Minnesota’s lakes are running low on oxygen

This story originally featured on Nexus Media News, a nonprofit climate change news service.

On a sweltering morning in July of 2021, thousands of dead fish washed onto the northeastern shores of Pokegama Lake, 60 miles north of Minneapolis. 

Deb Vermeersch, an official with the Minnesota Department of Natural Resources, was called in to investigate. 

When she arrived, she saw a quarter-mile stretch of sand covered with the rotting carcass of walleye and Northern pike, which thrive in deep, cool waters, as well as crappies, sunfish and suckers—all warm water dwellers. “They were already pretty decomposed because of the warm water,” Vermeersch recalls. 

Because so many different types of fish had died, Vermeersch and her colleagues knew it wasn’t a species-specific parasite, a common cause of fish kills. They zeroed in on the culprit: dangerously low oxygen levels.

Oxygen is disappearing in freshwater lakes at a rate nine times that of oceans due to a combination of pollution and warming waters, according to a study published in Nature earlier this year. Lakes like Pokegama are warming earlier in the spring and staying warm into autumn, fueling algae blooms, which thrive in warm waters, and threaten native fish.

Minnesota, with its 14,380 lakes and temperatures that have risen faster than the national average, is a unique laboratory for studying how climate change is affecting temperate-zone lakes around the world. The state sits at the intersection of four biomes––two distinct prairie ecosystems and two ecologically different forest systems. This means scientists here are able to study how lakes in different ecosystems fare on a warming planet, and look for ways to stave off the worst effects of climate change. 

“If you start losing oxygen, you start losing species.

“What’s going on at the surface is that warmer water holds less oxygen than cool water,” says Lesley Knoll, a University of Minnesota limnologist and one of the authors of the Nature report. She says that longer, hotter summers are interfering with two key processes that have historically kept lakes’ oxygen levels in check: mixing and stratification. In temperate climates, water at the surface of lakes mixes with deep waters in the spring and the fall, when both layers are similar in temperature. As the surface water warms during the summer, the water forms distinct layers based on temperature––cool water at the bottom, warm at the top. This is known as stratification. In the fall, when the surface waters cool again, the water mixes for a second time, replenishing oxygen in deeper waters. But as climate change makes surface water warmer, and keeps it warmer for longer, that mixing doesn’t happen when it should.

“As you have that stronger stratification, the water in the deep part of the lake is cut off from the oxygen at the top part of the lake. If you start losing oxygen, you start losing species,” says Kevin Rose, a biologist at Rensselaer Polytechnic Institute in New York and a coauthor of the Nature study.

Knoll, Rose and a team of 43 other researchers studied 400 temperate lakes from around the world. They found that, on average, surface waters warmed by 7 degrees Fahrenheit and have lost roughly 5 percent of oxygen since 1980; deep waters, which haven’t warmed much, have still lost an average of almost 20 percent of their oxygen. (Thanks to the state’s long-held lake monitoring programs, almost a quarter the lakes in the study were in Minnesota.)

Warming lakes emit methane

Fish kills aren’t the only reason scientists are concerned about lakes losing oxygen. In extreme cases, when deep waters go completely void of oxygen, something else happens: Methane-emitting bacteria begin to thrive.

“As lakes warm, they will produce more methane and most of that has to do with stratification,” says James Cotner, a limnologist at the University of Minnesota.

Lakes normally emit carbon dioxide as a natural part of breaking down the trees, plants and animals that decay in them, but plants in and around fresh water also absorb it, making healthy lakes carbon sinks. 

Lakes have historically emitted methane, too––about 10 to 20 percent of the world’s emissions––but the prospect of them releasing more of the greenhouse gas has Cotner and his colleagues alarmed. Methane is about 25 times more potent than CO2 when it comes to trapping heat in Earth’s atmosphere.

Cotner is leading a team of researchers who are studying what conditions allow methane-emitting bacteria to prosper in lakes and how conservationists can respond. 

“The key questions are understanding how much and when carbon dioxide and methane are emitted from lakes, and what are the key variables that can tell how much will be emitted. Certainly, oxygen is a big part of that, but stratification and warming also plays a role,” says Cotner. 

