Very interesting information, thanks a lot.
In 2004 we wrote (Hum.Evol.19:53-70): "... some birds, such as mockingbirds and parrots, can mimic human speech (Pepperberg 2000) ... The only mammals known so far that can mimic human utterances ... was a harbour seal that had learned to produce (albeit with a throaty voice) fragments of humanlike speech from a fisherman, probably at a sensitive period early in its life (Ralls et al. 1985, Deacon 1997) and to a very limited extent a beluga whale (Eaton 1979)." Your orangutan is another example of such animals.
Your study accords well with our view, based on the "coastal dispersal model" (S.Munro 2010 "Molluscs as Ecological Indicators in Palaeo-anthropological Contexts" PhD thesis Austr.Nat.Univ.). Comparative & physiological data show that Pleistocene Homo did not disperse globally running over open plains as popular & conservative views of human evolution believe, but simply followed the African & Eurasian coasts & rivers (as far as Java & Georgia 1.8 Ma), beach-combing, diving & wading bipedally for littoral, shallow aquatic & waterside foods. Apparently, the combination of Miocene hominoid gibbon-like song production with Pleistocene Homo's shallow aquatic & waterside food collection (breath-hold diving, soft food swallowing, brain expansion) preadapted to human speech, e.g.
M.Vaneechoutte, S.Munro & M.Verhaegen 2011 "Seafood, diving, song and speech"
(pp.181-9 in M.Vaneechoutte et al. eds "Was Man more aquatic in the past?" eBook Bentham Sci.Publ.):
"... comparative data suggest that the various elements of human speech evolved at different times, and originally had different functions. Recent work by Nishimura [1-6] shows that what is commonly known as the laryngeal descent actually evolved in a mosaic way in minimally 2 steps:
(a) a descent of the thyroid cartilage relative to the hyoid, a descent also seen in non-human hominoids,
(b) a descent of the hyoid bone relative to the palate, which is less obvious in non-human hominoids, and which is accentuated by the absence of prognathism in the short & flat human face.
Comparisons with other animals suggest:
(a) the 1st descent might be associated with loud & varied sound production,
(b) the 2d might be part of an adaptation to eating seafoods, such as shellfish, which can be sucked into the mouth, and swallowed without chewing, even underwater.
We argue that the origin of human speech is based on different preadaptations that were present in human ancestors:
(a) sound production adaptations related to the descent of the thyroid cartilage associated with the territorial calls of apes,
(b) transformation of the oral & dentitional anatomy, including the descent of the hyoid, associated with reduced biting & chewing,
(c) diving adaptations, leading to voluntary control of the airway entrances & voluntary breath control ..."
Oral clicks are natural by-products of suction feeding & swallowing without much biting or chewing, not only of seafood (b), but also fruit pulp or other soft & slippery foods.
The consumption of (semi)aquatic foods (rich in brain-specific nutrients such as DHA, as opposed to savanna foods) helps explain Homo's brain enlargement (e.g. S.Cunnane 2005 "Survival of the Fattest: the Key to Human Brain Evolution" World Scient.Publ.Comp. Singapore) and might have promoted the evolution of speech to language (which explains the still huge gap between orangutan & human "speech").
For a recent summary of the littoral theory of human evolution, including speech origins, see my 2013 paper "The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis" (Hum.Evol.28:237-266), google reasearchGate Marc Verhaegen.