Climate Change in Microcosm
Research in a state wildlife area is revealing how wild animals are struggling with and adapting to an environment in flux
Jon Pauli is perched in the passenger seat of a mud-spattered Ford F-250. His ceramic mug brims with coffee as graduate student Evan Wilson guides the truck, loaded with equipment, over the rough roads of the Sandhill Wildlife Area. A spill is just one big jostle away, but Pauli prefers things this way — a sign of his coffee devotion. He jokes about how his wife once tortured him for weeks when she unknowingly bought decaffeinated beans.
But Pauli’s love for coffee seems lukewarm compared to his passion for his work as an associate professor of forest and wildlife ecology. He radiates enthusiasm — along with an abundance of laughter and a smattering of swear words — as he expounds upon conservation biology, Sandhill, and the research his lab is pursuing.
He shares his passion with two other forest and wildlife ecology professors: Ben Zuckerberg and Zach Peery. Their collective work explores one question: How do we protect species that are vulnerable to disruptions in their environment, such as climate change and land use? The three have formed a productive collaboration and, it seems, an easy camaraderie. It’s not hard to imagine them walking into a pub together and leaving with a plan for their next great endeavor.
And Sandhill Wildlife Area, 9,000 fenced-in acres of state land set aside for research and hunting, is a perfect place for them to pursue their ideas. Situated just off a rural highway in westcentral Wisconsin, the area is a bit unassuming at first, with an office and a dormitory next to a small paved parking lot. But once inside the fence, it’s clear the area holds a diverse wealth of landscapes, plants, and animals.
Sandhill was named for the sandy ridges that roll gently across the property. Animals are abundant. On a quick ride through its marshes, flowages, and forests, one can glimpse swans and songbirds, ducks and deer. A closer look might reveal turtles, grouse, and porcupines, the animals at the center of Peery’s, Zuckerberg’s, and Pauli’s work.
Rarely seen is the small herd of American bison that has called Sandhill home since Wallace Grange owned the land. Grange and his wife, Hazel, purchased Sandhill in the 1930s and spent more than two decades nurturing the land and running the area as a game farm. Upon his retirement in 1962, Grange sold the area to the state of Wisconsin, requiring that it be used as an education and demonstration area. Today it is managed by a team of Wisconsin Department of Natural Resources (DNR) biologists, technicians, foresters, and wildlife researchers.
An ideal setting for research, Sandhill offers years of data for scientists like Pauli, Zuckerberg, and Peery. Lloyd Keith, a retired forest and wildlife ecology faculty member, was studying the area’s animals and weather conditions as early as the 1960s.
“We have long-term data on what this place used to look like, and we have data on what it looks like now,” says Pauli. “It’s not just the place that makes Sandhill special, it’s all of the data we are drawing upon. Long-term field sites like this are pretty rare. They’re really important to be able to understand ecological change.”
WITH YEARS OF ACCUMULATED data in hand, Pauli and Wilson are working to understand the relationship between climate change, snowshoe hares, carnivores, and porcupines (especially porcupettes, the delightful but rarely heard name for baby porcupines). Their project is, in essence, a time machine. They have pushed the Sandhill Wildlife Area back in time by reintroducing an animal that is no longer naturally present within its boundaries: snowshoe hares. By doing so, they can observe how the species, which evolved to survive snowy winters, is adapting to warmer winters and dwindling snow cover. Further, they can better understand how the effects ripple out into populations of other animals, such as porcupettes.
Sandhill is right at the edge of snowshoe hare habitat. As with many animals, hare populations go through rise-and-fall cycles, and these cycles have been associated with patterns in predator–prey relationships. Over the last 50 years or so, through multiple cycles, snowshoe hare numbers in Sandhill steadily decreased as the animals moved north. Eventually, they functionally disappeared from the area.
To study what happens to the hares with shorter winters and less snow, Wilson and Pauli had to reintroduce them. This involved a slow, laborious process of catching hares from other parts of the state and releasing them at Sandhill.
“We trapped hares north of here using baited traps put out at night,” Wilson says. “The next morning, we’d come back and collect the hares — usually two or three per night. After about a month and a half of trapping, we brought the hares down here, radio-tagged them, and did a kind of soft release.”