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Pollution plays a big role

It’s not just longer, hotter summers that are causing lakes to lose their oxygen. Polluted agricultural runoff (pesticides and fertilizers) and logging have long plagued Minnesota’s lakes. It’s a problem that’s getting worse worldwide as climate change pushes agriculture further away from the equator and into new territory, says Heather Baird, an official with Minnesota’s Department of Natural Resources.

In northern Minnesota, potatoes now grow where pine forests have thrived for years. Phosphorus, a common fertilizer, now runs off from the soil into the region’s lakes, Baird says. Though small amounts of phosphorus occur naturally in lake ecosystems, too much of it feeds harmful algae blooms. 

Those blooms, which thrive in warm, nutrient-rich water, set off a chain of events that remove oxygen from deep lake waters.

“When phosphorus builds in lakes and creates algae blooms, those blooms eventually die. As they do, they sink. Deeper down, bacteria break down the algae, using up the remaining oxygen at those lower depths,” said Baird.

A quarter of Minnesota lakes now have phosphorus levels that are so high that the state advises against swimming, fishing or boating in them. Fueled by these nutrients, algae blooms take over, covering the lake in sometimes toxic residue that thrives in warm, nutrient-rich water, as was the case in Pokegama Lake earlier this year. The protists choke out aquatic life, especially fish that thrive in cold, deep waters. This is all exacerbated by warming air temperatures. 

The 75 percent rule

Researchers and conservationists in Minnesota are now studying the best ways to protect temperate-climate lakes from the worst effects of climate change. They have found that preserving 75 percent of deep-water lakes’ watersheds appear to keep fish stocks healthy. 

“Having a forested watershed helps keep better water quality by filtering out nutrients, which in turn can buffer against the impacts of climate change, to a point,” Knoll said. However, she added, as temperatures continue to rise, “that 75 percent may not be high enough anymore.” 

Knoll and state conservationists are focusing their research and efforts on deep, cool lakes that have a better chance of staying oxygenated than warmer, shallower lakes, like Pokegama.

July 2021, when the Pokegama Lake fish kill occurred, was the hottest month ever recorded on Earth. Parts of Minnesota were also experiencing the worst drought in 40 years, a trend some climatologists expect to persist in future summers. 

Vermeersch, the Minnesota fisheries supervisor, said it’s unclear what this will mean for the future of lakes like Pokegama. “Hopefully it’s not going to be a linear thing,” she said, adding that fish kills are “probably going to happen more often,” depending on a combination of factors. “When you get lakes like Pokegama that are shallow and already impaired, I think we are going to see more and more conditions like this.”

Correction (December 23, 2021): The story previously identified the wrong Pokegama Lake in Minnesota. The one that experienced the fish kill in July is 60 miles away from Minneapolis, not 140 miles away.

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How big did ancient millipedes get? Bigger than you’d like.

A fossil found in sandstone near the England-Scotland border contains the largest millipede ever found—and the discovery was completely by accident. 

In January 2018, Neil Davies, an Earth scientist at the University of Cambridge, had taken a group of PhD students on a “social trip” to Northumberland, England, where he had previously gone on holiday. The group noticed some rocks had crashed onto the beach where they were walking. One of those chunks happened to contain a paleontological surprise. 

“The way the boulder had fallen, it had cracked open and perfectly exposed the fossil, which one of our former PhD students happened to spot when walking by,” Davies said in a statement. “It was a complete fluke of a discovery.” 

Davies and his colleagues were at first unsure about what they had found. In May 2018, they extracted the fossil and brought it back to Cambridge for analysis. The specimen is just the third known example of an Arthropleura, a genus of giant millipede that roamed the Earth during the Carboniferous Period, between 359 million and 299 million years ago. But that’s not all: This Arthropleura fossil is also the oldest ever found, dating back to 326 million years ago, as well as the largest. It measures a whopping 30 inches by 14 inches. 

That suggests a pretty impressive beast. The millipede itself was likely around 8.5 feet long and nearly two feet wide, and probably weighed about 110 pounds. The team’s results were published in the Journal of the Geological Society.

[Related: This eyeless millipede shattered the record for most legs]

“Finding these giant millipede fossils is rare, because once they died, their bodies tend to disarticulate,” Davies told BBC. This particular specimen is likely just part of a molted exoskeleton, rather than a piece of a millipede’s corpse. Such a sparse fossil record means that these bugs largely remain a mystery. To this day, “we have not yet found a fossilised [millipede] head,” Davies added, “so it’s difficult to know everything about them.”

