Light pollution alters predator-prey interactions between cougars and mule deer in western US

A new study provides strong evidence that exposure to light pollution alters predator-prey dynamics between mule deer and cougars across the intermountain West, a rapidly growing region where nighttime skyglow is an increasing environmental disturbance.

The University of Michigan-led study, published online Oct. 18 in the journal Ecography, is the first to assess the impacts of light pollution on predator-prey interactions at a regional scale. It combines satellite-derived estimates of artificial nighttime lights with GPS location data from hundreds of radio-collared mule deer and cougars across the intermountain West.

The study found that:

• Mule deer living in light-polluted areas are drawn to artificial nighttime lighting, which is associated with green vegetation around homes.
• Cougars, also known as mountain lions and pumas, are able to successfully hunt within light-polluted areas by selecting the darkest spots on the landscape to make their kill.
• While mule deer that live in dark wildland locations are most active around dawn and dusk, those living around artificial night light forage throughout the day and are more active at night than wildland deer--especially during the summer.

The animal data used in the study were collected by state and federal wildlife agencies across the region. Collation of those records by the study authors yielded what is believed to be the largest dataset on interactions between cougars and mule deer, two of the most ecologically and economically important large-mammal species in the West.

"Our findings illuminate some of the ways that changes in land use are creating a brighter world that impacts the biology and ecology of highly mobile mammalian species, including an apex carnivore," said study lead author Mark Ditmer, formerly a postdoctoral researcher at the University of Michigan School for Environment and Sustainability, now at Colorado State University.

The intermountain West spans nearly 400,000 square miles and is an ideal place to assess how varying light-pollution exposures influence the behavior of mule deer and cougars and their predator-prey dynamics. Both species are widely distributed throughout the region--the mule deer is the cougar's primary prey species--and the region presents a wide range of nighttime lighting conditions.

The intermountain West is home to some of the darkest night skies in the continental United States, as well as some of the fastest-growing metropolitan areas, including Las Vegas and Salt Lake City. Between the dark wildlands and the brightly illuminated cities is the wildland-urban interface, the rapidly expanding zone where homes and associated structures are built within forests and other types of undeveloped wildland vegetation.

For their study, the researchers obtained detailed estimates of nighttime lighting sources from the NASA-NOAA Suomi polar-orbiting satellite. They collected GPS location data for 117 cougars and 486 mule deer from four states: Utah, Arizona, Nevada and California. In addition, wildlife agencies provided locations of 1,562 sites where cougars successfully killed mule deer.

"This paper represents a massive undertaking, and to our knowledge this dataset is the largest ever compiled for these two species," said study senior author Neil Carter, a conservation ecologist at the U-M School for Environment and Sustainability.

Deer in the arid West are attracted to the greenery in the backyards and parks of the wildland-urban interface. Predators follow them there, despite increased nighttime light levels that they would normally shun. Going into the study, the researchers suspected that light pollution within the wildland-urban interface could alter cougar-mule deer interactions in one of two ways.

Perhaps artificial nighttime light would create a shield that protects deer from predators and allows them to forage freely. Alternatively, cougars might exploit elevated deer densities within the wildland-urban interface, feasting on easy prey inside what scientists call an ecological trap.

Data from the study provides support for both the predator shield and ecological trap hypotheses, according to the researchers. At certain times and locations within the wildland-urban interface, there is simply too much artificial light and/or human activity for cougars, creating a protective shield for deer.

An ecological trap occurs when an animal is misled, or trapped, into settling for apparently attractive but in fact low-quality habitat. In this particular case, mule deer are drawn to the greenery of the wildland-urban interface and may mistakenly perceive that the enhanced nighttime lighting creates a predator-free zone.

But the cougars are able to successfully hunt within the wildland-urban interface by carefully selecting the darkest spots on the landscape to make their kill, according to the study. In contrast, cougars living in dark wildland locations hunt in places where nighttime light levels are slightly higher than the surroundings, the researchers found.

"The intermountain West is the fastest-growing region of the U.S., and we anticipate that night light levels will dramatically increase in magnitude and across space," said U-M's Carter. "These elevated levels of night light are likely to fundamentally alter a predator-prey system of ecological and management significance--both species are hunted extensively in this region and are economically and culturally important."

