Moonlight Dictates When Some Birds Fly South

Forget cooling temperatures, the amount of moonlight apparently dictates when some birds fly south in the fall. 

That's according to new research from Lund University in Sweden, which showed the presence or absence of moonlight weighed on the bird's decisions to take flight. The study was published in journal PLOS Biology.

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European nightjars like to hunt by sight

Researchers led by Gabriel Norevik of Lund University looked at European nightjars and how the lunar cycle and moonlight impacted the departure time when the birds began their migration to areas south of the Sahara. The flight typically takes the birds three months to get to the warmer climate.

The researchers studied 39 European nightjars for a year and found the birds searched twice as much for insects to eat when the moon was out compared to when it was dark. The birds started their migration flight roughly ten days after the full moon with the birds all taking off around the same time. 

It would make sense that the European nightjars hunt more when the moonlight is out since they use sight to find insects. They find it easier with the glow of the moon, giving them the energy to take flight. 

"It surprised us that the lunar cycle and the time the birds spent on hunting insects co-vary so well. This, in turn, affects their migration pattern in such a way that they synchronize their flight so that practically all of them fly off at the same time ten days after the full moon", said Gabriel Norevik in a press release highlighting the results of the research.

Migration comes in stages 

The researchers also found the birds tend to take three stages to make it to their final warmer destination. They migrate from Sweden to northern Europe and then to the sites south of the Saraha. At each stage, they follow the same pattern of hunting in a more frantic pace when the moon provides a lot of light. The next stage of the migration starts about ten days after the full moon.  "We will go on to examine that and what effects this type of synchronized migration has on the birds themselves and their surroundings," Norevik said in the release.