In addition to planting milkweed in the garden, those interested in helping monarch butterflies may want to turn off the porch light.
University of Cincinnati biologists say nighttime light pollution can interfere with the remarkable navigational abilities of monarch butterflies, which travel as far as Canada to Mexico and back on their multigenerational migration.
Researchers have found that butterflies that roost near artificial lighting like porches or lampposts at night can become disoriented the next day because the light interferes with their circadian rhythms. Artificial light can interfere with the molecular processes responsible for the butterfly’s remarkable ability to navigate and cause the butterfly to take flight when it should be resting.
“We found that even with a single work light that you find on a construction site, monarch butterflies treat it like it’s the sun,” said UC assistant professor Patrick Guerra.
The study was published in the journal iScience.
With their erratic, devious movements moving them back and forth through your garden, it can be hard to imagine monarch butterflies sticking to a rigid flight plan. But their migrations take some populations of monarchs thousands of miles to the same forests in Mexico where they spend the winter.
Now the researchers want to know if light pollution is hindering this incredible trek across the country.
“This is an important question given that many migrants pass through urban areas,” said co-author and UC master’s graduate Samuel Stratton. “Getting ecological data would be really useful to see what impacts light pollution can have on orientation and migration outcomes.”
Monarchs rely on the darkness of night to process proteins essential to their internal compass. These help insects tell which direction to fly to reach their southern wintering grounds and return.
“The animal keeps track of day and night from this molecular system of protein production and breakdown,” Guerra said.
Light pollution can disrupt normal circadian rhythms and sleep-wake cycles in wildlife and humans. City lights have been shown to disrupt the navigation of animals like baby sea turtles, which mistake them for the moonlight on the ocean and move away from the water when they hatch.
Researchers looked at the effects of light pollution on birds and other animals that migrate at night.
“We wanted to focus on animals that migrate during the day,” Guerra said.
Millions of monarch butterflies living east of the Rocky Mountains leave their summer breeding grounds in southern Canada and the northern United States, traveling up to 2,500 miles (or 4,000 kilometers) to sites of wintering in Mexico.
Monarchs can take up to five generations on this round-trip trek across the continent. Along the way, they use an internal clock that tells them where to orient themselves based on the changing position of the sun in the sky.
But monarch butterflies exposed to nighttime light pollution, like a street lamp above their chosen perch in a cedar tree, can experience a phase shift, tricking their bodies into thinking it’s earlier or later than it is. actually is. This can disrupt their sense of time, UC researchers have found.
“It’s like jet lag,” Guerra said. “Essentially, their sense of time is disrupted.”
UC postdoctoral researcher Adam Parlin, now with SUNY-ESF, led the study.
UC researchers demonstrated this effect by conducting controlled laboratory studies. They simulated and isolated the effects of light intrusion disturbance on migratory animals normally active during the day.
“We found that you’re disturbing their day-night cycle. Light pollution can make them think the day is longer or the day is starting earlier,” he said.
So if you want to be hospitable to monarchs, Guerra said, maybe don’t keep the lights on for them.
“It’s something to think about if you’re making a pollinator garden or want to be eco-friendly,” Guerra said.