A soft release entails building an enclosure for the hares so they can acclimate to the area. The kennel-like structures provided food and shelter for two nights before the hares were fully released. Wilson eventually released 99 hares into Sandhill, just under his goal of 100. “Close enough,” he jokes.
The hares were released in winter, when their seasonally changing coats matched the white snow cover. A late-winter snow melt offered a true test of the team’s hypothesis. Researchers had proposed that early snow melt and less snow cover would lead to more hares being predated because they would be easier to spot against the now-brown background. And that’s just what they found. During the first week of an early snow melt in March, 30 percent of the hares died. In comparison, in weeks when hares matched the surrounding snow, an average of 7 percent of the hares died.
“Not all the weeks were that extreme, but weekly survival is a short interval to be able to measure,” says Wilson. “If you’re experiencing enough mortality in a week for that to be an important number, that’s telling.”
It was experimental data to back up what Pauli and his colleagues had been hypothesizing for some time — shorter winters are directly related to the survival of snowshoe hares. But if snow is melting earlier, why don’t the hares’ coats just turn to brown earlier?
“Molting is predominantly driven by solar cycles,” explains Pauli. “They’re cueing into photoperiod [day length] to change from white to brown. But snow isn’t cued in on photoperiod. Snow is melting earlier and earlier in these areas, and we’re seeing a mismatch of white animals on brown backgrounds. That’s why this is a climate change story.”
As warmer winters hit areas where snowshoe hares live and the hares’ predation rates go up, other animals in the ecosystem will feel the effects as well. With fewer hares to eat, predators such as fishers and coyotes will turn to other possible prey, such as porcupettes, likely causing their numbers to decline as well. To better understand these relationships, Pauli and Wilson are currently investigating what killed the hares (using DNA found on the hares and prints found nearby) and monitoring porcupette populations in Sandhill. It’s likely that the ripple effects of losing hares will be felt widely in areas of warming winters.
So what can be done? That’s another question that Pauli and Wilson are working to answer. And they have some suggestions. They have found that patches of high-quality, dense habitat are important for hares to survive. Historical data suggest the same — some of the last areas where Keith, their predecessor, recorded hares were large patches of aspens, alders, and low-lying conifers.
“These areas are ideal,” Wilson says. “They give the hares hiding spots, thermal cover, and food resources all in one spot. Animals that have those areas available to them had higher survival.”
Having a possible solution or recommendation to at least slow the decline of hare populations is exciting for Pauli. “When we talk about climate change, land managers aren’t always offered tools to manage it,” he says. “But Evan’s work shows that there may be habitat management techniques that people could employ to buffer the effects of climate change and promote species like snowshoe hares. We’re not just telling you bad news; we’re also trying to provide you with tools to promote this species on the landscape if that’s what you want to do.”
As Wilson’s time in the field came to an end in summer 2018, he continued to tease out the different aspects of his work and create a clearer picture of what he found at Sandhill. That picture will help other researchers and may guide land managers looking for ways to mitigate the effects of climate change on different species.
A WARMING CLIMATE ALSO POSES challenges to the ruffed grouse. It’s possible the thick-feathered, brown and gray game birds could benefit from some of the same habitat management concepts that Wilson and Pauli suggest. Like snowshoe hares, ruffed grouse have adapted to cold winters and snow cover, and they have undergone extensive study in the Sandhill area historically. Ben Zuckerberg and graduate student Amy Shipley want to understand how changing winters might affect the birds.
Zuckerberg has been modeling changes in grouse populations (which experience cycles much like those of snowshoe hares) for several years, and Shipley came onboard to investigate the mechanism of those population trends. Sandhill was, again, the ideal place to study what the birds were doing during winter and how they might respond to less snow.
“Ruffed grouse is a really interesting indicator species,” Zuckerberg explains. “They get through the winter, but it’s definitely a bottleneck in terms of their populations. Populations have been declining, especially those around the southern boundary of their range. Sandhill is at that boundary.”
