiss-squeaks (black), rolling calls (white), and grumphs (gray); dashed line (purple) presents time used to extract spectrogram amplitude slice. E) Spectrogram amplitude slice depicting kiss-squeaks's and rolling call's simultaneous frequency maxima. F) Sumatran adult female at Ketambe, Aceh, Sumatra, Indonesia (credits: M.E.H.).