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1018 BioScience • December 2017 / Vol. 67 No. 12 https://academic.oup.com/bioscience

BioScience 67: 1018–1025. © 2017 Cheryl Lyn Dybas. All rights reserved. doi:10.1093/biosci/bix126

The Carnivores Come to Town

CHERYL LYN DYBAS

Humans and wild predators grapple with urban coexistence

It was pitch dark at 5:32 a.m. on 29 April 2016, when an intruder

hopped over an electrical substation fence and shut down the most power-ful scientific instrument in the world, the 27-kilometer-long Large Hadron Collider (LHC) near Geneva.

The miscreant short-circuited an electrical transformer, cutting power to the LHC, the globe’s largest par-ticle physics laboratory. The LHC tunnel, where most of the experi-ments take place, is buried 100 meters underground between the Geneva International Airport and the nearby Jura Mountains. But above it runs a grid that carries enough power to sus-tain 370,000 homes for a year.

Investigations by LHC engineers revealed that cables running to a transformer had sustained severe

damage. The engineers traced every foot of a vast rabbit warren of wires. The culprit, according to the logbook: “Foreign object (weasel) located on the 66kV transformer in P8, causing severe electrical disturbance through-out the complex.” The animal, later identified as a stone or beech marten, had been electrocuted. But it managed to shut down much of the LHC for a week.

When the collider reopened, “stoat alley” was back on track, an LHC news bulletin reported—but not for long. On 21 November 2016, another mar-ten penetrated the LHC’s perimeter.

The LHC is far from the only human quarters in which martens have taken up residence. In central Europe, the animals have long made use of urban environments, according to records

dating to 1949. Most have presumably been more fortunate than those at the LHC.

As for the LHC marten of November 2016, it is on display at the Natural History Museum in Rotterdam, in the Netherlands. The exhibit: Dead Animal Tales.

Carnivores moving inAlthough stone martens may be among the more adventurous car-nivores living cheek-by-jowl with humans, the list is long and increas-ing. Red foxes, bobcats, ocelots, per-egrine falcons, raccoons, river otters, black bears, mountain lions, and other species reside in cities, towns, and villages.

Feral dogs ride Moscow subways, wild boars interrupt Berlin soccer

Wild carnivores small and large, such as this weasel, are moving into cities, and humans are heading to the suburbs. Is there a way to find a no-conflict zone? Photograph: National Park Service.

In April 2016, a short-circuit cut power to the Large Hadron Collider, the world’s most powerful scientific instrument. It was caused by a beech marten. Photograph: CERN/Margot Frenot.

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https://academic.oup.com/bioscience December 2017 / Vol. 67 No. 12 • BioScience 1019

games, and in Madison, Wisconsin, red foxes tunnel under garage floors to dig dens, according to wildlife biologist David Drake, director of the Urban Canid Project at the University of Wisconsin–Madison. Red foxes in Fairfax, Virginia, may do them one better, stealing news-papers from suburban front porches, perhaps to line their domiciles or, as one homeowner quipped, to read up on prime real estate in the neighborhood.

Urban carnivores provide endless “can you believe?” tales, but they are also the subjects of growing scientific interest, so much so that researchers have coined a term for them: syn-anthropes. Synanthropes demon-strate how quickly wild species can adapt to the pressures of living in unnatural habitats, says Drake, who discussed Madison’s red foxes at the

2017 International Urban Wildlife Conference in San Diego.

Beyond adapting, synanthropes are evolving. Some researchers believe that urban areas are accelerating that process. Changes that would usu-ally take centuries are happening in decades to years. “We are in the middle of a period of rapid and substantial environmental change,” write Thomas Newsome, of Deakin University in Victoria, Australia, and colleagues in a paper in the April 2017 issue of BioScience. “One impact of this upheaval is increasing contact between humans and other animals. As a result of increased interaction, the evolu-tion and function of many species may be altered through time via pro-cesses including domestication and hybridization.”

A major contributor to that faster evolution, states Newsome, is the

availability of human-provided food, such as trash and livestock—and handouts. For example, urban red foxes in Israel have smaller home ranges and higher survival rates than their country cousins, likely a result of easy meals. “Genetic differentia-tion has also been found between rural and urban red foxes in Zurich, Switzerland,” Newsome writes.

As people continue to convert land for agriculture and suburban or urban development, more wild carnivores are feasting on human-provided food. Climate change could exacerbate that trend, according to Newsome. As sea ice melts, polar bears are turning to birds and other terrestrial prey in lieu of their usual meals of ringed seals. Infanticide by nutritionally stressed male polar bears is on the rise, as is competition with brown bears for land-based food, including at our

Researchers affiliated with the University of Wisconsin–Madison Urban Canid Project are studying the city of Madison’s increasingly common red foxes and coyotes. Photograph: University of Wisconsin–Madison.


