Owl monkey and melatonin puzzle

Since 2002, our research muse has been owl monkey (Aotus), a native to Neo-tropical region. Due to their evolutionary choice of nocturnal life, owl monkeys do possess many secrets which diurnal living species like humans still cannot fathom. As of now, nothing is known about the circadian variation of melatonin in owl monkeys. Simply stated, two established facts are, (1) melatonin promotes sleep in diurnal primates including humans. (2) Melatonin levels in the cerebrospinal fluid, serum and plasma of diurnal primates like rhesus monkey, chacma baboon, common marmoset and humans peak during night hours. If this is so, how owl monkeys maintain their night alertness and daytime sleep routine and what role melatonin plays in the circadian zeitgebers of owl monkeys still remains a puzzle to be solved.