For example, researchers are unsure how many legs these millipedes had. Current best guesses are either 32 or 64—a paltry set compared to the maximum 1,300 legs recently found on some living millipedes. Scientists also don’t know what these giant bugs ate to sustain their lumbering bodies, though they seem to have thrived due to an abundance of resources and little competition. But later, in the Permian Period, they went extinct—either because of a changing climate or due to new reptile species outcompeting them for food. To uncover the mysteries still lurking in giant millipedes’ history, researchers will need more examples of them to fill out the fossil record.

The area of Northumberland where the fossil was found is mostly sandstone, which “is normally not brilliant for preserving fossils,” Davies told NPR. So “the fact that this has been preserved is, on the one hand, surprising. But it just suggests that actually there might be a lot more and similar things in places where people haven’t really looked for fossils before.”

The fossil will go on public display at Cambridge’s Sedgwick Museum in the New Year.


Does South Africa still need private rhino breeders to fight poaching?

Ed Stoddard is a Johannesburg-based journalist with a focus on resource industries, wildlife, economics, and the environment in Africa. A Reuters correspondent for 24 years, he is now a regular contributor to the South African news site The Daily Maverick.

This story originally featured on Undark.

Three hours outside Johannesburg, the gravel road to John Hume’s home slices through grasslands tinged a parched amber hue as the winter dry season fades. The former hotel mogul owns the world’s largest privately held rhino population: 2,000 southern white rhinoceroses, roaming 21,000 acres of former crop and cattle lands. A 60-mile long electrified fence rings the property. Its two-fold role is to keep the pachyderms in and poachers out.

Hume has not lost a rhino to poachers in almost five years, thanks to formidable security. Over the past decade though, state-run parks have been overwhelmed by poachers, who can sell a single rhino horn for six-figure sums. As those wild populations decline, research suggests nearly half of South Africa’s estimated 12,300 white rhinos are now in private hands. With the trend of private breeding growing rapidly, some experts say this number may even have already surpassed 50 percent.

But the fate of Hume’s rhinos—and South Africa’s unusual game privatization experiment—hang in the balance. In December 2020, a government panel recommended phasing out intensive and captive rhino breeding in the country, as part of a broader set of policies for wildlife conservation. According to the panel and a subsequent government policy paper, captive breeding operations like the one owned by Hume are potentially harming the species’ future.

In an email to Undark, the panel’s chair, Pamela Yako, expressed two concerns about intensive breeding and management: “that this, firstly, compromises the genetics of the population and secondly compromises their ability to independently survive in the wild.”

While Yako and her colleagues acknowledge the role of private reserves in helping to build up rhino populations, they conclude it’s time to move the more intensively managed private populations back into wilder habitats.

The panel’s report has been accepted by the South African cabinet, signaling top-level political support. After a public comment period, the Department of Forestry, Fisheries, and the Environment will refine the policy, then draft a white paper to send to Parliament.

But the prospect of losing their herds has alarmed many private rhino owners and conservationists, who say the policy will make southern white rhinos more vulnerable to poaching. “We have rhino in well-protected zones,” says Pelham Jones, chairman of the Private Rhino Owners Association, or PROA. Now, he adds, “the government is recommending that these captive breeding operations, which have proven to be highly, highly successful, and are achieving the best breeding outcome one could hope for, are to be shut down.” The group is considering all options, including a legal challenge that would potentially ensnare the process in years of legal wrangling.

At stake here are questions about how best to preserve a threatened species. The politics are fraught as well, and charged by South Africa’s racial tensions: Proponents of the new policy point out that the country’s Black majority has often been excluded from the benefits of rebounding game populations. By PROA’s own estimates, there are between 150 and 180 private rhino owners in South Africa; nearly all of them are White.

None of them has an operation as large as Hume’s, whose herd may account for up to 13 percent of the global population of white rhinos. His ranch also appears to be a prime target of the new legislation. In her email, Yako expressed concerns about “a single operation that has a large number of rhino under intensive management and breeding”—seemingly a reference to Hume, although Eleanor Momberg, a spokesperson for the Department of Forestry, Fisheries and the Environment, wrote in an email to Undark that Yako and other panelists were no longer available for further comment because their contracts had expired.

