Lunar eclipses have a peculiar effect on migratory swifts

(ORDO NEWS) — With the rising of the full moon, the northern black swift (Cypseloides niger borealis) also rises. When this little bird migrates from the Rocky Mountains to the Amazon rainforest, researchers have found that it uses moonlight to recuperate.

During full moon periods, tiny trackers and sensors attached to northern swifts show that they regularly rise to great heights, sometimes as high as 5,000 meters above sea level.

Based on their increased flapping, the researchers suspect that the ascending birds are feasting on aerial insects, which are easier to hunt by moonlight.

On one of the nights during the eight-month migration, during a total lunar eclipse, the birds quickly lost altitude, which indicates the direct influence of moonlight on their flight.

Although previous studies have shown a similar rise and fall of flying insects with the Moon, this is the first time that the lunar cycle has been linked to bird altitude.

“The dynamics of high-altitude flight depending on the different phases of the moon came as a complete surprise to us,” says biologist Anders Hedenström from Lund University in Sweden.

“We found that the black swift does not land even once during its migration, which lasts eight and a half months, so it is always in the air.”

Researchers are still not sure if it is the light of the moon that causes swifts to increase their flight altitude, or if some other factor comes into play. They know that as darkness falls, black swifts descend lower in the sky and lower their activity levels.

There is always the possibility that birds fly higher when the night is lighter to avoid predators rather than to eat, but the authors note that flying at 2,000 meters above sea level on average seems to be “an unnecessarily large margin of safety”, especially on such a long journey where saving energy is key.

On dark nights, for example, on a new moon, swifts flew on average at an altitude of about 700 meters above sea level.

“Therefore, we argue that predator avoidance is an unlikely cause of the periodic shift in swift flight altitude associated with the moon,” the authors conclude.

“The capture of prey, which includes accelerations and flapping flight maneuvers, is likely to increase the level of activity that was recorded by multisensor data loggers.”

The effect of the lunar cycle on animal behavior is known as the “lunar effect” and it affects a wide range of creatures including oysters, corals, zooplankton, sharks, seabirds and lions.

Many of these behaviors are associated with the light of the moon, and some are associated with the ebb and flow of the tides. But others are a complete mystery.

For example, shark attacks seem to increase during the full moon period, but most of them occur in broad daylight, when people usually swim.

There’s still a lot we don’t know about how Earth‘s nearest neighbor affects life on our planet.

Bird migration has been linked to the lunar cycle before, but never to altitude. For example, European nightingales, starting their migration, are guided by the moon.

These birds also migrate twice as actively on moonlit nights when they hunt for insects.

Now, it looks like the northern black swift can do something similar. To the best of our knowledge, this may be a relatively common lunar effect.

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