Like snowshoe hares, ruffed grouse are vulnerable to the loss of snow cover. They burrow under snow in winter to keep warm and, it is surmised, to avoid predators. Scientists have documented a 7–10 percent loss of snow cover per decade in areas of the Upper Midwest, which means that this important refuge is disappearing. Not surprisingly, a DNR report on grouse at Sandhill found that winters with low amounts of snow meant fewer birds the following spring.
To better understand why, Shipley undertook a project to track grouse with radio transmitters through three winter seasons. She tagged about 20 birds each year, hoping they would reveal which roost sites grouse were using at Sandhill and how their behavior and survival rates were responding to less snow cover.
Shipley looked closely at physiological stress in Sandhill’s grouse. Chronic stress in the winter can lead to reproduction declines the next season — an indicator of poor fitness. Shipley collected samples of droppings from which she measured levels of the stress hormone corticosterone.
“We found a strong relationship between stress and temperature,” she says. “The colder it was outside, the more stressed the grouse were because it takes more energy to keep warm. When the birds were able to burrow in the snow, though, that relationship went away. Birds that were in snow burrows were a lot less stressed.”
Because snow cover is so important to grouse, managing habitat in a way that maintains snow cover could go a long way in protecting them and encouraging populations of grouse in areas where numbers are declining. For instance, grouse sometimes roost under low branches of spruce trees and under the cover of fallen trees. Conifers and complex understories in forests can also maintain snow and provide warmer areas for the birds. As Shipley continues her work, she plans to identify more strategies to optimize grouse roosting and survival. It’s a similar story to what Pauli and Wilson see with hares.
“Grouse are an important sentinel of climate change, in particular the loss of snow cover throughout the Upper Midwest,” Zuckerberg says. “We need to think about whether there are aspects of habitat management that will allow animals to continue to use their adaptations to snow cover to survive.”
HABITAT MANAGEMENT MAY BE ONE way to protect another vulnerable animal — the turtle. Turtles are one of the most endangered groups of reptiles. Zach Peery and graduate student Nathan Byer are trying to understand how environmental changes are affecting three freshwater turtle species in Wisconsin: Blanding’s turtles, snapping turtles, and painted turtles. Blanding’s turtles are globally endangered, and snapping and painted turtles, while more common, are also declining in locales throughout their North American range.
For more than 20 years, Wisconsin DNR wildlife biologist Dick Thiel captured, marked, and released turtles at Sandhill. He accumulated a large data set, and Peery and Byer are contributing to it by radio-tracking turtles. They’re also using the historical information to study what happens to turtle populations in response to environmental disturbances. It’s an ideal site, then, for evaluating early warning signs and long-term impacts of climate change on turtle populations.
“The long lives of turtles make them very sensitive to environmental change, particularly if those changes reduce adult survival,” explains Byer. “So most of our research focuses on integrating local studies and statewide monitoring to predict responses of Wisconsin turtles to climate and land use changes.”
On a cloudy fall day, Byer sets out on a gravel road at Sandhill to release a Blanding’s turtle riding in the back of his SUV. Easily identified by its yellow chin and throat and the pale speckles on its upper shell, the Blanding’s turtle is docile and semi-aquatic. Driving just behind the bison enclosure, Byer points down at the road and says that in spring this is a popular nesting site for the turtles. It’s hard to imagine the gravel and dirt being a suitable area to dig a nest, but he says they find spots where the material is loose.
Blanding’s turtles are interesting animals to study for several reasons. They are long-lived, sometimes reaching up to 70 or 80 years, and they don’t reproduce until around age 15 or 16. When they do reproduce, they practice “natal philopatry” — that is, they return to where they were born to nest. Also, females lay their eggs and leave. They have no knowledge of the fate of their offspring or how well the nest fared.
“We’ve found in our work that there is a friction between what’s good for the mother when nesting and what’s good for the offspring,” says Byer. “Because this is a long-lived species, it’s usually better for the mothers to be selfish. For instance, they tend to nest in areas close to woods. This may not help the nests survive, but it does seem to reduce the risk of predation for the mothers. And because they’re cold-blooded, they are often more interested in maintaining a comfortable body temperature than picking an optimal nesting site.”
