Low melatonin is related to high nocturnal vocal output and plasticity in a free-living songbird
Kim G. Mortega • Sarah Kiefer • Michaela Hau • Silke Kipper
The pineal hormone melatonin plays an important role in the regulation of daily rhythms in vertebrates. Typically, melatonin is secreted in a diel fashion, resulting in elevated circulating concentrations at night and low concentrations during the day. In some diurnal avian species, nocturnal activity is associated with reduced concentrations of melatonin at night, for example during periods of night-time restlessness during the migratory season. Here, we tested whether melatonin concentrations are associated with nocturnal activity, as well as with sexually selected song characteristics during the courtship season in nocturnally singing nightingales, Luscinia megarhynchos. Nocturnal plasma concentrations of melatonin levels of displaying nightingales were among the lowest ever found in songbirds and did not differ from diurnal levels. Nocturnal melatonin was positively correlated with nocturnal singing activity. Males with low nocturnal melatonin were more likely to continue singing. These findings suggest a previously unknown role of melatonin in the plasticity of nocturnal singing during the mating season.
photo credit: Josef Vorholt