The new policy could eventually undermine the legal basis for Hume’s breeding project, leaving the herd in limbo. It’s unclear who would take over Hume’s herd—and how a South African state balancing intense fiscal pressures with massive social needs would pay for a mass rhino relocation.

Sitting in his modest home office, which is adorned with rhino pictures and carvings, Hume maintains he is adding to an endangered species’ numbers. “Surely that’s what we all want,” he tells Undark. “Show me the good grazing, and assure me that you can keep the bullets away, and I will show you my rhinos thriving.”


Africa is home to two of the five surviving rhinoceros species: the larger white rhino, a grass grazer, and the smaller black rhino, which browses on trees and bushes. In the late 19th century, European settlers killed thousands of the animals. Every southern white rhino today is descended from a single population in South Africa’s KwaZulu-Natal province. In the 1890s, the animals reached their low point, numbering just a few dozen.

From this bastion—now called the Hluhluwe-Imfolozi Park—the population rebounded. By the 1960s, flush with rhinos, a government organization called the Natal Parks Board began selling and donating animals to other African reserves, and to zoos around the world. In 1986, Natal Parks Board started selling to private operations, too. Five years later, the South African government passed the Game Theft Act, which allows people to own rhinos and other game on their property, provided it has been enclosed with fencing.

The law has critics. In a 2015 dissertation, scholar Dhoya Snijders described the act as “one of the largest and most unnoticed transfers of common goods to private landowners in the country’s history.”

Thanks to the new legislation, game ranchers began to rapidly accumulate rhinos to breed and trade for profit, to draw ecotourists, and to stage expensive hunts. Nowadays, most owners also slice off the animals’ horns and store them, in the event that a now 44-year-old global moratorium on the rhino horn trade is lifted. These owners argue that trading rhino horn may help regulate its illicit traffic and would provide substantial revenue to cover the large costs associated with managing and conservation of the species, said Jones. Comprised of keratin—the substance in human fingernails—rhino horn can grow back after it is trimmed, an operation that entails tranquilizing the animal. De-horning is also aimed at thwarting poachers by removing their ultimate target.

By 2010, there were 18,800 white rhinos in South Africa, according to estimates from the International Union for Conservation of Nature, of which at least 5,500 were privately owned.

But as demand for rhino horn grew in newly affluent Asian economies such as Vietnam—where consumers prize its alleged medicinal properties—poaching surged. A record 1,215 rhinos were poached in South Africa in 2014.

Although numbers have dropped since then, poachers still take hundreds of animals per year. The activity has centered on Kruger National Park, South Africa’s flagship wildlife reserve. The park is vast—roughly the size of New Jersey—making it difficult for the cash-strapped government to police. And entrenched poverty in neighboring communities has pushed some people toward poaching.

Today, as state losses mount, poachers are increasingly targeting private reserves. Government data shows 15 percent of rhinos poached in 2019 were on private land. In the first six months of 2021, that spiked to 30 percent. Owners who can afford it invest heavily in security. Meanwhile, many small-scale rhino ranchers have sold out because of costs.

At least so far, the scale of Hume’s operation—and his deep pockets—have fended off poachers. At Hume’s “Ops Center,” 10 TV screens line one wall. Radars and thermal cameras monitor the property, covering the rhinos’ range and the public roads that cut past the ranch. The flat, grassy terrain is ideal for the motion-detecting radars, which cannot penetrate solid objects such trees or buildings. If an intruder gets over the electrified fence, concealed speakers blare warnings while a team rushes to intercept.

“We are always ready, and we can fly a chopper to the scene quickly if we need to,” says Brandon Jones, a helicopter pilot and Hume’s head of security, with a handgun holstered to his hip. The team’s arsenal includes assault rifles; the poachers are also heavily armed. Hume, who refers to the team as his “private army,” said security costs him $2 million per year.

Although numbers have dropped since 2015, poachers still take hundreds of animals per year. The activity has centered on Kruger National Park, South Africa’s flagship wildlife reserve.

The investment seems to be working. While poachers killed 32 of Hume’s rhinos between 2007 and 2017, he says he has not lost an animal since. More of his rhinos have been killed by lighting strikes.