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trash dumps. The potential for polar bears’ habituation exists in towns such as Churchill, Manitoba, where the animals help themselves to subsi-dies of food from people.

Life in the big cityFor the first time in history, most humans live in urban areas; nearly 4 billion people reside in cities around the world. As we move into town, car-nivores are right behind—or, in some cases, people claim turf that had already been staked out by wild animals. The city of Boulder, Colorado, for example, now sprawls up nearby canyons—and smack into mountain-lion territory. Earlier this year, one homeowner looked out his living-room window and into the faces of three mountain lion cubs on his deck.

“Cities may represent one of the most challenging environments for carnivorous mammals,” state Bill Bateman, of South Africa’s University of Pretoria, and Trish Fleming, of Murdoch University, in Australia, in a 2012 paper in the Journal of Zoology.

As cities grow, these scientists believe, humans are removing carni-vores’ natural habitats. With the loss of undeveloped landscapes, urban areas are becoming more important for car-nivore conservation.

Life in the big city is not easy. Urban areas, Bateman and Fleming say, “have a dearth of vegetation and other natu-ral resources, increased habitat frag-mentation, and an abundance of roads as well as altered climate. It is therefore intriguing that several carnivore spe-cies have become established in cities across the globe.” Red foxes, coyotes, Eurasian badgers, and raccoons not only survive in cities, the biologists stated, but “they have managed to exploit anthropogenic food sources and shelter to their significant advan-tage, achieving higher population den-sities than are found under natural conditions.”

From urban avoider to urban exploiterResearchers classify carnivores as urban avoiders (those that rapidly disappear

from urbanized areas); urban adapters (those that still mostly rely on natural resources, with cities in or near their preferred habitats); and urban exploit-ers (those that seek out cities, making use of food and shelter provided by humans).

Among the best examples of an urban avoider is the tiny population of ocelots that ekes out a living in South Texas. They are the only remaining ocelots in the United States. “Ocelots almost never go near humans or our infrastructure,” says Hilary Swarts, a wildlife biologist at the Laguna Atascosa National Wildlife Refuge, in Los Fresnos, Texas, where the small cats still survive. “Ocelots can’t seem to coexist with any level of human activ-ity, development, or presence, making them unlikely to be successful urban carnivores.”

A 2014 paper published in PLOS ONE by Michael Tewes, of Texas A&M University–Kingsville, bears that out. Tewes and colleagues found that “human-induced population reduc-tions [in particular, ocelots hit on

Peregrine falcons have adapted to cities, where they live on precipices such as this building ledge in Richmond, Virginia, and hunt pigeons and other prey. Photograph: Virginia Department of Game and Inland Fisheries.


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highways] and habitat fragmentation threaten the remaining ocelots in the US.”

Urban adapters are often found in suburban and city landscapes, where they forage in trash, vegetable gar-dens, and other resources humans provide. Medium-size carnivores such as coyotes and red foxes, also called mesopredators, are often urban adapters. Much of their success stems from their diets; they are far from picky eaters. They trot along, carry-ing everything from discarded fast-food wrappers to fisheries bycatch that washes ashore. In addition to abundant food sources, the elimina-tion of large urban predators such as mountain lions has given smaller carnivores free rein.

When populations of apex predators such as mountain lions and wolves decrease, mesopredators such as red foxes and coyotes often increase. High mesopredator numbers, however, may lead to declining populations of their bird and rabbit prey.

Urban exploiters, the species most at home with humans, have adapted well to cities and include carnivores such as peregrine falcons. In the wild, the fal-cons live on steep, rocky precipices; in downtown districts, they readily make their homes atop cliff-like buildings.

“Towns and cities offer abundant food for peregrines,” says Bryan Watts, director of the Center for Conservation Biology at the College of William and Mary, in Williamsburg, and Virginia Commonwealth University,

in Richmond. “Urban peregrines look for places where they can catch birds [like pigeons] and ledges where they can pluck and eat them.” For exam-ple, the falcons have long nested atop Richmond’s Riverfront Plaza building.

Peregrines may be changing in response to city life. Researchers in the United Kingdom have found urban falcon eyries lined with bat remains. This suggests that the falcons are mov-ing, at least in part, from diurnal to nocturnal hunting.

The line from urban avoider to adapter to exploiter is not clear cut, ecologists say, and is shifting with urban sprawl. For example, black bears, once thought of as urban avoid-ers, are becoming urban adapters. Scientists in Connecticut and other

A mink will walk a metaphorical plank to get to water, crossing yards, streets, parking lots, ditches, and even sewers. Photograph: Needsmoreritalin.