Carnivores living near people feast on human food, threatening ecosystems

 Ecologists at the University of Wisconsin-Madison have found that carnivores living near people can get more than half of their diets from human food sources, a major lifestyle disruption that could put North America's carnivore-dominated ecosystems at risk. The researchers studied the diets of seven predator species across the Great Lakes region of the U.S. They gathered bone and fur samples for chemical analysis from areas as remote as national parks to major metropolitan regions like Albany, New York. They found that the closer carnivores lived to cities and farms, the more human food they ate.

While evolution has shaped these species to compete for different resources, their newfound reliance on a common food source could put them in conflict with one another. That conflict could be reordering the relationship between different carnivores and between predators and prey, with an unknown but likely detrimental impact on ecosystems that evolved under significant influence of strong predators.

Jon Pauli, a UW-Madison professor of forest and wildlife ecology, and his former graduate student Phil Manlick, published their findings this week in the Proceedings of the National Academy of Sciences. The study is the most comprehensive look yet at how most of the region's major carnivores -- like gray wolves, coyotes, and bobcats -- have changed their diets in response to people.

How much human food they ate varied considerably by location. On average, more than 25 percent of the carnivores' diets came from human sources in the most human-altered habitats.

It also varied by species. For instance, committed carnivores like bobcats ate a relatively small amount of human food. "But what you see is that the sort of generalist species that you might expect -- coyotes, foxes, fishers, martens -- in human-dominated landscapes, they're getting upwards of 50 percent of their diet from human foods," says Manlick, the lead author of the study who is now a postdoctoral researcher at the University of New Mexico. "That's a relatively shocking number, I think."

Pauli and Manlick found that relying on human food sources increased how much carnivores overlapped one another in their competition for food. Compared to when these predators vie for distinct prey, this increased competition could lead to more conflicts between animals. Their reliance on human food could also make the carnivores vulnerable to human attacks near towns, or even change how and when they hunt traditional prey, with potentially harmful ecological consequences.

The researchers studied the diets of almost 700 carnivores, including red and gray foxes, fishers, and American martens. They gathered bone and fur samples from Minnesota, Wisconsin, New York and the Upper Peninsula of Michigan with the help of state and federal researchers and citizen-science trappers. The researchers compared the carnivores' diets to the extent of human development in the region, which varied from essentially pristine wilderness to urban sprawl.

Thanks to quirks in how plants incorporate carbon as they grow, a sample of bone or fur is enough to get a snapshot of an animal's diet. Different weights, or isotopes, of carbon are common in different plants -- and in the animals who ultimately eat them.

"Isotopes are relatively intuitive: You are what you eat," says Manlick. "If you look at humans, we look like corn."

Human foods, heavy in corn and sugar, lend them distinctive carbon signatures. In contrast, the diets of prey species in the wild confer their own carbon signatures. The ratio of these two isotope fingerprints in a predator's bone can tell scientists what proportion of their diet came from human sources, either directly or from their prey that ate human food first.

The geographic extent of the study and the large number of species the ecologists examined demonstrate that the trend of human food subsidies in carnivore diets is not limited to a single location or species. The ultimate outcome of such widespread disruptions remains unclear.

"When you change the landscape so dramatically in terms of one of the most important attributes of a species -- their food -- that has unknown consequences for the overall community structure," says Pauli. "And so I think the onus is now on us as ecologists and conservation biologists to begin to understand these novel ecosystems and begin to predict who are the winners and who are the losers."

Red fox displaces Arctic fox thanks to littering

Trash draws scavengers to places they might not otherwise go

NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

Research News

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IMAGE: THE DENSITY OF RED FOXES IS INCREASING IN NORWAY'S MOUNTAINOUS AREAS. THE MORE TRASH AND FOOD WASTE RED FOXES HAVE ACCESS TO, THE GREATER THEIR NUMBERS. THIS PHOTO WAS TAKEN... view more 

CREDIT: NINA, GAME CAMERA

Animal species that are at home in the high mountains are finding their habitats reduced and fragmented by roads. In addition, they face competition from scavengers from lower boreal areas that find their way to the mountains.

