These Animals Are Already Adapting to a Changing Climate

A warming world is forcing wildlife to adjust in unexpected ways

By Sofia Quaglia

August 17, 2023

A yellow-bellied marmot coming out of their burrow.

A yellow-bellied marmot. | Photo by Wallace Keck/NPS

Climate change is one of the top five drivers of extinction, but it’s not always a zero-sum game. In general, scientists expect species will have to move upward in elevation or latitude to cope in a warming world. However, in California, many animals have been adapting to their mutating environments in ingenious ways. They’re prioritizing environmental preferences other than temperature, they’re switching their diets, they’re altering their genetic makeup, and they’re changing their reproductive behaviors. 

Scientists still cannot tell if these adaptations, no matter how impressive, will be enough to help animals weather the impacts of climate change successfully. Solving this mystery is at the heart of research that might help conservationists save species from vanishing. Here are four groups of animals that experts say are already evolving to meet climate change head on. 

Sierra squirrels are sticking to favored environments

Since many squirrel species living in California’s high-elevation Sierra Nevada are already as high as they can go, it was unclear whether they’d be able to handle the heat. But when researchers carried out an in-depth study analyzing data from over 6,000 observations of yellow-bellied marmots, Belding’s ground squirrels, and golden-mantled ground squirrels, they found that some were doing just fine.

Their observations suggest that there are other crucial factors—such as topography, like steepness and landcover—that define what makes a suitable home for these mammals. For instance, yellow-bellied marmots and the Belding’s ground squirrel like to hang out in grassland meadows. But within that same environment, Belding’s ground squirrels prioritize wet vegetation the most, while marmots prefer drier conditions. Golden-manteled ground squirrels like more snow-free days and more trees, both of which are expected to be consequences of increasing heat in higher elevations.

Temperature isn’t the only element at play. “The current drivers of where species live in the world are different for each … so as the world changes, how species respond or if they can respond is going to be different too,” Aviva Rossi, the study’s author and a wildlife ecology professor at the University of San Francisco, said. Pinning these nuances down is what’s going to help us better understand what might happen as the world changes. 

California’s sea lions have switched up their diet 

The California sea lion is also somewhat of a paradox, according to May 2023 research in Current Biology. Since the 1970s, regardless of the warming temperatures and changing sea levels, the number of breeding females has more than tripled—going from 50,000 to almost 170,000.

Researchers compared data from museum specimens from central and northern California from 1962 to 2008. The results suggest these animals have avoided fierce competition and starvation by diversifying their diets and venturing farther out into the ocean, and up the coast, to areas where they’d never gone in the past. They’ve been seen as far up as Alaska. 

“Flexibility has been really important for them to overcome prey changes because of climate change,” Ana Valenzuela-Toro, the author of the study and researcher at the University of California, Santa Cruz, said. “I tend to think of California sea lions as the raccoons of the sea.” Male sea lions also amped up their neck flexibility and biting force over time, again supposedly to feed on a broader range of prey.

Sticklebacks have changed their looks 

Over the past 40 years, a small colorful fish called the three-spined stickleback evolved to live in drier, warmer habitats, according to 2019 research published in Global Change Biology. In northern California, three-spined sticklebacks live in rivers and open waters, so they’re more exposed to predators and have evolved bony plates along their sides to protect themselves. Fish from the south of California tended to have less of these lateral plates because they live in more pondlike environments where they can take refuge in vegetation.

Now that the climate is making other areas warmer and drier, more California estuaries are getting shallow and pondlike, and the three-spined stickleback from central and northern California are increasingly looking like those in the south—they’re losing their armor.

This is yet another example of how it is not just the heat or the changing precipitation from climate change that is altering these animals’ lifestyles—it’s how climate has changed the structure of their habitat. “It’s like this mosaic of different causes and consequences,” Eric Palkovacs, the study’s author and a professor of ecology and evolutionary biology at the University of California, Santa Cruz, said. “The point at which you see the low-plated phenotype being 100 percent of the population has moved northward.” 

West Coast birds have changed their nesting times

As springs and summers get warmer and the weather gets more unpredictable, 202 species of West Coast birds—including tree swallows, eastern bluebirds, pileated woodpeckers, and Calliope hummingbirds—now nest five to 12 days earlier than they did 70 to 100 years ago, according to 2017 research published in Proceedings of the National Academy of Sciences

This is probably a trick birds pull off to try to avoid nesting during times of the year that could be too warm for fragile eggs or high-maintenance chicks to survive, falling victim to overheating, according to study author Jacob Socolar, an ecologist who was working at the University of Connecticut at the time. In fact, it spares them 2°F in heat that they would have otherwise encountered if they hadn’t shifted their timing. 

“[During nesting] they're dealing with, by far, the most severe energetic requirements that they're going to face. They're eating for two or four or five,” Socolar said. “In mountain systems in particular, there's good reason to imagine that once the young fledged and a heat wave hits, they can all go up the mountain easily.” 

Will these adaptations be enough?

The issue is that tweaks and adaptations, no matter how big, can probably only serve these species so much. The Sierra squirrels might have other factors they prefer above temperature when it comes to picking a home they can thrive in, but that’s a double-edged sword. If they get too picky, species with a narrower niche have a narrower geographic range and will still be more vulnerable to climate change.

For California sea lions, adaptation happened at a moment when their preferred prey—sardines and anchovies—were abundant and rich in the oceans. There was room for them to make changes in their diets. Data now shows these fish populations are collapsing, and it’s unclear whether sea lions will be able to change their diets once again. 

“They have been able to overcome the challenges associated with climate change so far, but there is a point when that will not be possible to achieve anymore,” Valenzuela-Toro said. “We have started unraveling what that threshold is for California sea lions. Now we realize that probably they are very vulnerable for future scenarios.”

And as increasingly more stickleback populations become completely dominated by armorless fish, there could be a time when the genes for those lateral plates completely disappear. That leaves the species vulnerable if habitats or predators change once again because natural selection for armored fish will not be possible without any genetic variation within populations. And since populations are way less interconnected than they historically have been, it’s harder to move adaptive genes across the landscape, Palcovacks said. 

The issue with birds anticipating their nesting times, too, is that it’s unclear whether this actually makes much of a difference in survival rates. “Something that still seems to really matter is those late summer temperatures,” Socolar said, so changing nesting times isn’t enough. “They're doing the best they can, but it's not the case that everything's hunky dory for these birds because they've managed to start nesting earlier.” 

Research projects like these highlight how, moving forward, conservation strategists need to keep a wide range of factors in mind at all times—and each of these might be radically different for each species, in a way that is less clean cut than just “winners and losers” of climate change. 

“Really, it's going to be on a spectrum of responses,” Rossi said. “We all want a very clean story about whether things will be OK or not. But there are so many factors even within a single species that it's very difficult. The response to climate change is going to be very complex.”