Current Affairs

Light pollution disorienting animals that navigate by the night sky

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  • Published
    2nd Aug, 2021
  • Context

    Skyglow forces dung beetles to abandon the Milky Way as their compass.

  • Background

    • The era of electric lighting, which began in the late 19th Century, allowed humanity to extend days into the night with the flick of a switch.
    • As technology has progressed, it has only become simpler and cheaper to light up the world more brightly.
  • Analysis

    How does the Nature’s clock work?

    • The Sun is basically like a clock.
    • The reliable rhythm of night and day gives plants and animals signals for natural cycles of feeding, mating, migrating and navigating.
    • Humans are altering this natural rhythm by flooding the world with artificial light.

    Light Pollution

    • Light pollution, also known as photopollution or luminous pollution, is the excessive, misdirected or invasive use of artificial outdoor lighting.
    • Mismanaged lighting alters the color and contrast of the nighttime sky, eclipses natural starlight, and disrupts circadian rhythms (the 24-hour processes of most organisms), which affects the environment, energy resources, wildlife, humans and astronomy research.
      •  ‘skyglow’ is an omnipresent sheet of light across the night sky in and around cities that can block all but the very brightest stars from view.
  • About the Study

    • In the journal Current Biology, the researchers show that South African dung beetles (Scarabaeus satyrus) are unable to use their star compass under light-polluted skies.
    • Researchers tested how dung beetles responded to two types of artificial light:
      • a single bright beacon
      • the dull glow a nearby city might produce
    • Both kinds disoriented the dung beetles, throwing them off their usual path.
    • When exposed to the bright light, the beetles headed toward that, and when exposed to the ambient light, they went in circles.

    In the study, researchers compared the dung-rolling performance of beetles in a rural part of Limpopo province with that of beetles at the University of Witwatersrand in inner city Johannesburg, both in South Africa.

  • What factors contribute to growing light pollution?

    • Increasing urbanization
    • installation of new streetlights
    • security floodlights
    • outdoor ornamental lighting

    Sky compass

    • Nocturnal ants use landmarks for outbound journeys, but need their sky compass when returning home.
    • Migratory birds have a magnetic compass, with which they check latitude and magnetic North, but use their sky compass to calibrate their magnetic compass to geographic North.
  • Why the findings are concerning?

    • Habitat disturbance: The light that beams from skyscrapers, office blocks, streetlights and homes spills into the habitats of animals.
    • It scatters into the atmosphere, creating a sky glow that can extend around 150 miles(241km) from large towns and cities.
    • Many animals seem to navigate using the stars (birds, seals, and moths), the fading of the night sky could be having similar effects on other species as well.
    • There are over 250,000 birds a day that are getting lost in their migration or light pollution patterns.
    • The impacts of light pollution spill into almost every ecosystem.
      • Artificial light has huge impact on almost every part of insects' behaviour.
        • Light pollution, for example, can changethe foraging behaviour of nocturnal insects, making it harder for them to find food, and for creatures such as fireflies, which rely on bioluminescence to attract a mate, artificial light can confuse males and make it difficult for them to find females.
      • Fish: Artificial light can affect fish by suppressing melatonin, the hormone that controls sleep patterns, setting an internal clock for processes like reproduction and growth.
      • Turtle: It disrupts the nesting behaviour of turtlesand draws newly-hatched marine turtles away from the sea, increasing the risk they will die before they ever reach the water.
      • Bats: Some species of bats associate artificial light with predators, meaning in brightly-lit cities they can be left with "nowhere for them to go.
      • Coral reefs: Even coral reefs are damaged by light pollution.
  • How countries are working towards reducing light pollution?

    • Sloveniapassed a national law to reduce light pollution in 2007, requiring outdoor lighting to be shaded and not exceed certain levels of brightness.
    • Puerto Rico, which has three bioluminescent bays, passed light pollution legislation in 2008.
    • France introduced laws on outdoor lighting in 2019, leading to a 6% decreasein light pollution.
    • Croatiapassed a law restricting lighting levels in 2019.
    • At least 17 US statesand the District of Columbia have some form of light pollution legislation.
  • Conclusion

    Light Pollution is just one additional stress to the whole ecosystem that needs to be taken care of immediately." Cities can put lights on dimmers and install motion sensors or timers to help. Instead of blue and white lights that mimic daytime, amber red lights are a better option.