Tag: Ecology

Wildlife populations are dynamic—ever-changing, depending on circumstances. They increase when resources are abundant and decrease when resources dwindle. Populations are limited by numerous factors that affect their ability to survive and reproduce. Factors, like predation or disease, that limit high-density populations more readily, as well as more sweeping large-scale factors, like habitat change or loss.

However, limiting factors are also wide-ranging and often entangled with each other—a giant web of factors where if you pull on one thread, others are sure to respond. This is where Taylor Ganz, Ph.D. candidate from the University for Washington, comes in. Taylor has been working for the last four years to understand how deer and elk populations in Washington have been changing as they respond to factors in their environment.

I met up with Taylor on a mostly sunny day for a hike in the Capitol State Forest near Olympia, WA to talk about her research and to learn more about population dynamics.

The Hike

• Trailhead: Mima Falls Trailhead, Olympia, Wa
• Distance: 6.5 miles
• Elevation Gain: 700+ feet
• Details: There is ample parking at the trailhead and a pit toilet. Trailhead is very accessible, but Discover Pass is required for parking. There are many options for trail routes through the area. The Mima falls Loop is part of Olympia’s Capitol State Forest.

For the Love of Science and the Outdoors.

As we started down the tree lined trail, Taylor told me a bit more about her background and research.

“I have always loved science and being outside,” said Taylor. So naturally, in college, she studied physics and mechanical engineering. “I thought I would work in alternative energy design and development,” she explained. 

The problem was instead of doing engineering internships, like her classmates, she found herself drawn toward jobs in outdoor recreation and education. “I was working as a wilderness ranger… a flyfishing guide… a rock-climbing instructor…” For 5 years she worked for NOLS (National Outdoor Leadership School) before deciding “to get back to science.”

She started out at the Yale School of Forestry where she studied air pollution in sensitive alpine environments (tinyurl.com/scienceofsnowmelt), before making her way to the University of Washington to work in the Laura Prugh Lab on wildlife ecology.

Predator-Prey

Now Taylor is deeply entrenched in her research at UW. Taylor’s research is part of a big collaborative project between the Washington Department of Fish and Wildlife and The University of Washington called the Washington Predator-Prey Project (www.predatorpreyproject.weebly.com).

Wolves returned to Washington state in 2008 with just one breeding pair documented. Now, the Washington Department of Fish and Wildlife reports there are at least 145 individual wolves in Washington. The Washington Predator-Prey project was mandated by the state legislature in 2016 with the goal to understand the impacts of the recolonization of the wolves.

Taylor’s part in the project is focused on how deer and elk populations are impacted by predators, like the recolonizing wolves, both directly, by killing them, and indirectly, by influencing their behaviors or other predators.

 “Predators can impact individual prey by killing and eating them,” said Taylor, “…this may or may not impact prey at the population level.” Prey might avoid certain areas or move about differently in the presence of a predators. For example, the presence of a predator may cause deer to spend more time hiding and less time feeding. Of course, this can also have an indirect impact on the deer population by limiting food availability or stressing the animals, which could also decrease deer survival.

Taylor works two 5,000 square-kilometers study sites—one in the more populated northeast part of the state and a second in the less populated north-central part (situated on the east slope of the North Cascades). The northeast site has four wolf packs, while the northcentral site only had only two until recently.

Large-Scale Change

Young trees stood at attention on both sides of the wi­de gravel trail as we walked along. You could still see the stumps from the last harvest and grass-lined the trail.

“I am also interest in large-scale changes in the environment, like fires and timber harvest,” Taylor told me. This is why Taylor suggested visiting an active timber harvest site for our hike.  Though her research sites are in the northeast and northcentral parts of Washington state, much of the sites contain active timber harvest as well.

Areas that have been harvested for timber have the potential to create good habitat and forage for deer and elk populations, at least for a few years. Harvesting timber opens the canopy so that sunlight can reach the ground, which can promote the growth of shrubs and herbs that deer and elk feed on. As the trees grow up, they can provide a place to rest and hide from predators.