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states are finding increasing black-bear densities in suburban neighbor-hoods, according to a recent report by Tracy Rittenhouse, of the University of Connecticut, in the journal Landscape and Urban Planning.

Then there are the wolves.

Wolves at the doorGray wolves once existed throughout North America and Eurasia, but little by little, they were driven into remote areas. Then, protection of the spe-cies resulted in increasing numbers in mainland Europe and elsewhere. Wolves now frequent refuse dumps in Israel, Italy, and Romania. In Canada, they follow dump trucks carrying trash to landfills, timing their appearance to that of the trucks.

“Biologically, wolves can and will live almost anyplace people will toler-ate them, and that varies with local culture and politics,” writes wolf biolo-gist David Mech, of the US Geological Survey’s Northern Prairie Wildlife Research Center and the University

of Minnesota, in a 2017 paper in the journal Biological Conservation.

If past is prologue, Mech might have guessed that wolves would someday arrive near his hometown of Minneapolis. In 2004, he pub-lished a paper in The Canadian Field-Naturalist on mink and river otters making their way across an urbanized area: Lauderdale, Minnesota, on the border of Minneapolis. There, Mech encountered the mustelids walking a metaphorical plank. To get to the area’s only water—a pond in the mid-dle of a golf course—the animals “had to pass through yards, streets, high-ways, parking lots, ditches and possi-bly sewers,” he wrote. “These findings document the great adaptability of these species.”

Suburban wolvesIn the spring of 2015, gray wolves showed up near Isanti, Minnesota, 45 minutes from downtown Minneapolis. It is the farthest south in the state a pack of wolves has been

found, Mech says. The wolves thrived on the area’s abundant deer and had a litter of pups.

“I see no reason why wolves could not live in cities, except that people would not let them,” Mech says. “As wolves began to inhabit sub-urbs, they would kill dogs and deer and scare people, and citizens would insist on their removal.” How right he was.

As the Isanti wolf pack grew, their human neighbors began to report problems to wildlife officials. The wolves killed domestic ani-mals, city residents claimed. The US Department of Agriculture (USDA)’s Wildlife Services Division, which has the authority to respond to reports of “problem wildlife,” removed some of the wolves.

Isanti resident Larry Hogie digs soil from ponds on his property, which he forms into mounds of dirt for sale to gardeners and horticulture centers. One day, Hogie glanced at the edge of the woods near his home and into

Minnesota’s far northern gray wolves are moving southward, reaching places less than an hour from downtown Minneapolis. Photograph: Larry Hogie.


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the eyes of a gray wolf. “Like any other animal,” he says, “wolves like to be where they can see what’s going on, so they’ve been sitting on top of my dirt mounds.”

Hogie’s neighbors lost dogs, possibly to the wolves. “The wolves may not have a future in this community,” he says.

Europe may be ahead of other places in figuring out how to coexist with carnivores. Results reported in a 2014 paper in Science show that humans and predators in fact can successfully share the landscape.

By the early twentieth century, carnivores had been exterminated from most of Europe, with relict populations persisting. Now, there are stable or increasing populations of brown bears, Eurasian lynx, wol-verines—and wolves, says Guillaume Chapron, of the Swedish University of Agricultural Sciences, lead author of the Science paper. These species do not live in remote wilderness areas but in human-dominated landscapes.

There is a big difference in strategies to conserve carnivores in Europe ver-sus those in other parts of the world, says Chapron. Carnivores outside Europe are mainly protected in large national parks or wilderness areas, separated from people. “If Europe had used that model,” Chapron maintains, “we would hardly have any carnivores

because there are not enough large areas of wilderness remaining.”

Instead, in areas where wolves and other carnivores might prey on live-stock, he says, installing electric fences and employing livestock-guarding dogs can facilitate coexistence. Could these tactics work in the United States? As more residents of states such as New Hampshire raise chick-ens in their backyards, carnivores are increasingly recognizing unprotected poultry as easy food sources. And each year, “more wildlife is killed by homeowners protecting chickens and other livestock from predation,” says Andrew Timmins, a biologist at the New Hampshire Fish and Game Department. “This does not represent a sustainable approach to managing wildlife. If poultry and livestock owners were willing to take

Further reading.

Gehrt SD, Riley SPD, Cypher BL, eds. 2010. Urban Carnivores: Ecology, Conflict, and Conservation. Johns Hopkins University Press. (2 October 2017; https://jhupbooks.press.jhu.edu/content/urban-carnivores)

Janecka JE, Tewes ME, Laack L, Caso A, Grassman LI, Honeycutt RL. 2014. Loss of genetic diversity among ocelots in the United States during the 20th century linked to human induced population reductions. PLOS ONE (art. e89384). (2 October 2017; https://doi.org/10.1371/journal.pone.0089384)

University of Wisconsin–Madison Urban Canid Project. (2 October 2017; http://uwur-bancanidproject.weebly.com)

proactive precautions, there would be no need to remove a potential threat.”

