Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the worldSpecies: Pterodroma baraui
Habitat: Reunion Island in the western Indian Ocean, mating 'neath the pale moonlight
Name an animal that is most active during the full moon, and even those of us untouched by the charms of the Twilight movies might think werewolf.
Our subject today is no mythical beast, however. The Barau's petrel is one of a handful of tropical birds that uses the moon as a kind of alarm clock. During breeding season, the bird travels to mating sites on the aptly named Reunion Island off the shore of Madagascar to meet its mate.
The monogamous birds synchronise their journeys using the full moon as a kind of Bat-Signal to indicate that it's time to mate. "First arrival at the colony is crucial in the mating system of colonial animals like seabirds," writes Patrick Pinet of the University of Réunion, France.
It's not uncommon for birds to take cues from the intensity of sunlight or the length of the day to determine the seasons for migration and mating. Circadian clocks are influenced by melatonin secretions, which reflect the amount and intensity of daylight.
But the Barau's petrel migrates longitudinally – that is, parallel to the equator – so there isn't much difference between the hours of sunrise and sunset in winter and summer.
Still, the slight changes in daylight do affect the petrels. Daily and seasonal changes in melatonin secretion indicate time of day and the time of the year for these birds. But to migrate at the right time to ensure they meet their partners, they need something that varies more reliably.
Pinet and colleagues studied Barau's petrels over two years to see if the animals adjusted their behaviour according to moonlight levels.
During nights with a full moon the birds were significantly more active, spending 80 per cent of their time in flight, instead of resting on the water. Pinet's team also found that arrival dates to the colonies during mating season coincided with the full moon.
Pinet's team was the first to use "bio-loggers" to track the influence of light levels on the behaviour of free-flying birds. These small, lightweight devices were tied to the birds' feet, where they did not interfere with flight. Sensors recorded the amount of time submerged in water and the amount of light taken in, which gave the team a good estimate for the birds' location and activity.
The team speculate that the increase in activity could mean the petrels are foraging for prey that is easier to see and more active itself in the moonlight.