Keeping Track of Deer

Eventually, we dropped down into a section of forest with taller, but still not mature trees.  Sword fern and Salal became the dominant understory and I was excited to see a few trilliums still in bloom. Enjoying the shaded trail, I asked Taylor to describe just how she goes about finding deer and tracking them.

“We need to track adult females and younger animals,” explained Taylor.  Males are largely ignored for her study as they are abundant enough to get the females pregnant. Instead, the focus is on capturing and collaring adult female deer and elk and their fawns and calves.

“Elk are primarily captured by aerial darting, and mule deer are mostly collared by aerial rocket netting,” said Taylor. But for white-tailed deer, she often uses ground darting and special traps, called clover traps, to lure deer and capture them. Taylor described them as large boxes with a tripwire that closes the door. Bait, like corn, hay, or something called “sweet feed” is used to attract the deer inside. And once captured, the transmitter sends a text to Taylor, so she knows to check the trap.

When Taylor arrives at the trap, she needs to add a GPS tracker to the deer—this is a priority. To do so the clover trap is flattened and laid down on its side, essentially creating a “deer sandwich.” Taylor is then able to apply an anesthetic before tagging the deer.

The other tool Taylor uses to capture adult deer sounds a bit like a fourth of July firework or something military—”suspended rocket net.” This contraption uses a net with weighted corners that launches during capture overhead an unsuspecting deer.  Bait is used to lure the deer into position below the net before it is launched. “It’s kind of like a bug in a spider web,” said Taylor.

Tough Captures

Later, Taylor told me about the challenges of trying to capture new animals. First, it takes a lot of detective work, looking for “pellet piles” and tracks.  Then the trap must be “appealing for the deer.” Taylor told me about a time her boyfriend and dad came with her into the field. She had them both dig a shallow ramp in the snow up to one of her traps to make it easier for a deer to enter.

“No, we need a really gentle entry,” she told them as they worked. 

From then on, the trap was referred to as “The Ruby Creek Country Club,” based on its luxury accommodations and location.

Technology Revolution

No matter the method, once captured, the adult deer is collared with a GPS tracker, measurements are taken, and blood and hair samples collected. Vital signs are monitored during the process to ensure no harm. If the vitals deteriorate, the deer will be released. Blood is especially important for tracking pregnancy.

In addition, they will often ultrasound the deer in the field as well. And if pregnant, implant what is called a VIT (Vaginal Implant Transmitter). The VIT talks to the deer’s collar, texting Taylor when the VIT has been expelled during birth. From there, Taylor and her team can often track down the new fawn and add an expandable collar that uses radio telemetry to “speak” to the mom’s collar.

Currently, Taylor has about 200 ungulate “on air.” Each spring they capturing between 30-40 newborn fawns and elk calves.

“Much of the technology is really recent,” said Taylor. In the past, radio telemetry was really the only option for tracking animals, which requires more time in the field with receivers and triangulating positions. Now, GPS collars allow you to know where the animal is every 4 hours, and you can see their positions from the comfort of your own home if you want.

Elk Tracking

Of course, every animal is tracked differently. For Elk, for example, a mix of strategies is used, like aerial telemetry, in addition to GPS collar. It is also helpful to consider the behaviors of the animals for tracking. For example, often elk will move large distances in one day. When this movement stops suddenly in late May, this could mean a calf was born.

On the Look Out

At this point, we had made a few turns on our loop and were getting close to Mima Falls, our designated hiking destination. The forest was still fairly shaded with younger trees which made for a cool walk.

As we hiked, Taylor and I kept a lookout for signs of wildlife, but so far had not seen much if anything. Of course, that does not necessarily mean there is nothing around. I often think about the wildlife that I do not see while I am out hiking. Could there be eyes watching us now as we walk through the forest?