"More cabins, more tourism and increased car traffic means more litter and more roadkill. For the red fox, the crow and other scavengers, it means more tempting food," says Lars Rød-Eriksen, who is employed as a researcher in terrestrial ecology at NINA, the Norwegian Institute for Nature Research.

In his doctoral work at the Norwegian University of Science and Technology (NTNU), Rød-Eriksen surveyed road segments at Dovre, Saltfjellet and Hardangervidda to learn how wildlife is affected by the highways.

Roads = food

"We found that the red fox uses the road both to find food and to move from place to place. Especially in the winter, using the roadways is easier than travelling across the snowy terrain," he says.

"Using tracks in the snow and game cameras, we were able to document that the density of red foxes increases the closer to the road one gets. The more litter and food waste they have access to, the greater the number of red foxes that find their way to the area."

The researcher notes that the pattern is the opposite for Arctic foxes. "A lot of trash means few Arctic foxes. We found that the Arctic fox doesn't tend to stay close to the road. This is probably not because the they aren't attracted to the road, but because the presence of the red fox makes them keep their distance."

Weaker species displaced

Small rodents are the Arctic fox's specialty fare, but it isn't "too fussy" to eat trash. In competing with the red fox, however, it falls short.

"The Arctic fox is also attracted to roads, but the red fox is bigger and dominates in the competition between the species. There are also examples of red foxes that have killed Arctic foxes. Increased access to food enables the red fox to establish itself in the high alpine zone. The search for food is especially intense in late winter," Rød-Eriksen says.

The crow is both a competitor and a useful helper for the fox. Often crows are the first to discover a treat, but foxes are observant and use the crows to guide them to where the food is.

Unwelcome in the mountains

"The red fox has existed in the mountains before. But it's an invasive species and can disrupt the natural alpine ecosystem if it establishes itself there permanently, like it seems to be doing now. The Arctic fox is already an endangered species, and it seems likely that the red fox is impacting other alpine species as well, such as ptarmigan, that are ground nesters. We call it a cascade effect when several species are affected," says Rød-Eriksen.

How about a litter law?

More roads and increased traffic also mean more roadkill. Rød-Eriksen believes it's easier to tackle the littering problem than the roadkill.

"Information campaigns can inform people about the consequences of throwing out and leaving trash and food scraps behind. A lot of people probably don't give any thought to how littering can negatively impact wildlife. Other countries have stricter legislation against littering. Maybe Norway should also consider it. Personally, I think it would be effective," says Rød-Eriksen.  

To record the movements of red foxes and Arctic foxes during the winter, Rød-Eriksen used tracking, supplemented by a game camera with bait at different distances from the road. These methods yielded good and reliable findings.

Summertime proved more difficult. The crows found the prey before the fox and often managed to eat it before the fox could get to it. Rød-Eriksen also placed artificial bird nests containing a real quail egg and a fake egg made from modelling clay along the transects.

The idea was that bite marks in the fake, soft egg would reveal whether a fox or a crow had tried to eat it. Here too, the crow created problems that made the results less reliable during the summer. Rød-Eriksen plans to take a closer look at seasonal variations and more comparable methods in future studies.

What do lynx, flying squirrels, ravens, and wolverines have in common?

They will all scavenge from snowshoe hare carcasses under the right conditions, according to a new study by University of Alberta ecologists. And they're not alone. In fact, researchers documented 24 different species feeding from snowshoe hare carcasses in Canada's northern boreal forest.

"This is one of the most diverse scavenger communities recorded," said lead author Michael Peers, who conducted this research during his PhD studies under the supervision of ProfessorStan Boutin in the Department of Biological Sciences.

"Species we may think of as scavengers like common ravens, magpies, and wolverines were recorded, but also species that people might not expect to be scavengers. We documented snowshoe hares, Canada lynx, red squirrels, Northern flying squirrels, arctic ground squirrels, and chipmunks all scavenging."

The researchers examined the northern boreal forest in the Yukon over a four-year period from 2015 to 2018. Using remote sensing cameras, the researchers examined which animals scavenged from nearly 100 opportunistically placed snowshoe hare carcasses throughout the region.