Electric fencing is the most effec-tive means of keeping predators out of chicken coops and similar areas, accord-ing to New Hampshire Fish and Game Department documents. “Be respon-sible,” says Timmins, “go electric!”

Where carnivores can (sometimes) peacefully live: Long Island’s red foxesRed foxes are the most widespread, and possibly most abundant, urban carnivore in North America, Australia, Europe, and Japan, state Carl Soulsbury, of the University of Bristol in the United Kingdom, and coauthors in the book Urban Carnivores: Ecology, Conflict, and Conservation.

Red foxes are the most widespread urban carnivores in North America, Australia, Europe, and Japan. Shown here, a fox in the shadow of Islip, New York. Photograph: Virginia Polytechnic Institute and State University.

Suburban and urban foxes often subsist on human handouts, including fast-food leftovers. Photograph: Virginia Polytechnic Institute and State University.


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A golden jackal at a trash dump in Eastern Europe. The jackals are performing an ecosystem service for humans, carrying away millions of rodents and other pests each year. Photograph: Miha Krofel.

Just ask wildlife biologist Sarah Karpanty, of Virginia Polytechnic Institute and State University in Blacksburg. Karpanty is conducting a multiyear study of red-fox population density, spatial ecology, and dietary ecology on Fire Island, New York. Her research territory extends from Robert Moses State Park at one end of the island to Fire Island National Seashore on the other. How the foxes got there, no one is sure, but they probably made their way across the 13-kilometer-long Robert Moses Causeway that connects the bustling town of Islip with Fire Island.

How many foxes make a living on Fire Island, and how do they do it? From a 2016 survey, Karpanty esti-mates that between Fire Island Inlet at

the island’s western end and Old Inlet at its eastern end, there are 39 adults and 57 kits. For the entire island, Karpanty says, there are some 2.37 adults and 3.51 kits per square kilo-meter, in a total area of 16.18 square kilometers.

“In other words,” she sums up, “a lot of foxes!” The numbers are similar to those of other fox-rich locales from Edinburgh, Scotland, to Melbourne, Australia, according to Urban Carnivores.

In suburban Islip’s backyard, foxes are living high, although not always on the healthiest diets. “We’ve found everything at dens from take-out food wrappers to chip bags,” Karpanty says. The foxes have also left feathers and fish scales at den “doors.” Local (human) fishers often discard skates as

trash fish. The skates then wash up on beaches, where the foxes make off with fish parts.

“These foxes are also into ‘begging’ behavior like what you might see in your dog,” says Karpanty. Red foxes haunt the main road running up and down Fire Island, stopping to look at cars passing by to see if the humans within will offer handouts. During recent fieldwork, Karpanty watched while car occupants rolled down the windows and tossed a scrap to a wait-ing fox, who ran for it. “Obviously, this isn’t a good thing,” says Karpanty.

Accepting handouts can have disastrous results. In January, a fox that chased cars for food in Robert Moses State Park was fatally shot by a man with a crossbow. The dead fox


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was a mature female that was part of Karpanty’s study. “We’re asking visi-tors to the island to please not feed the foxes—nor any wildlife,” says Karpanty. “If people like the foxes, the best thing they can do is place their leftovers in the nearest trash can, not on the road.”

Symbiotic urban carnivores?If “waste management” is a challenge on Fire Island and throughout the United States, it is no less so in Serbia and across the human-dominated landscapes of Europe. But Duško Ćirović, of the University of Belgrade, and his colleagues discovered a solu-tion almost in front of their eyes. As they reported in a 2016 paper in

Biological Conservation, golden jackals are serving as unpaid trash collectors.

From the contents of 606 golden jackal stomachs, as well as the jack-als’ food intake and population size, the researchers estimate that in Serbia alone, jackals annually remove more than 3700 tons of trash and other waste and 13.2 million crop-pest rodents. The biologists found that in their study area, the monetary value of the jackals’ waste removal is greater than €500,000 per year. “We scaled this up to evaluate golden jackals’ ecosys-tem services at the continental scale,” write Ćirović and colleagues in their paper. Continent-wide, the jackals annually remove substantial amounts

of discarded animal waste (more than 13,000 tons) and potential crop pests (more than 158 million rodents).

These results, says Ćirović, “are the first to demonstrate the value of eco-system services provided by mesocar-nivores as scavengers, and show that these predators are of great value to local communities in the modern world.”

Coexist or perish? It is a question that could be asked across the globe about urban carnivores.

Science journalist Cheryl Lyn Dybas ([email protected]), an ecologist and fellow of the

International League of Conservation Writers, often writes for BioScience on conservation

biology topics.


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