Deer are also on the lookout for other wildlife, especially predators. Of course, they are much more capable of detecting the presence of others than us poor-sensing humans. Interestingly, what a deer detects seems to matter a lot—changing their behaviors in possibly meaningful ways.

Wolves, Cougar, and Bear, Oh My!

Taylor mentioned a study out of Yellowstone that showed that when cougars were around, elk tended to move out into the open, but when wolves were around, they tended to move into more densely wooded areas. This makes a lot of sense, as cougar are ambush predators—stalking their prey and going in for a quick kill. Better to be out in the open where a sneak attack is more difficult. While wolves are coursing predators—chasing their prey to exhaustion. Better to be well hidden where it is difficult to chase.

“We have collared wolves and cougar, as well,” Taylor told me, as part of the Washington Predator-Prey Project.  Using a movement modeling technique called a “step selection function,” Taylor is also looking at how deer and elk are responding to predators. 

“Basically, the model considers a handful of possible routes a deer or elk might take, based on their location at a given time, and compares it to the track they actually take. Then, by looking out how their choices change in the presence of cougar, for example, we can see if they are altering their habitat use.”

She is also looking at if humans are influencing these interactions as well. “One of the thoughts is that they might move more toward people because predators tend to be more human adverse,” Taylor shared. 

Playing Nicely

“Do they play nice?” I asked Taylor, referring to the cougars and wolves.

Though not her primary focus, Taylor told me that one of her collaborators is working to answer this very question. One thought is that cougar might move into higher elevation areas if wolves are nearby, but there are more than wolves and cougar to consider.

“Bobcats, bears, and coyotes too. All of these can eat deer and elk at some point during an ungulate’s life,” explained Taylor.

Previous research indicates that some mesopredators, like bobcat and coyotes, will change their temporal activity when apex predators, like wolves, are around. And that coyotes and bobcats may find human interaction less threatening when apex predators are present.

Fun in the Field

We continued past a couple of gorgeous incense cedar trees growing along the trail, admiring them as we went. The forest had not changed a lot, but the trail leveled off during the last stretch to the waterfall.

I asked Taylor if there were other ways, other than trapping, that data was being gathered on wildlife populations for the Washington Predator-Prey Project.

“There is another PhD candidate, Sarah Bassing, that has over 100 camera traps set up,” Taylor exclaimed. “She is looking at interactions on a large scale.”

Taylor also told me about another way they are using camera traps to track scavenger behavior at carcasses.

Scat is also collected for most of the carnivores in the research project. “There is a couple of key pieces of information it can tell us,” explained Taylor: 1) what did the animal eat, and 2) who left the scat?  You can even use how much scatt is collected to estimate how many individuals of a species are out there.

Overall, “There is going to be three PhD dissertations, one master’s thesis, and additional papers” published around the Predator-Prey project. And hopefully a synthesis paper will be written, Taylor suggested, but probably not for many years.

Waterfalling in Love with Plants

We eventually made it to the Mima Falls. It was not particularly spectacular, but we still took a short break to take in the views and snap a couple of photos, before heading back onto the trail.

“Well, this is the type of forest I am used to…but with a little less fern and more shrub” said Taylor as we walked along through the canopy-filtered light. The forest was still mostly well-spaced young Douglas-fir.

“We run habitat surveys in the summer,” said Taylor. “We have documented three-hundred plants in the understory.”

Taylor admitted that after a long fawn and calf capture season in the winter, focusing on plants is a nice change of pace. “It can feel so relaxing,” she remarked, and “I have been able to learn a lot of plants.”

Of course, good sources of vegetation are important to deer and elk success. I asked Taylor if deer have any preference toward certain plants. Taylor mentioned a study conducted by Lisa Shipley, from Washington State University, where captive deer are observed, and what they eat is recorded “bite for bite.”Mule deer tend to prefer deciduous shrubs, such as willows and serviceberry, while white-tailed deer favor forbs such as heartleaf arnica, bunchberry, and even strawberries.