By studying nesting sites and turtle numbers in Sandhill, Byer is continuing work started by a former graduate student in Peery’s lab, Brendan Reid PhD’15. The goal is to determine what factors are influencing population size, age, and distribution in the area. There are a number of suspects, many of which are related to changing climate and how humans make use of the land.
“After turtles spend the winter underwater, the males set out to find females to mate with. During that time, they’re hopping between wetlands,” explains Byer. “Changes in climate could cause some of those wetlands to dry up and disappear, and land use change can affect the distribution of wetlands. Both make it harder for turtles to move between populations.”
Land use poses other problems for turtles. Reid’s genetic work shows that agricultural lands form barriers for turtles, stopping them from dispersing and mixing with other populations, and that urbanization reduces the number of wetlands and nesting areas they need to survive. As roads are built through turtle habitats, females have to travel farther and through more populated areas to find suitable nesting sites. This puts them at higher risk for death from predators and automobiles. As evidence of this, Reid’s research has found sex ratios skewed toward males and low genetic diversity in areas with many roads.
Warming temperatures also threaten turtle populations. Turtles have temperature-dependent sex determination — the temperature of the eggs during a particular point in development dictates the sex of the offspring. The difference of just a degree or two can flip the switch. With warmer temperatures, more females will be born, skewing sex ratios, reducing population growth rates, and contributing to the loss of genetic variation.
“They may find ways to change their nesting behaviors to account for temperature changes,” says Byer. “They could start nesting earlier in the season or nest under more cover so the nests are cooler. But that may be a trade-off for the mother if it puts her more at risk. There is a lot of uncertainty regarding how, say, nesting in a more shaded area may have indirect effects on the nesting turtle.”
Habitat management could solve some of the problems freshwater turtles face in Wisconsin. Efforts to protect wetland areas could reduce the distances turtles need to travel during mating season. Land managers could provide nesting turtles with areas of loose dirt and gravel far from roads and close to woods. Despite the many threats Blanding’s turtles face, work from Peery’s lab suggests that the Sandhill population is increasing in response to nesting and wetland habitat restoration.
“DNR employees have been restoring prairie and oak savannah at Sandhill since the 1990s. We have discovered that these areas are good for nesting Blanding’s turtles,” says Byer. “We are seeing more young turtles returning to recently restored habitats, indicating that hatchlings from those areas are surviving to adulthood.”
In addition to tracking the turtles, Byer is taking samples of their blood for a genetic study. He plans to compare their genetic makeup with that of turtles in other areas of the state. If genetic differences are related to climate conditions, this could be evidence of adaptation to climate change.
“We are incorporating information from both long-term nesting and population monitoring efforts at Sandhill with more recent statewide genetic sampling to develop sound conservation strategies,” explains Byer. “Integrating multiple data sources is important for accurate predictions in an uncertain future.”
THE UNKNOWNS ASSOCIATED WITH environmental change and the randomness of fieldwork both present many challenges for research at Sandhill. But addressing those challenges can be rewarding for wildlife ecologists. Jon Pauli, still precariously balancing his coffee mug in the passenger seat of the jostling truck as the tour of Sandhill comes to an end, explains why. It seems that unpredictability — a characteristic that defines the animals he studies, the landscapes they live in, and even the research process itself — is one of the things he loves.
“We work in places where you’re constantly dealing with problems and proven wrong,” says Pauli with a laugh. “You start to embrace the things you can’t control, and you start to accept that you need those things to answer your questions. I mean, I didn’t know it was going to freaking snow in April here this year. But that helped us understand our work and the animals even more.”This article was posted in Changing Climate, Fall 2018, Features, Healthy Ecosystems and tagged Amy Shipley, Ben Zuckerberg, Blanding’s turtles, Brendan Reid, climate change, Dick Thiel, Evan Wilson, Forest and Wildlife Ecology, Jon Pauli, Lloyd Keith, Nathan Byer, painted turtles, porcupettes, porcupines, ruffed grouse, Sandhill Wildlife Area, snapping turtles, snowshoe hares, Wallace and Hazel Grange, Zach Peery.