According to Hume, the operation has accumulated nearly 9 tons of rhino horn, worth a nine-figure sum on the black market. But, he said, his passion for rhinos was driven by the species’ plight in the cross-hairs of poachers, not potential profits. “I always liked breeding,” he says. “I became aware in the early ‘90s of the slaughter of rhino elsewhere in Africa. They were being slaughtered to extinction.” Around that time, he purchased his first 10 animals.

Today, driving around the property, it’s possible to see clumps of rhinos amid the windswept landscape of long wild grass, punctuated by the occasional tree. Other times, there are no signs of the big critters at all, beyond their telltale scat in the soil.


Inside this gated fortress, the number of rhinos on Hume’s ranch has swelled: Between 2008, when he started breeding at his current ranch, and September 2021, Hume’s rhinos had given birth to some 1,690 calves. But whether that growth is an unmitigated good for rhino conservation, or a liability for the future of the species, remains contested.

Yako and other critics of captive breeding have raised concerns that the closely managed life on the ranch could give rise to domestication, a fate that historically has not occurred in any large African mammal, or render the rhino unsuitable for rewilding.

Hume’s rhinos are divided into breeding areas surrounded by electric fencing averaging 1,200 acres. The animals roam, graze, and mate freely in their allotted spaces. But they are intensely monitored, and each enclosure or camp has a ranger who does a daily headcount, often on horseback. Still, Michelle Otto, Hume’s resident and full-time veterinarian, said the animals are far from domesticated. “We are only on our second generation now,” she said, as she prepared medicine for an old cow rhino with hip problems. “I’ve been chased into a tree by a white rhino here because I went in on foot, and one didn’t take a liking to me, and she stormed me.”

Otto said the animals can be habituated to certain vehicles—but, she noted, even wild Kruger rhinos are now accustomed to cars. The ranch does supplemental feeding, mostly in the dry winter months, which Otto said was at most 40 percent of the rhinos’ daily intake. “The rest they take off the veld,” she said.

Some of Hume’s rhinos have already been successfully reintroduced into the wild. Hume sold his last 16 black rhinos—famed for their ornery temperament—to the small kingdom of Eswatini, which borders South Africa. “This group of rhinos has been suitable for introduction, save for one young male which was hand-raised,” wrote Mick Reilly, conservation and security executive with Eswatini’s parks, in an email.

“Hume’s white rhinos as a whole would be suitable for re-introduction into the wild,” added Reilly, who has visited the ranch.

Tranquilized white rhino bull getting dehorned in South Africa
A tranquilized bull rhino gets a trimming at John Hume’s ranch in South Africa on August 5, 2021. Most owners slice off the animals’ horns, which will regrow, and store them in case the moratorium on the rhino horn trade is lifted. De-horning also thwarts poachers by removing their ultimate target. Ed Stoddard/Undark

Yako and others have also expressed concerns about the genetic diversity of rhinos in captive breeding populations. Even in the wild, rhino genetics pose serious issues: A century ago, when population numbers were so low, the bottleneck reduced the genetic variability of the species. According to Petra Kretzschmar, a biologist and rhino expert at the Leibniz Institute for Zoo and Wildlife Research in Germany, this state of affairs made the species vulnerable to disease and fertility problems.

Compounding the issue, rhinos tend to mate with their relatives. “Inbreeding is unfortunately a big threat to the white rhino population,” Kretzschmar wrote in an email. “It is therefore very important to prevent rhinos from inbreeding.”

In a 2020 study of rhino breeding patterns on a large private ranch in South Africa’s northern Limpopo province, Kretzschmar and several colleagues found that white rhinos are not choosy about mating with kin. The study, published in the journal Evolutionary Applications, found “no sign of inbreeding avoidance: Females tended to mate more frequently with closely related males.”

The researchers recommended rotating breeding bulls every six years—the time it takes a female to reach sexual maturity—between reserves.

Kretzschmar, who has visited Hume’s ranch, says policies there do effectively address the issue. Otto keeps detailed records in a stud book to prevent inbreeding. Compared to the private reserve where her study was conducted, Kretzschmar says in a phone interview, Otto “has the benefit that the rhinos can be monitored much better,” as they are put into a smaller spaces that can be more readily observed.

“So her records are much more accurate, which results in the fact that she knows exactly who has fathered whom and can immediately move an animal to a different camp to prevent inbreeding,” says Kretzschmar.

In the paper, Kretzschmar—who also does paid consulting for a private game ranch—and her co-authors said South Africa’s private reserves may be the last refuge for the species.

