European nightjars are more active during moonlit nights, GPS tracking data reveals.
Scientists studying the nocturnal birds have found their daily foraging movements “more than doubled” during bright nights.
The findings from the experimental study, published in the open-access journal PLOS Biology, also show that these birds then tend to migrate shortly after the full moon.
The researchers from Lund University in Sweden say their work could improve the understanding of how migratory animals time their move.
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European nightjars have acutely sensitive eyesight and their eyes contain a reflective layer behind the retina that gives them good night vision.
Known for their distinctive ‘churring’ call at dusk, these birds can be spotted in large numbers in heathlands, moorlands and open woodlands during late spring and summer in southern England.
Smaller populations can also be found in parts of Wales, northern England and south-west Scotland.
Nightjars travel between north Europe and southern Africa, spending the winter in the southern hemisphere before returning to Europe during late spring to breed.
Gabriel Norevik, a postdoctoral fellow at Lund University, told the PA news agency: “The night-time ecology of nightjars and the many other nocturnally active animals still is an under-represented research field, we still know relatively little about the causes and consequences of their decisions.”
The researchers used GPS tracking data to record the movements of 39 nightjars.
They also used tags specially designed to analyse the birds’ flight patterns by measuring their wingbeat – the motions of wings during flying.
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The scientists were able to distinguish intermittent flight activity – associated with foraging when the birds hunt for flying insects – from migratory flight, which shows more intensive flight activity.
The daily foraging activity of the nightjars more than doubled during moonlit nights, the researchers said.
This increased activity resulted in a clear cycle in the intensity of migratory movements – with the birds migrating simultaneously about 10 days after the full moon, they added.
Reader Q&A: Do birds fart?
Asked by Lorely Maskell
Birds have an anus, and so technically could fart, but to date there’s been no official evidence that they do. One theory is that they don’t need to fart like humans and other mammals because they have a faster rate of digestion – their food simply doesn’t spend long enough in their short gastrointestinal tracts to ferment and form gas.
Another theory is that birds’ guts don’t contain the same gas-forming bacteria as mammals. It’s also possible that ornithologists have missed bird farts because they leak out passively rather than in one eruption, or birds could be burping to release unwanted gas instead.
Dr Norevik told PA: “We wanted to understand how the bird’s nocturnal lifestyle could affect the seasonal migration, hypothesising that their dependence of dim light conditions to find their food would constrain their ability to prepare for the flights.
“We show that nightjars become predisposed to move after periods of moonlit nights.
“Worldwide, animals migrate by the billions every year and our findings may improve our understanding of how and when many of them time their movements.”