Humans have long marvelled at the night sky above us, inspired by the Moon and the stars to invent stories and myths, travel the oceans and learn more about the Universe in which we live.
At the same time, animals have also been using the stars and other celestial cues to orient themselves.
More astronomical animals
From tiny foraging ants and dung-rolling beetles using moonlight, to birds navigating their migration by the stars, a wide variety of species rely on the night sky to thrive and survive.
Sea turtles
Both the female turtles that lay their eggs on their natal beach and the hatchlings that emerge a few weeks later head towards the brightest horizon to enter the ocean, where the water reflects the light of the Moon – avoiding the darker landward silhouettes.
However, artificial lights from urban developments –known as light pollution – disorient them and they can end up circling the beach in confusion or worse, head towards our roads and buildings – sometimes with fatal consequences.
Moths
It’s well known that many moth species will fly towards a candle, lamp or other light source – a behaviour called positive phototaxis.
It’s been theorised that this is because they are mistaking it for a celestial cue that they would use for orientation.
A recent study using three-dimensional flight data suggests that nocturnal moths turn their back on the brightest light – historically the Moon and the sky – and this would tell them which way was up.
With the introduction of other, human-made sources of illumination, the insects become trapped in a loop, sometimes flying upside down and occasionally causing an insect to crash.
The scientists suggest that the moths are not attracted to artificial lights but trapped by them, similar to being caught in a net.
Bats
While bats are famous for their echolocating skills and are known to use visual and olfactory cues when hunting or navigating, some bats have also been found to use polarised light.
The polarisation patterns from the Sun can still be seen after dusk and bats in research studies were able to use the patterns to orient themselves.
However, scientists are unsure how the bats are actually able to detect the polarisation.
Other studies have examined whether the way bats hunt is impacted by lunar phases, as it’s long been thought that they might have ‘lunar phobia’, where they decrease their activity due to potential predation risk.
However, it seems to vary between different species. One study compared five species and found that one reduced foraging in moonlight, two increased it and two were unaffected.
Another study found that bats changed the habitat where they were hunting.
Indigo buntings
The indigo bunting, so-named for the beautifully vibrant colours of the male bird sporting his breeding plumage, was one of the key species featured in 1960s studies to prove that birds migrating at night used stars to help orient themselves.
One of the main studies involved captive wild birds kept in a planetarium, where the display of the celestial skies could be manipulated by the scientists.
When the display was flipped by 180˚, the birds reoriented themselves to face the right direction to prepare for migration – facing south ready for the autumn migration or north for the spring migration.
European eels
Once hypothesised by the philosopher Aristotle to spontaneously spawn from mud, eels have long been a mysterious animal to humans.
In 1922, it was discovered that they breed in the Sargasso Sea and their larvae gradually drift back towards Europe over a couple of years.
They then become glass eels and return to European rivers to mature.
One study found that in the open ocean the larvae swim more deeply during the full Moon, while other research found that glass eels heading back to the rivers use the Moon’s position to orient themselves at sea and are likely also using a variety of other senses to find their way, including the Earth’s magnetic field and olfactory cues.
Harbour seals
Scientists have discovered that seals can recognise stars inside a modified planetarium.
In an experiment, two harbour seals were placed in a five-metre round pool beneath a dome simulating the Northern Hemisphere’s night sky.
Researchers used a laser pointer to highlight a star, training the seals to swim towards it for a reward.
Later, they changed the dome’s orientation and removed the laser, yet the seals still swam towards the correct star.
This suggests harbour seals naturally recognise star patterns and may use celestial navigation in the wild.
Dung beetles
A study published in 2013 provided evidence of an amazing behaviour exhibited by dung beetles.
Earlier studies had shown that nocturnal dung beetles were able to use light from the Moon to orient themselves.
In this new study, scientists found that even on clear moonless nights the beetles were still rolling their dung in straight lines.
Further experiments conducted in the Johannesburg planetarium, where the night-sky display could be manipulated, showed the beetles continuing to roll their balls in straight lines using starlight but even doing so if only the Milky Way and no other regions of starry sky were shown – the first time this behaviour had been found in any animals.
Bull ants
Bull ants have been known to use the sunlight of evening and morning twilight for navigation. However, some are known to leave the nest in the nighttime and find their way safely back to it. How?
Researchers used a polarisation filter to show that these ants were using moonlight, which is visible to them even on cloudy nights, to follow a course back home.
This is the first time any animal has been shown to use the dim polarisation pattern produced by the Moon for homing and only the second evidence – after the dung beetles – of it being used for orientation in animals.
This article appeared in the May 2025 issue of BBC Sky at Night Magazine