Migration

As we looped up the trail, we entered a more mature forest with several older, larger trees. While we walked, our conversation migrated back toward a theme, we touched on a bit earlier—migration. More specifically, what are the patterns of migration, and do landscape-level changes impact migratory routes.

In her Okanogan county site, where her focus is on mule deer, Taylor is particularly excited to better understand seasonal migration patterns. “Most animals move up in spring and move back down in winter,” said Taylor, sometimes moving up to 40 miles over the season. This movement is thought to occur due to changes in available browse as spring moves to higher elevations and latitudes—what is known as the “green wave hypothesis.”

A Slow Burn

However, with landscape-level changes, such as fire, Taylor suspects movement patterns will change. “I have two ideas about influences of fire,” she said, “both relating to how they reduce canopy cover. One way is it could make really good forage and they may be attracted to these areas.”

On the other hand, “the canopy cover can really block snow from accumulating.” With reduced canopy cover post-fire, snow may be deeper and reduces food access. Deep snow also reduces deer mobility when they are trying to move fast to escape a predator. The fact that “deep fluffy snow favors predators over prey is well established,” remarked Taylor. She hopes to parse out these effects.

Down Logs

Similarly, down logs can also be thought of as both helpful and harmful to deer. We were noticing a lot of down logs along this section of the trail.  First, logs “can alter the way they are moving,” hindering their ability to escape a predator. But second, logs recycle nutrients to the forest and provide habitat for other forest life.

Why should we care

By now we were more than an hour into our adventure, and I realized I had not asked one of the important questions—why should we care? And, of course, Taylor was quick with a response.  She really knows her stuff!

“There are a couple of reasons,” she began. “Their role in the ecological community and also people really like deer and elk.”

“They are really cool because they are a species people can see and relate to and understand in a way a bobcat perhaps is not,” said Taylor. “I can go out in the field and see 50 deer!”

As for ecological benefits, deer and elk are “middlemen” in the food web—affecting both the landscape of vegetation while also supporting predator populations. There is also some evidence that they are important to transporting seeds and moving nutrients around.

Deaths

One of the most basic concepts of wildlife populations is understanding death.  So, it is not surprising that throughout our hike together, Taylor and I discussed deer and elk death at length.

“Are there any threats to deer and elk?” I asked at one point.

“There are a number of different diseases that regulate a population,” Taylor offered. Though not found in Washington State, Chronic Wasting Disease (CWD) is a potential concern for many populations of ungulates, as it spreads through saliva and tends to be more of a problem in dense areas. 

This is, of course, where predators may come in. By potentially keeping deer and elk populations less dense, diseases, like CWD, may become less of a threat. In addition, problems with too many deer, like wildlife conflict, eating crops, and vehicle collision are also lessened. There is some evidence, especially in the Eastern United States, that predator return could save lives and money.

Necropsy

Part of Taylor’s research is looking at causes of death in deer and elk.  To get a handle on this, she has also been doing necropsies—full field dissections—on the bodies of dead deer and elk found in the field. When Taylor told me about her involvement in this, I swear, her eyes lit up. “I really enjoy it,” she remarked.

The main goal of the necropsy is to see how the deer or elk died. If the animal died from predation, there will be lethal bite marks present, if that part of the carcass hasn’t been eaten. If it died from starvation or another stressor, the bone marrow turns from a “candle wax like material into red jelly.”

Another cool side project is to sample lethal bite marks for DNA and use it to identify the individual or species that killed the animal. 

When I asked Taylor if she found any pattern in causes of death from the necropsy, she could not say anything conclusive, as the final stages of data collection were still underway. However, she did note that car collisions were up there, along with predation, and occasional evidence for starvation or disease. How much each of these limits deer and elk populations is still being investigated. “We are seeing some evidence that there is some nutrient limitation,” said Taylor, “but not exclusively.”

