In the Scientific American of June 2002, Maggioncalda & Sapolsky describe their research into arrested development of orangutan males - their adolescent stage is usually a few years, but can last longer than a decade, about half their reproductive lives.
They looked at hormonal levels in the urine of captive orangutans, despite the fact that blood would be the ideal source of information, “for practical and ethical reasons”.
Which brings up the question - can orangutans be trained to donate blood in exchange for treats? I’m imagining some kind of wall with a hole in it…the orangutan sticks his arm into the hole, its arm is immobilized, the keeper takes the blood sample, releases the arm and provides the treat. Certainly the higher primates can be trained to do all sorts of things - Washoe and Ameslan, for instance - so this wouldn’t seem to strain credulity. Or does it?
