Many animals have evolved impressive abilities to navigate vast distances, even across entire oceans, to find their way back home or to migration sites. While smell, landmarks, and magnetic fields provide navigational aids, some animals have acquired the remarkable ability to use the stars for orientation and navigation.
Which animals use the stars for navigation?
The most well-known animal navigators of the night sky are birds. Many migratory bird species use celestial cues from stars, the sun, and even polarized light patterns to determine their direction. Other animals known to orient with the stars include sea turtles, seals, some butterflies and moths, and dung beetles.
Birds
Many migratory bird species are capable of using the stars for orientation during their biannual migrations. These include:
- Indigo buntings
- Emlen’s sparrow
- Northern wheatears
- Savannah sparrows
- White-throated sparrows
- Warblers
- Bobolinks
- European starlings
- Geese
- Ducks
- Sandhill cranes
- Pigeons
- Owls
- Swallows
Experiments on migratory birds have shown they can orient themselves using just the stars, even on clear moonless nights. Their ability seems to be innate rather than learned. Even birds raised in captivity with no exposure to the night sky can orient properly during migration using stellar cues alone.
Sea Turtles
Young sea turtles use visual cues to help guide them from their nesting beaches across entire oceans to feeding grounds they’ve never visited before. Experiments indicate celestial information from the stars provides orientation for young green and loggerhead turtles during their first migration. Their navigational abilities appear sensitive to light pollution, which can disorient hatchlings.
Seals
Seals have demonstrated the capacity to orient themselves using the stars while offshore. In experiments, seals trained to swim in specific compass directions could orient properly at night by the stars alone, indicating they can use celestial cues for navigation.
Insects
A few insects are also known to orient with the stars:
- Dung beetles use the celestial polarization pattern to roll their dung balls along straight paths.
- Some moths and butterflies likely use skylight cues for long-distance migration.
How do animals use the stars to navigate?
Animals that orient with the stars are using celestial cues as a guide to determine their bearing. By calculating their position from the stars, they can travel in their intended direction, even across vast unfamiliar landscapes or seas. Some key ways animals use stellar information:
Determining latitude
As stars revolve around the pole star in fixed patterns, animals can estimate their latitude by reading the position of circumpolar stars. For example, birds prepare for migration by using star patterns to calibrate their internal magnetic compass to the proper latitude.
Discerning compass direction
The predictable daily rotation of stars around the pole provides animals an accurate reference for direction. Birds and sea turtles can set their course by locating key stars or constellations.
Maintaining orientation overnight
On long migrations, animals may use stellar cues at night to stay on course when other cues like the sun are unavailable. This prevents drifting off path while resting overnight.
Recalibrating when other cues are lacking
If weather obscures other navigational aids like the sun or magnetic fields, a view of the stars can help recalibrate an animal’s sense of direction to stay on track.
What star patterns do they follow?
While the exact stellar cues animals rely on for navigation vary across species, here are some key star patterns known to provide orientation information:
Polaris – The North Star
As the northern celestial pole, Polaris marks north and alignment with the Earth’s axis for animals in the Northern Hemisphere. Birds often locate it to determine latitude.
Cassiopeia
The W-shaped Cassiopeia constellation rotates around the pole star opposite Ursa Major. Some birds use it as a north directional reference point.
Ursa Major – The Big Dipper
Ursa Major circles Polaris through the night. Its pointer stars can point toward north. Some birds use the Big Dipper for navigation.
Orion
Orion is one of the brightest and most recognizable constellations. Some birds use its orientation to estimate compass direction.
Scorpius and Sagittarius
These constellations’ positions in the southern sky assist birds migrating between the Southern Hemisphere and the equator.
How does light pollution affect animals that navigate by the stars?
Increasing light pollution from urban expansion poses a threat to animals that orient themselves using celestial information from the stars, moon, and polarization patterns:
- Bright artificial light can obscure the visibility of key stars used for navigation.
- Skyglow can disrupt an animal’s perception of celestial patterns.
- Glare from artificial lights can overwhelm an animal’s visual orientation system.
- Disrupted polarized light patterns can confuse navigation senses.
Impacts linked to light pollution’s interference with stellar navigation include:
- Young turtles disoriented by coastal lights leading to death.
- Birds circling in confusion around illuminated buildings.
- Altered migration routes in birds.
- Change in some bird species’ ability to calibrate magnetic compass.
- Disrupted foraging and reproduction behaviors.
Targeted efforts to reduce light pollution during key migration and hatching times could help mitigate these impacts.
How do animals perceive the night sky differently than humans?
While humans see a beautiful but abstract starry sky, many animals have evolved unique ways of perceiving key celestial information useful for navigation:
Increased light sensitivity
Animals like owls and seals have higher rod photoreceptor density allowing better night vision in low light compared to humans.
Ultraviolet vision
Some birds see into the ultraviolet spectrum, allowing them to discern patterns humans can’t see with visible light alone.
Visual magnetoreception
Birds may visually sense magnetic field information affecting light entering the eye to determine compass direction.
Polarization vision
Some species like dung beetles analyze polarization patterns in skylight providing navigational information even on moonless nights.
Innate stellar map
Birds and sea turtles possess an innate capacity to orient themselves using celestial cues, even without prior experience.
How does weather affect animals’ use of stars for navigation?
While stars can provide reliable long-term navigational information, weather conditions can impact animals’ ability to utilize stellar cues:
- Thick cloud cover blocks view of the stars.
- Precipitation like rain or snow degrades visibility.
- Fog scatters light, obscuring celestial patterns.
- Bright moonlight can diminish star visibility.
When stellar information is unavailable, animals may switch to using backup cues like the sun or magnetic fields. However, thick or long-lasting cloud cover can deprive animals of any celestial references, sometimes leading to navigational errors.
Impact of weather on migration
| Weather Condition | Impact on Bird Migration |
|---|---|
| Clear weather | Allows optimal use of stars, stable migration patterns |
| Light cloud cover | May slightly disrupt stellar visibility but most birds compensate successfully |
| Overcast weather | Blocks stars, forcing reliance on backup cues like sun or magnetic fields |
| Severe storms | Can disorient migration by obscuring all celestial cues for long periods |
| Unseasonable weather | Alters expected environmental cues, increasing navigational challenges |
Conclusion
The remarkable ability of birds, sea turtles, seals, insects, and other animals to navigate using the stars has evolved over millennia as a critical adaptation for migration and other long-distance movement. By discerning celestial information humans can barely perceive, animals can achieve amazing navigational feats spanning continents and oceans. However, increasing light pollution threatens to obscure the stellar compasses animals rely on, requiring greater efforts to understand and protect these unique talents of the natural world.