The results indicate that prey species may have a more complex impact on food webs than previously thought, because their numbers influence both their direct predators as well as other animals who commonly scavenge.

"Scavenging by animals can have important impacts on food webs, but is often overlooked in food web research," explained Peers. "Our data shows that a lot of species scavenge in the boreal forest of Canada, and that changing temperatures or the abundance of keystone species can impact scavenging communities."

Industry-made pits are beneficial for beavers and wolverines

In Northern Alberta, pits created by industry activity may support beavers and subsequently wolverines

UNIVERSITY OF ALBERTA

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IMAGE: BEAVERS, LIKE THE ONE PICTURED HERE, ARE MAKING THEIR HOMES ON SITES OF INDUSTRY ACTIVITY. IMAGE CREDIT: A. COLTON. view more 

CREDIT: A. COLTON.

Beavers and wolverines in Northern Alberta are using industry-created borrow pits as homes and feeding grounds, according to a new study by University of Alberta ecologists.

The research examined the relationship between local wildlife and borrow pits, which are industry-created sites where material such as soil, gravel, or sand has been dug up for road construction. The results show that when revegetated the sites provide homes for beavers, which in turn support the survival of wolverines.

"The borrow pits enhance habitats for a number of species of wildlife in the bogs of Northern Alberta," said Mark Boyce, co-author on the paper, professor in the Department of Biological Sciences, and Alberta Conservation Association Chair in Fisheries and Wildlife.

"The deep water and adjacent forage create excellent habitats for beavers. And wolverines thrive when beavers do. Not only do they prey on beavers, wolverines also have been shown to use beaver lodges as dens where they have their cubs."

The displacement of wildlife by industrial development is a complex issue, Boyce explains. "In this case, industrial development created the borrow pits that are now used by beavers that actually enhances habitats for our wilderness icon, the wolverine."

The research was led by PhD student Matthew Scrafford, who formed a partnership with the Dene Tha First Nation that proved instrumental for the study.

"The most important partner on this research was the Dene Tha First Nations," said Boyce. "Several young people in the area were enthusiastic about the project. They were instrumental in building traps and supporting our research."

No evidence that predator control will save mountain caribou

Addressing potential threats from predators has not slowed the dramatic decline of mountain caribou in British Columbia and Alberta, according to a new study by scientists from the University of Alberta and two other western Canadian universities.

Biologists reassessed data from research published in the Proceedings of the National Academy of Sciences (PNAS) in 2019. The original research has been cited as showing that killing wolves and fencing pregnant caribou are solutions to saving the endangered animals.

The scientists looked closely at the data provided in the 2019 study, and found that when routine statistical tests were included, predator control lacked statistical support. They found that some of the steepest declines in caribou populations were in southern British Columbia, areas where wolves are not major caribou predators.

"No matter how you calculate it, the statistics don't back up culling wolves or fencing in caribou," said Viktoria Wagner, assistant professor in University of Alberta's Department of Biological Sciences and co-author.

Instead, the authors found that statistically caribou declines tracked closely with specific mountain caribou ecotypes. The deep-snow mountain caribou found from Wells Gray Park into the Kootenays experienced the steepest declines despite having a low number of caribou killed by wolves.

"This means something is going on that's killing off an endangered species and it isn't being addressed by predator management," said Toby Spribille, assistant professor in the Department of Biological Sciences and co-author on the study. He noted that although focusing on predator threats is simple and easy to communicate, it does not capture the interactions that are causing mountain caribou to go extinct. For instance, the loss of habitat to logging, snowpack variation and snowmobiling are factors that need to be addressed, the authors say.

"This is an uncomfortable conversation to have but it should not be left out of scientific models," noted Spribille."If decision-makers are going to be serious about species conservation, it's really critical that they get all the information."

"Forests provide caribou with refuge from wolves and separation from other prey animals, including elk, moose, and deer," said Lee Harding, retired Canadian Wildlife Service biologist and lead author on the study. "Without them, caribou must constantly be on the move to find food, exposing them on all sides. Predators are just one of the hazards."

Chris Darimont, professor at University of Victoria, Mathieu Bourbonnais, assistant professor at University of British Columbia Okanagan, and Andrew Cook, PhD student in UAlberta's Department of Biological Sciences, collaborated on this research.

