Cities provide us with many benefits: better educational and employment opportunities, exposure to more diversity and multicultural influences, improved infrastructure and access to public transportation. On the other hand, urbanization and the consequent changes in land use often result in air, land and water pollution; economic inequalities; an increase in health issues; and overcrowding.
In some cases, such land use changes can amplify—or, conversely, mitigate—the impacts of climate change. For example, one research study found that expanding urbanization, along with much hotter and drier conditions in Los Angeles, has driven declines in more than one-third of the bird species in the region. Still, other species of birds have been able to not only survive but thrive.
In the Midwest, urbanization is causing a different kind of threat to animals. In Chicago, coyotes that live in the most-developed areas of the city were found to have higher cortisol levels—a proxy for chronic stress—than animals living in suburban or natural areas.
So, is rapid urbanization harming most of our kin in the animal kingdom, or will we all find ways to adapt?
Birds: windfalls and double whammies
Today, California’s birds are facing a range of challenges. Over the course of the 20th century, agricultural development and urban sprawl have dramatically changed the landscape of the state, forcing many native species to adapt to new and unfamiliar habitats. In fact, urbanization and much hotter and drier conditions in L.A. due to human-caused climate change have caused declines in more than a third of bird species there. Meanwhile, agricultural development and a warmer and slightly wetter climate in the Central Valley have had more mixed impacts on biodiversity.
Usually when scientists want to study the impact of climate change on biodiversity, they only model the effects of the climate without considering the effects of land use. But what we’re now learning is that different kinds of birds have varied responses to these changes, complicating forecasts of extinction risk.
In a new study that was published in the journal Science Advances in February 2023, biologists at the University of California, Berkeley, used current and historical bird surveys to reveal how land use changes have amplified—and in some cases mitigated—the impacts of climate change on bird populations in Los Angeles and the Central Valley.
In an effort to revisit and document birds and small mammals at sites first surveyed a century ago by UC Berkeley professor Joseph Grinnell, university researchers resurveyed birds at 71 sites in the two locations. They then used their findings—along with current and historical data on land use, average temperature and rainfall—to analyze how shifts in the climate and landscape may have contributed to changes in bird populations.
Grinnell was a teenager when he first started documenting birds in the late 1890s near his childhood home of Pasadena, California. He later perfected his detailed approach to surveying as a professor of zoology at UC Berkeley and as the first director of the campus’s Museum of Vertebrate Zoology. Without the advanced binoculars and recordings of bird calls that we have today, Grinnell had to learn about birds through the resources that were available then, such as handbooks, popular guides or specimens in museums.
Grinnell’s meticulous field notes allowed the Berkeley researchers to construct a historical baseline of California’s birdlife at the turn of the 20th century. His notes were so detailed that current researchers were able to reconstruct the birds encountered each day in the past and account for the ways that new technologies have made it easier for contemporary biologists to detect birds. This analysis allowed the scientists to make direct comparisons between current and historical bird surveys.
To tease apart the disparate and sometimes opposing impacts of climate change and land use change, the researchers analyzed historical maps of agricultural areas and urban development to determine how the landscape at each study site had been modified during the 20th century. They also obtained historical average temperatures and rainfall at each site.
In L.A., they found that 40% of bird species were present at fewer sites today than they were 100 years ago, while only 10% were present at more sites. For example, the American crow and Anna’s hummingbird were able to adapt to both hotter and drier conditions and to urban development, experiencing what the researchers call a population “windfall.” Other birds, such as the western meadowlark and the lark sparrow, were negatively impacted by both changes, instead suffering a “double whammy.” Species that are undergoing mixed impacts included black phoebes, blue-gray gnatcatchers, great egrets and house wrens.
Meanwhile, in the Central Valley, the proportion of species that experienced a decline (23%) only slightly outnumbered the proportion that increased (16%). In many cases, there were opposing responses to climate and land use changes by bird species; where a climate threat might cause one type of bird to increase while a land use threat caused that same bird’s numbers to decline, moderating the impacts of each threat alone.
