Why urban animals are taking the night shift

As COVID-19 forced the country into lockdown in early 2020, Chris Hansen was in the midst of his dissertation work, surveying the abundance of wildlife across western Montana. Over the course of four years, Hansen had deployed and redeployed motion-activated cameras from the suburbs of Missoula to wild areas 200 miles outside the city. His fieldwork had been cut short by the pandemic, but he had what he needed: more than a million photos, many of wildlife, but many others that didn’t particularly help with his research. 

“Just imagine someone playing catch with their dog in front of a camera,” Hansen said. “Sometimes it’ll be tens of thousands of photos.”

Later in his new workspace, the living room of his small apartment, Hansen began taking a closer look at the data he had collected. Missoula is known for having a healthy population of black bears, but something stood out about the black bear photos he’d collected. Hansen noticed his photos of bears in the woods were typically during the day, but just about every picture of a bear in town was at night. And so, sitting in his recliner, working from a laptop with a sleeping baby on his chest, Hansen compiled a figure comparing urban bear activity to activity in the wild. His hunch was correct, and his findings align with a phenomenon researchers across the globe have observed in mammal species, including black bears. Mammals are becoming increasingly nocturnal in urban environments to limit interaction with humans.    

“It’s a way for species to coexist with humans, rather than just being completely pushed out of an area,” Hansen said. 

As wild habitats continue to shrink globally, researchers like Hansen are beginning to shift their focus to urban environments to understand how species are making use of developed areas, and the ways in which cities are impacting wildlife behavior. A recent study from researchers at the University of California, Berkeley, and Boise State University found that, similar to black bears, mammals all over the world are increasing their nocturnal activity in response to man-made environments. The study encompassed 62 different mammal species and observed a shift toward nighttime activity in a large majority of species living in and around urban areas. As animals become less able to separate themselves by space from humans, they are separating themselves by time instead.

‘AFTER THE BARS CLOSE’

John Rietman lives in Missoula’s Lincolnwood neighborhood in the Upper Rattlesnake area. Residents in the neighborhood are accustomed to living with wildlife literally in their backyard, as they live on the edge of the city suburbs. Rietman was wheeling his trash can out of the garage down his sloped 30-foot driveway before the sun had come up on a cool fall morning in 2020. He knew he couldn’t put his trash out the night before because it would likely be rummaged by the time the garbage truck arrived. That particular morning, it didn’t matter. As Rietman made the short walk back to his garage, he turned and saw what he described as the biggest black bear he had ever seen.

“On all fours its shoulder was halfway up my Subaru Forester windows,” Rietman said.

He watched from his garage as the bear pulled a bag of fish guts out of the trash, maybe 30 seconds after he had wheeled it out. Rietman has lived in the neighborhood since 2006 and has seen plenty of bear activity since moving in. Just last fall, he captured images on a motion-activated camera of bears walking past his front doorstep in the darkest hours of the night. 

“After the bars close, we get nobody coming by up here,” he said. He thinks the bears know when the traffic is thin, and that it’s precisely that lack of human presence that may be one of the major factors shifting black bears toward nighttime activity in urban areas.  

A 2019 study tracking black bear movements across the state of Massachusetts observed activity indicating bears perceived humans and their associated noise and traffic as risky, but weren’t necessarily averse to human infrastructure. That makes sense considering that roadway collisions are one of the leading causes of death for bears and other wild mammals entering urban areas. Bears are seemingly shifting their most active hours to the time of day humans are most inactive. The study also found that bears living near human development were less afraid than rural bears to enter urban areas, indicating they are becoming accustomed to living in more urbanized areas. 

“There’s only certain species that are going to have the ability to actually modify when they are becoming most active. I’m just steadily more and more surprised to see how adaptable some species have become.”

Mason Fidino, quantitative ecologist at the Urban Wildlife Institute in Chicago

There is certainly a lot to like about the suburbs for many animals. In particular, there is food. Whether it’s trash, freshly watered flowers, rodents, livestock or vegetables from a garden, there is no shortage of feeding opportunities. But does the reward outweigh the risk? And can that risk be lowered by foraging at night? Montana Fish, Wildlife and Parks bear management specialist Jamie Jonkel says black bears in Missoula will do their feeding “forays” and travel through the night. He explains that irrigated lawns and well maintained foliage are a real temptation for black bears. 

“Some bear looks down and sees this lush green square down in the bottom of the valley, especially in the fall months, you know, the late summer months, when it’s just dry as a bone,” Jonkel says.

Not all mammals are on a level playing field when it comes to making use of urban ecosystems. Size, genetic makeup and human perception all factor into a species’ ability to adapt. 

Leonardo Ancillotto is a postdoctoral researcher at the University of Naples Federico II in Italy, and co-authored a study on what traits might best suit mammals visiting and residing in urban environments. He explains that cities can have a “filtering effect” on species depending on what traits they possess. “Urbanization represents a ‘novel’ pressure to wildlife,” Ancillotto writes via email. “Some species may have some traits/characteristics that allow them to cope with such new pressure, while some may not.”

