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Warming temperatures make life even tougher for urban wildlife

U researchers provide trail-camera data for the Utah portion of a national study of city-dwelling native mammals.

Human-driven climate change could worsen the effects of urbanization on native wildlife, suggests new research based on analyses of data recorded by 725  trail cameras set up in and around 20 North America cities, including Utah’s urban areas along the Wasatch Front.

The main finding was that urbanization’s negative effects on wildlife are tougher on larger-bodied animals and are worse in the less vegetated cities in drier regions, such as Phoenix and Salt Lake City, according to University of Utah wildlife biologist Austin Green, one of the study’s many coauthors.

A nonnative feline saunters past two mule deer in this image recorded in 2019 in South Salt Lake’s General Holm Park. Credit: Austin Green

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“Those cities that don’t have as much rainfall have higher average temperatures, the effects that they had on wildlife were greater than in cooler and wetter cities,” Green said.

These findings are based on thousands of photos of wild animals, namely 37 species of native mammals that live in or near cities, ranging from squirrels to black bears. The images were recorded by motion-triggered camera traps operating in the summer of 2019 in places used for outdoor recreation within cities and up to two kilometers beyond the urbanized boundary. To ensure privacy, images of people were automatically deleted by the program that uploaded the photos, according to Green.

Led by Arizona State University biologist Jeffrey Haight, the study published Monday in the journal Nature Ecology & Evolution.

Haight and collaborators from around the country analyzed data from 725 camera traps to assess the composition of native mammal communities and the relative occupancy of each species. In partnership with the Urban Wildlife Information Network, the team covered Salt Lake City, Chicago, Los Angeles, San Francisco Bay Area, Atlanta and Austin and Edmonton in Canada and 13 other cities in the course of some 20,000 camera days.

Camera traps open new window into lives of animals

The researchers found that species occupancy and diversity were most negatively related to urbanization in warmer and less-vegetated cities. Sanford, Fla., for example, which has more green vegetation than other cities with a similar temperature, supported a more diverse mammal community than hot arid Phoenix, where the surrounding landscape harbors far less vegetation. In general, there was lower species diversity in more-urbanized areas of a city—the parts with highest percentage of impervious surface cover—and in more-urbanized cities.

A deer recorded by a trap camera in the Wasatch foothills. Credit: Austin Green, University of Utah.

“That kind of insinuates that if the climate is going to continue to get warmer and rain events are going to continue to become more dispersed across time, then wildlife are going to have a harder and harder time adapting to urbanization,” Green said.

He attributed that conclusion in part to the “heat island” effect of urbanized areas, where paved landscapes absorb heat in the day, then release that heat during the night.

Role of citizen science in wildlife research

“The vast majority of animals living in urban areas utilize that nighttime period specifically to avoid humans, but also to have a bit of a temperature refugia,” he continued Green, whose U faculty mentor Cagan Sekercioglu is a co-author. “They stay pretty sedentary during the day, the hottest time of day, and then they use the coolest part, which tends to be at night to actually move around. So if that part of the day is continuously getting hotter and hotter, then they’re not able to get the resources they need.”

Contributing to the study was Utah nonprofit Sageland Collaborative, which helped Green launched a citizen science campaign known as Wasatch Wildlife Watch. Since 2018, has set up 1,500 camera sites and generated massive amounts of data that were the subject of Green’s graduate studies.

Austin Green rigs a trail camera in Red Butte Canyon, just east of the University of Utah campus.


He completed his doctorate in biology last year and is now a postdoctoral researcher with the College of Science’s Science Research Initiative.

The Utah data used in the new study was taken from 55 sites, including Salt Lake City Cemetery, Tanner Park, the Miller Bird Refuge and Jordan River Parkway.

“The vast majority of the cameras were set up in recreational spaces, typically city parks or protected areas,” Green said. “Within those parks, they’re typically concentrated in areas where we can have high likelihood of detecting wildlife activity, such as wildlife trails, hiking trails, low-use roads, water sources.”

Amassing data about various species of wildlife in a diverse group of cities enabled the researchers to draw strong conclusions that could help urban planners to better accommodate wild animals.

“The biggest take home is that we should be cognizant about the way we design cities or the way that we restore natural areas to cities,” Green said. The study affirms the wildlife benefits of maintaining larger vegetated areas within cities, as opposed to the network of yards that typify suburban sprawl.

A copy of the study, titled “Urbanization, climate and species traits shape mammal communities from local to continental scales,” and photos are available upon request. Funding came from the National Science Foundation, along with the Abra Prentice-Wilkin and the EJK foundations.