Azara's owl monkeys move to the rhythm of the moon. On nights when a full moon floods the evening sky with light, Azara's owl monkeys cannot sit still. They are so active that by dawn the next morning, they are worn out. But when the lunar cycle wanes and the moonlight fades, Azara's owl monkeys grow less active at night. On mornings after moonless nights, they are more active during the dawn hours.
The owl monkey genus is unique among anthropoids (monkeys, apes and humans) because it is the only group whose members are nocturnal. Owl monkeys inhabit a range that extends from Central into South America and stretches from Panama to Paraguay.
Among owl monkeys, Azara's owl monkeys stand out, because although they are active during the night, they also exhibit spikes of activity at dawn and dusk.
A research team lead by Eduardo Fernadez-Duque at the University of Pennsylvania conducted a study to find out what was driving the unique activity patterns in Azara's owl monkeys. They fitted 10 Aotus azarai monkeys with special collars that recorded the monkeys' activity at 5 minute intervals for several months. They later recaptured the monkeys and retrieved the collars and the data they contained.
They found that in low and high light conditions--on dark moonless nights or during broad daylight for instance--Azura's owl monkeys were inactive. The monkeys instead favored intermediate light levels such as moonlight nights, and the soft lit hours of dawn and dusk. During those times the monkeys were more active.
Another trend Eduardo Fernadez-Duque and his team discovered was that temperature played a role in influencing how active the monkeys were. During the warm months of September to March monkeys were more active than the were during the cool months of April to August.
Eduardo Fernadez-Duque and his team proposed that the monkey's circadian rhythms relies on daily light-dark cycles. But superimposed over this circadian rhythm is another rhythm, one that responds to the phases of the moon and sways to the ambient temperature.
Refs:
Fernández-Duque, E., de la Iglesia, H., & Erkert, H. (2010). Moonstruck Primates: Owl Monkeys (Aotus) Need Moonlight for Nocturnal Activity in Their Natural Environment PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012572
Photo © University of Pennsylvania.
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