Still, Hume’s approach has critics.

“In John Hume’s case, there is control over the breeding,” says Dave Balfour, an ecologist and member of the IUCN African Rhino Specialist Group who contributed to the government report arguing for reimagining rhino conservation in the region. He says these breeding strategies “are not anywhere near the gold standard.”

“A natural rhino population has 50/50 male/female” Balfour says, adding that Hume’s project had somewhere between 50 cows to three or four bulls. “That is not a natural mating selection system.” (In a WhatsApp message, Otto defended the ranch’s arrangement. “We are a breeding operation, therefore we are skewed towards having higher female densities in a set location than in the wild,” she wrote, adding that females are permitted to choose among two or three bulls.)

Other critics have concerns about the stockpiling of rhino horn, detecting a profit motive beneath a facade of conservation. “Are you trying to mask an economic incentive behind a conservation philosophy?” asks Neil Greenwood, the Southern African director for the International Fund for Animal Welfare, an NGO. “I don’t think that the captive breeding is necessarily the most effective way to protect those animals.”


At issue are larger questions about the future of wildlife in South Africa, where populations of large, charismatic animals have rebounded. Many are in private hands: Today, according to the government report, there are 9,000 private game ranches in South Africa, comprising around 50 million acres.

The growth of private game reserves has raised some concerns about equity. South Africa is the most unequal society in the world, according to the World Bank, and land ownership patterns remain skewed in favor of the White minority.

According to the government policy paper, many communities with historical ties to wildlife lands have been walled out of the present conservation arrangement. “The forceful removal of people from the land led to the current South African ‘Wildlife Model,’ the report says, “where the largest percentage of wildlife land is owned by the White minority and by the state, with few wildlife resources on community lands.”

Critics note that these conservation disputes are unfolding amid persistent government failures to enact land reforms. “The disparities in ownership in the wildlife industry somewhat reflects what we see in other sub-sectors of agriculture, where participation of Black farmers remains marginal,” says Wandile Sihlobo, the chief economist at the Agricultural Business Chamber of South Africa and author of a recent book on land reform in the country.

As part of its vision, the government panel calls for the removal of fences separating many conservation areas. The report envisions “an authentic wild sense of place” with “larger contiguous areas containing vibrant self-sustaining populations” of elephants, buffalos, lions, leopards, rhinos, and other species.

“Are you trying to mask an economic incentive behind a conservation philosophy?”

Neil Greenwood, International Fund for Animal Welfare

That’s far from the present reality: In South Africa all megafauna except leopards are contained in fenced areas of some kind. And the government panel’s broader vision of wildness has elicited some skepticism from conservationists—and private rhino owners. In a written submission raising objections to the new policy, PROA argues that “human beings in South Africa and across the world simply do not have the luxury of a utopian concept of wild animals roaming across millions of hectares of unfenced, uninhabited, and human-free plains.”

In an email, Momberg wrote that Barbara Creecy, minister of Forestry, Fisheries, and the Environment, preferred not to comment, explaining that officials are still reviewing public responses to the proposal.

For now, Hume’s rhino breeding operation is continuing to grow. On a recent morning, Otto and other Hume employees prepared to dehorn 19 bulls—a brisk, clinical undertaking.

While the rhinos may live carefully managed lives on a ranch, they remain dangerous. Aiming a rifle-like tranquillizer gun out the window of her Toyota Landcruiser, Otto shot a dart into each rhino, generally from around 50 yards. As the rhino wobbled, a member of the up to 15-person crew pulled a blindfold over its eyes, while several men ran in to keep the animal upright. Once the rhino was lying on its chest, one of the ranch’s managers used a hand-held electric saw to do the trimming.

“We are cutting above the growth plate,” Otto said as the saw sliced through the horn of a 2-ton bull. “The section they are trimming is excess horn that contains no blood vessels or nerves.”

When the trimming was complete, Otto injected the rhino with an antidote to the tranquilizer.

“You don’t want to be next to him when he wakes up,” she cautioned. The situation was unnatural, but a rhino is a rhino.

These are the days in the year you’re more likely to hit a deer

Tom Langen is a professor of Biology at Clarkson University. This story originally featured on The Conversation.

Autumn is here, and that means the risk of hitting deer on rural roads and highways is rising, especially around dusk and during a full moon.