Are protected areas effective at maintaining large carnivore populations?

UNIVERSITY OF HELSINKI

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IMAGE: BROWN BEAR IN EASTERN FINLAND. INTERESTINGLY, THE EFFECTS OF PROTECTED AREAS ON BEAR DENSITIES VARIED DEPENDING ON THE METHODOLOGY USED. view more 

CREDIT: DANIEL BURGAS-RIERA

A recent study, led by the University of Helsinki, used a novel combination of statistical methods and an exceptional data set collected by hunters to assess the role of protected areas for carnivore conservation in Finland.

Overall, protected areas do not harbour higher densities of large carnivore species than unprotected lands. These areas even had declining wolverine densities within their limits while populations outside remained overall stable over a 30-year study period. The study was published in the journal Nature Communications.

The international group of authors, led by Dr Julien Terraube from the Faculty of Biological and Environmental Sciences at the University of Helsinki, proposes that the results do not indicate that protected areas are unimportant for carnivore conservation, as they may support seasonal habitats and prey for these highly mobile species. However, the outcomes highlight complex socio-ecological pressures on carnivore populations that vary in both time and space and affect the conservation outcomes of protected areas. For example, the largest Finnish protected areas are located in Lapland, and due to their sizes these areas are most suitable for large carnivores. However, the areas seem unable to maintain stable wolverine populations, which may be linked to increased conflicts with herders in the reindeer husbandry area.

"Wolverines are only found in three Nordic countries within the European Union, and therefore Finland plays an important role for the conservation of this species", explains Dr Terraube. He adds: "The negative trend of wolverine populations inside northern protected areas is alarming and highlights that further research is needed to understand the dynamics of wolverine populations in Lapland, how this species is affected by illegal killing and what protected areas could do to improve this situation".

On a brighter note, the researchers also found lynx densities to be higher within protected areas located in eastern Finland than those located in the western part of the country. The ecological factors that may influence this, such as prey abundance or connectivity to healthy Russian populations, remain unexplored.

The po­ten­tial of cit­izen science for as­sess­ing the im­pact of pro­tec­ted areas

The results show that counterfactual approaches applied to long-term and large-scale data are powerful analytical tools for evaluating the effectiveness of protected areas in maintaining wildlife populations. A counterfactual approach means comparing protected and unprotected sites that have similar environmental characteristics or human-caused threats. The method has been increasingly used to assess the effectiveness of protected areas in halting deforestation. This allows researchers to isolate the effect of protection on land cover from other confounding factors such as elevation. Until now, these types of approaches focused on matching analyses have been restricted to studies investigating the effects of protected areas on land-use changes. Finding wildlife time series with enough temporal and spatial coverage to conduct such robust effectiveness assessments is often difficult.

Dr. Terraube explains: "We were able to use data collected through the Finnish Wildlife Scheme to conduct this study. Hunters throughout the country have collected this data set since 1989, offering a fantastic opportunity to apply matching analyses to wildlife data for the first time and to assess large-scale and long-term patterns of protected area effectiveness. We chose to focus on large carnivores, as this species group is particularly prone to rising conflicts with local communities. Carnivore-human conflicts have increased in Finland following the recent recovery of most carnivore species. This has resulted in increasingly negative attitudes towards certain species, such as the wolf, and to increased levels of illegal killing".

Main­stream­ing im­pact eval­u­ation: to­wards bet­ter man­age­ment of pro­tec­ted areas

The study highlights the need to design robust methodological tools to strengthen our understanding of conservation outcomes and opens new avenues for improving protected area impact assessments. This is of the utmost importance, as the international community is currently turning to the post-2020 targets drafted by the UN Convention on Biological Diversity aiming to upgrade protected areas in an attempt to halt global biodiversity loss.

"We argue that this study shows that, despite methodological challenges, robust assessments of protected area effectiveness for the conservation of wide-ranging species, such as large carnivores, are possible and greatly needed as a basis for further research. It also highlights the extraordinary value of long-term wildlife monitoring activities conducted by citizens across an entire country", concludes Dr Terraube.