The species that have been able to persist under agricultural changes or even colonize and increase because of those changes tend to be species that are more common and widespread, while the birds that started disappearing when the natural grasslands were replaced by agriculture were usually the more sensitive ones. In urban areas, however, there are fewer species that can avoid city hazards and find what they need.
The scientists say that their findings highlight the fact that climate change and land use change happening at the same time creates happy conditions for some species, while others—pushed and pulled in different directions—find themselves struggling.
Coyotes: cars and copious cortisol
Coyotes have been infiltrating our cities for decades. Although cars are the biggest threat to these wild canines that are now are our fellow residents, a new study suggests that urban living poses a different kind of hazard to coyote health: one in the form of chronic stress.
Recently, researchers from The Ohio State University examined the concentration of the stress hormone cortisol in the hair of almost 100 coyotes living in the Chicago Metropolitan Area. Results, published online recently in the journal Science of the Total Environment, showed that coyotes that lived in the most-developed areas had higher levels of cortisol—a hormone produced as part of the body’s response to stress—than animals living in suburban or natural areas.
Two other factors stood out for their association to higher stress: poor body condition, mostly related to sickness with the skin disease mange; and being either a loner or an alpha in a pack, the males and females that constitute breeding pairs. Whether the stress linked to these factors can be traced directly to urban living or is just part of coyote life remains a bit of a mystery.
For this study, the scientists shaved a bit of hair from the rump just above the tail of 97 coyotes. Most of them were alive, but some were captured after death from illness or being hit by a car. The animals were also outfitted with radio-tracking devices that enabled researchers to monitor their space use and determine their social status. Data collection occurred between 2014 and 2018.
The hair samples were analyzed for their concentration of cortisol. Analyzing hair, as opposed to blood, provided an estimate of long-term stress over the previous weeks or months before collection rather than a reaction to an immediate stressor. Statistical modeling then revealed the factors that were associated with higher stress.
The researchers predicted that coyotes living in the more developed areas of Chicago would have higher concentrations of cortisol than coyotes whose packs had more flexibility of movement and less exposure to people in the less dense areas in which they lived. The results bore out that hypothesis, but the findings also showed that there is more to the story of modern coyote life: poor physical condition is linked to higher stress, which poses a chicken-and-egg question of which problem came first. Sarcoptic mange infection itself doesn’t kill coyotes, but the loss of hair makes them susceptible to succumbing to cold Chicago winters.
In addition, the analysis suggested that the responsibility of running a pack or living outside a pack is stressful. Alphas are responsible for territorial defense, and they’re the only ones that are breeding. That was reflected in the cortisol levels. Transients, on the other hand—adult coyotes that have left their parents but not yet established or joined a pack—have a different set of worries. While they don’t have to defend a territory, they do have to avoid getting attacked by pack-member coyotes. They need to travel through other coyotes’ territories on a constant basis, and at the same time try to avoid cars and people. In 2014, it was reported that some coyotes in Chicago had learned to look both ways before crossing a street, a finding that speaks to both their frequent exposure to risks that threaten their survival and their ability to deftly adapt to hostilities in their environment.
Coyotes are the first mammalian carnivore that has been evaluated for stress in an urban environment. Studies such as this one help us understand how well animals are adjusting to our cities—or not. And with coyotes, it turns out, it’s complicated.
Climate change: community collapse and tiny triumphs
The significant decline in bird species in L.A. over the past century is similar to the shocking bird community collapse over the past 100 years in the Mojave Desert that was linked to heat stress from climate change. Most of the L.A. birds ended up in the “loss” category. California’s Central Valley had less change, in general, and there were losers as well as some winners.
Coyotes, too, are losing and winning. While The Ohio State University study showed plenty of individual variations in stress levels of the animals even in the highest-stress groups, coyotes overall seem to be adjusting to urbanization quite well; their survival rates are high, and their food supply is ample. So, while the city does present challenges for them, coyotes are demonstrating that they’re extremely good at what they do.
Let’s hope that we’re equally adept at making sure that despite the losses we help inflict on the “others” that share this planet, the wins we’re able to help them achieve edge out.
Here’s to finding your true places and natural habitats,