Bats with long, narrow wings, for example, are found much more readily in urban environments than other bat species. A trait that was developed for flying high over grasslands and hunting insects also happens to serve them well in cities. Another major factor that comes into play for wildlife is: How will a human respond to them? A bear, mountain lion or coyote seen in the suburbs would likely be met with an unwelcoming response from humans, while a deer, squirrel or raccoon may go unnoticed.

‘HUMAN SHIELD HYPOTHESIS’

While many mammals are shifting to a nighttime schedule to avoid humans in urban areas, at least one species may be doing the opposite. Red foxes are not especially uncommon in urban settings, but they have traditionally used the hours around dawn and dusk to feed and travel. But researchers nationwide have noticed red foxes becoming increasingly active during daylight hours in urban environments. Animals living in urban environments have to balance the dangers that humans present with those presented by natural predators. For the red fox, that is often a coyote, a species that is extremely nocturnal in urban areas. Scientists think red foxes are increasingly choosing to use daylight hours to avoid interaction with their predator, the coyote. The “human shield hypothesis” explains the phenomenon. Essentially, humans could potentially act as a buffer between predators and prey. Red foxes may not perceive humans to be as dangerous as coyotes and are choosing to “shield” themselves from their natural predator by becoming more active during the day.    

Every mammal species has a different response to urbanization, and scientists are still learning what kind of impacts those adaptations may have. With many mammal species altering their activity to the nighttime, it could be that human-wildlife conflicts are reduced. On the other hand, increasing nocturnal activity in species that are typically active during the day raises a host of questions about wildlife community dynamics. Apex predators may lose their ability to hunt prey species living in urban areas or to stash a kill near human development during the daytime. Species may shift their diet toward food that is more accessible at night, changing the way certain species relate and survive off one another. Such changes have the potential to reshape entire ecological communities.    

Darwin’s theory of evolution through natural selection says that organisms which are better adapted to their environment will tend to survive and produce more offspring. With rapid urbanization happening in areas around the globe and many species being forced to learn how to navigate urban environments, humans may be imposing what is known as artificial selection on wildlife. As many mammal species shift their activity to the night in urban environments, natural selection may eventually alter species’ morphological and behavioral traits toward characteristics that are better suited for the night. 

Mason Fidino is a quantitative ecologist at the Urban Wildlife Institute in Chicago. He says many animals are “synanthropic misanthropes,” meaning they love the city, but hate the people. Many wildlife species do their best to take advantage of all that the urban environment has to offer while avoiding interaction with humans as much as possible. A city park or wooded recreation area are potentially ideal habitats for many mammal species, but Fidino says that if humans and animals are using it at the same time, wildlife will be forced out. 

“There’s only certain species that are going to have the ability to actually modify when they are becoming most active,” Fidino says. “I’m just steadily more and more surprised to see how adaptable some species have become.”

‘HOW DO WE LEVERAGE WHAT WE HAVE IN A CITY?’

One way to reduce the detrimental impacts that cities may have on wildlife species could be to provide more ample greenspace within urban areas. Ensuring cities have adequate greenspace has enormous benefits for people as well as wildlife. Green areas within cities have been shown to improve human health and mental well-being, reduce temperatures in areas that are otherwise over-stocked with heat-absorbing concrete, and provide cleaner air. Wildlife benefits from connectivity, and providing ample greenspace within cities may better intertwine urban animals with nature and lessen the impact of urban sprawl. Scientists are still trying to understand how much greenspace is necessary for humans and wildlife to better co-exist in cities. Implementation of large expanses of greenspace within cities could ultimately increase the overall urban footprint on the natural environment, creating increased sprawl and commute times for humans. Researchers like Fidino are currently working to answer, “How do we leverage what we have in a city? And how can we modify what’s already present within the city in order to make it better for wildlife?”

As mammals become more adapted to urban living and using cities and suburbs, will that increase the number of negative encounters between people and wildlife? Not necessarily. Experts agree that the root cause of human-wildlife conflict in cities often comes down to people doing things they shouldn’t be doing. Whether it’s feeding wild animals, not sealing garbage or feeding pets outside, education, they say, is the key to co-existence, especially in a city like Missoula. 

“We really beat the drum here. We try to, anyway,” Jonkel says. “This is Missoula, this is wild country, govern yourself accordingly. People just have to be smart.” 

Missoula is just one example of a city that is rapidly expanding into the wild habitat that surrounds it. Over the course of his dissertation work, Hansen set cameras in more than 1,000 different locations, and they were triggered by black bears 570 times. As he took a close look at their activity patterns he noticed they are using wild and urban areas at about the same rate, only at different times of day. After collecting and analyzing the data, Hansen reflected on his findings. 

“It’s cool to think that even though we are seeing strong effects of urbanization on wildlife, that there’s still a ton of wildlife around and they still use a lot of the area that we inhabit.”

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