Deer cause over 1 million motor vehicle accidents in the US each year, resulting in more than $1 billion in property damage, about 200 human deaths and 29,000 serious injuries. Property damage insurance claims average around $2,600 per accident, and the overall average cost, including severe injuries or death, is over $6,000.

While avoiding deer—as well as moose, elk and other hoofed animals, known as ungulates—can seem impossible if you’re driving in rural areas, there are certain times and places that are most hazardous, and so warrant extra caution.

Transportation agencies, working with scientists, have been developing ways to predict where deer and other ungulates enter roads so they can post warning signs or install fencing or wildlife passages under or over the roadway. Just as important is knowing when these accidents occur.

My former students Victor Colino-Rabanal, Nimanthi Abeyrathna, and I have analyzed over 86,000 deer-vehicle collisions involving white-tailed deer in New York state using police records over a three-year period. Here’s what our research and other studies show about timing and risk.

Time of day, month and year matters

The risk of hitting a deer varies by time of day, day of the week, the monthly lunar cycle and seasons of the year.

These accident cycles are partly a function of driver behavior—they are highest when traffic is heavy, drivers are least alert and driving conditions are poorest for spotting animals. They are also affected by deer behavior. Not infrequently, deer-vehicle accidents involve multiple vehicles, as startled drivers swerve to miss a deer and collide with a vehicle in another lane, or they slam on the breaks and are rear-ended by the vehicle behind.

In analyzing thousands of deer-vehicle collisions, we found that these accidents occur most frequently at dusk and dawn, when deer are most active and drivers’ ability to spot them is poorest. Only about 20 percent of accidents occur during daylight hours. Deer-vehicle accidents are eight times more frequent per hour of dusk than daylight, and four times more frequent at dusk than after nightfall.

During the week, accidents occur most frequently on days that have the most drivers on the road at dawn or dusk, so they are associated with work commuter driving patterns and social factors such as Friday “date night” traffic.

Over the span of a month, the most deer-vehicle accidents occur during the full moon, and at the time of night that the moon is brightest. Deer move greater distances from cover and are more likely to enter roadways when there is more illumination at night. The pattern holds for deer and other ungulates in both North America and Europe.

Over a year, by far the highest numbers of deer-vehicle accidents are in autumn, and particularly during the rut, when bucks search and compete to mate with does. In New York state, the peak number of deer-vehicle accidents occurs in the last week of October and first weeks of November. There are over four times as many deer-vehicle accidents during that period than during spring. Moose-vehicle accidents show a similar pattern.

That high-risk period is also when daylight saving time ends—it happens on Nov. 7, 2021, in the US. Shifting the clock one hour back means more commuters are on the road during the high-risk dusk hours. The result is more cars driving at the peak time of day and during the peak time of the year for deer-vehicle accidents.

Overall, given that most US states and more than 70 countries have seasonal “daylight saving” clock shifts, elevated ungulate-vehicle accident rates caused by clock shift may be a widespread problem.

There is a longstanding debate about the benefit of a daylight saving clock shift, given how it disrupts humans’ circadian rhythms, causing short-term stress and fatigue. Risk of deer-vehicle accidents may be another reason to reconsider whether clock shifts are worthwhile.

Deer still cross roads at any time

It’s important to remember that deer-vehicle accidents can occur at any time of day or night, on any day of the year—and that deer can show up in urban areas as well as rural ones.

The insurance company State Farm found that on average, US drivers have a 1 in 116 chance of hitting an animal, with much higher rates in states such as West Virginia, Montana and Pennsylvania. Over the 12 months ending in June 2020, State Farm counted 1.9 million insurance claims for collisions with wildlife nationwide. Around 90 percent of those involved deer.

Where deer or other ungulates are likely to be present, drivers should always be alert and cautious, especially at dawn, dusk, on bright moonlit nights and during the fall rut.

The Conversation

Brain size isn’t everything

Ant brains are hundreds of thousands of times smaller than ours, rendering them incapable of any significant individual computing power. Instead, they employ an intricate hive mind communication system, says New Jersey Institute of Technology entomologist Simon Garnier. The bugs emit chemicals called pheromones when they encounter a resource, such as food or a nesting site. Hundreds of fellow ants follow the smell, leading to an organized army of satiated critters or the construction of a giant (relatively speaking) anthill.

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