Overall, deer and elk are not very threatened. White-tailed deer have, in fact, expanded their range. Mule deer have been on the decline, but they are not considered imperiled, at least not yet. 

Good Habitat

We hiked on, meandering through an interesting section of regenerating forest next to a thin stand of tall trees. I asked Taylor if the area would be suitable for deer and elk and was met with a resounding “yes.”

“This is a good place for cover and lots of good food to get into,” said Taylor. Also, “they love edge habitat.”

However, “in another 15 years it may not be great,” explained Taylor. The trees were planted at a high density, so as they grow taller and without thinning, they will likely shade out the understory, creating a food desert for the deer. 

Toward the end of our hike, we walked through a section of dense forest, like what we might expect for the stand of trees in front of us. The forest floor was dark and there was little vegetation—not a good habitat for deer.

Births

It was during our walk through this dense dark forest, after passing a wet swampy area that white-tailed deer would most assuredly love, that I inquired about the other half of the population puzzle—births.

In biology class, you are taught that there are K-selected species and r-selected species. K-selected species have few offspring, a low growth rate, and stabilize around a carrying capacity. While r-selected species have many offspring, a growth rate, and their population size tends to fluctuate more widely.

Where do deer and elk fit into this picture? Somewhere in between. “They aren’t laying thousands of eggs,” said Taylor, but, like an r-selected species, white-tailed deer are very fecund.  On average a white-tailed deer will give birth to 1.6 fawns a year. Their maturation time is also impressive as white-tailed deer in good condition can breed at 6 months old. Mule deer are similar with a longer maturation time, but similar growth rate. Elk, on the other hand, do not twin and may not have a calf every year—putting them on the more K-selected side of the spectrum.

White-tailed deer also fall more to the r-selected side of the spectrum when it comes to recovery. “They are moving further westward, and their range is expanding,” reminded Taylor. Some people even compare them to rats or rabbits in their ability to reproduce. “I don’t know to the extent they are overshooting the carrying capacity of the landscape, but the potential is there,” said Taylor. 

The Sign

Over two hours into our discussion and we were nearing the trailhead. It was so much fun talking to Taylor and listening to her speak with such focus and passion, I could not believe we were near the end. And we had not seen a single deer, let alone any deer track or scat!

However, just as we were wrapping up, Taylor found something—hair! Was it a sign of wildlife? Not exactly, but it did illustrate a cool feature of deer and elk.

“So, this is probably just domestic animal,” Taylor explained, but “one thing you can do to tell if it is predatory or prey is to fold it.” Predators have several layers of hair to protect against the elements and keep them warm. “These hairs won’t kink very easily,” said Taylor. “Deer hair,” on the other hand, “are really slippery and hollow, so they kink easily.” Deer hair will also fall out easily if a predator grabs them.

And there you have it. Only a few minutes later and we were back at our vehicles saying our goodbyes.

Complexity

Predator-prey relationships on the surface seem so simple. One species pitted against another; it can seem like an obvious win-lose situation. But speaking with Taylor, this kind of thinking dissolves—it is much more complicated than that.

Predator-Prey relationships are more like a dance, perhaps a tango, but with more than one partner. What happens to one population affects another, both directly and indirectly, which, in turn, may affect something else altogether. Thus, something as simple as the amount of snow on the ground or the density of trees in a forest has the potential to create a ripple effect over the entire ecosystem. As the old adage goes: we’re all in this together.

Taylor Ganz is a Ph.D. candidate at the University of Washington in Wildlife Science. She has a Masters in Environmental Science from Yale School of Forestry & Environmental Studied,  a B.S. in Mechanical Engineering from the University of Southern California, and a B.A. in Physics from Lewis and Clark College. She also has multiple years of experience as a Senior Field Instructor of National Outdoor Leadership School, and still enjoys teaching for them on occasion.