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Light Pollution Can Interfere with the Remarkable Navigational Abilities of Monarchs, Study Says

Biologists from the University of Cincinnati state that nighttime light pollution could intervene with the exceptional navigational abilities of monarchs. Monarchs travel as far as Canada to Mexico and back at the time of their multi-generational migration.

UC assistant professor Patrick Guerra studies the amazing navigation of monarch butterflies. Image Credit: /Lisa Ventre/UC Creative + Brand

Scientists discovered that butterflies roosting at night near artificial illumination like a streetlight or porch can turn out to be confused the next day since the light meddles with their circadian rhythms.

Artificial light has the ability to hinder the molecular processes accountable for the remarkable navigational ability of the butterfly and activate the butterfly to take wing when it must be resting.

We found that even with a single work light that you find at a construction site, monarch butterflies treat that like it’s the sun.

Patrick Guerra, Assistant Professor, University of Cincinnati

The study was reported in the iScience journal.

Having an unpredictable and circuitous movement taking them to and fro across gardens, it might be difficult to envision monarch butterflies sticking to a firm flight plan. However, their migrations take few monarch populations thousands of miles to the same forests in Mexico where they tend to spend the whole winter.

Monarchs are not considered special in their multigenerational migrations, stated co-author and UC master’s graduate Samuel Stratton. He is pursuing a doctorate at the University of Michigan.

Stratton stated, “Multigenerational migration is a common system in insects. It’s a fairly common but less observed phenomenon.”

For instance, the painted lady butterfly takes six generations to travel 9,000 miles (or 14,484 km) from Africa to the Arctic Circle and back. The green darner dragonfly takes around three generations to move from midwestern and northern states to southern states where their grandchildren overwinter.

At present, scientists wish to know if light pollution is hindering this incredible cross-country trek in monarchs.

Stratton stated, “It's an important question given that many migrants fly through urban areas. Getting some ecological data would be really helpful to see what impacts light pollution can have on orientation and migratory outcomes.”

Monarchs depend on the darkness of night to process proteins that are needed for their internal compass. This helps the insects communicate which direction to fly to reach their southern wintering grounds and get back.

The animal keeps track of day and night from this molecular system of production and degradation of proteins.

Patrick Guerra, Assistant Professor, University of Cincinnati

Light pollution could interrupt the normal circadian rhythms and sleep-wake cycles of both wildlife and people. City lights have been observed to interrupt the navigation of animals like baby sea turtles. They mistake them for the glow of the moon on the ocean and move away from the water while they hatch.

Scientists have analyzed the impact of light pollution on birds and other animals that migrate at night.

We wanted to focus on animals that migrate during the day.

Patrick Guerra, Assistant Professor, University of Cincinnati

Millions of monarch butterflies residing in the east of the Rocky Mountains quit their summer breeding grounds in southern Canada and the northern United States. They travel as much as 2,500 miles (or 4,000 km) to overwintering sites present in Mexico.

Monarchs can occupy five generations at the time of this cross-continent trek and back. Along the way, they utilize an internal clock that tells them where to direct themselves in relation to the altering position of the sun in the sky.

However, monarchs that are vulnerable to nighttime light pollution, like a street lamp above their selected roost in a cedar tree, could experience a phase shift, thereby making their body think it is either earlier or later compared to what it really is. The UC scientists discovered that they can throw off their sense of time.

Guerra stated, “It’s like jet lag. Essentially, their sense of time is disturbed.”

Adam Parlin, a UC postdoctoral researcher who is now with SUNY-ESF, headed the study.

UC scientists illustrated this impact by conducting controlled laboratory studies. They simulated and separated the effects of light trespass perturbation on migratory animals that are generally active during the day.

He added, “We found that you’re messing with their day-night cycle. Light pollution can make them think that the day is longer or that the day starts sooner.”

Hence if humans want to be hospitable to monarchs, Guerra said, turning off the light would be of great help for them.

Guerra stated, “It’s something to think about if you’re making a pollinator garden or if you want to be eco-friendly.”

Journal Reference:

Parlin, A. F., et al. (2022) Oriented migratory flight at night: Consequences of nighttime light pollution for monarch butterflies. iScience.


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