Population Dynamics for Tracking Wildlife Populations Through Time
In wildlife conservation and management, population estimates are highly desired information and tracking them gives important insights about the health and resilience of a population through time. For example, Wisconsin Department of Natural Resources (WI DNR) annually estimates the size of the deer population in more than 80 Deer Management Units (roughly the size of counties). Fun fact – Snapshot Wisconsin contributes data on deer fawn-to-doe ratios to make these population estimates possible.
Annual population growth can be estimated by dividing the population estimate in the current year by the population estimate in the previous year (we call this growth rate lambda). A lambda = 1 is a stable population, a lambda < 1 is a declining population, and a lambda > 1 is a growing population.
Examples of graphs showing stable, growing, and declining populations based on their lambda value.
What leads to the stability, growth, or decline of a population is the foundation of population dynamics. Population dynamics are a way to understand and describe the changes in wildlife population numbers and structure through time. The processes for growth are births and immigration into the population, and the processes for decline are deaths and emigration away from the population, which leads to the following formula at the heart of population dynamics:
Population size this year = Population size last year + births – deaths + immigrants – emigrants
These young turkey poults would contribute to the number of “births” in a population estimate for turkeys.
This cottontail fell prey to a red fox. Animals that have died would contribute to the number of “deaths” in the population estimate for their species.
In established wildlife populations we often focus solely on the births (called recruitment) and deaths within a wildlife population and assume immigration and emigration are equal and therefore cancel each other out.
For deer, the birth part of the equation is captured by those fawn-to-doe ratios mentioned earlier, and the death portion is estimated as a combination of mortality sources. One source is deer harvest, and because Wisconsin requires registration of harvested deer, we have a pretty good understanding of this mortality source. Other mortality sources are from natural causes and are best assessed through radio-collaring and tracking deer through their lifetimes.
This deer is part of the WI DNR’s radio-collar tracking program.
Bobcat and fisher are two other Wisconsin species whose births and deaths are estimated annually. For these species, the recruitment into each population is estimated from our understanding of how many kittens (bobcat young) and kits (fisher young) are born into the population. The data come from the reproductive tracts of harvested females. The reproductive tracts contain scars for each placenta that was attached, thereby providing information on pregnancy rates and litter sizes. Similar to deer, information on mortality in these population comes from registered harvest and estimates of other non-harvest sources of mortality collected from radio-collaring research studies.
A bobcat with a WI DNR radio-collar.
Bobcat kittens captured on a Snapshot Wisconsin trail camera.
We are developing ways for Snapshot Wisconsin to contribute to our understanding of wildlife population dynamics. A real value of Snapshot Wisconsin is that it tracks all types of wildlife. For each species, we can develop metrics that will help us better track its population dynamics, and therefore gain a better understanding of the current status and trajectories of our wildlife populations.
One of these metrics is the proportion of cameras that capture a photo of a species within a time and spatial area. We can treat this metric as an index to population size, which is very useful for tracking populations across space and time. If we see a trend in the proportion of cameras in some part of the state showing an increase or decrease in this metric, that gives us information about the distribution and movement of species. For example, the southern border of fisher distribution in Wisconsin (currently around the center of the state) has been thought to be shifting further south. This metric can help us document when and where this shift may be occurring. This metric is now tracked for 19 Wisconsin species on the Snapshot Wisconsin data dashboard.
In the following graphics, you can see the proportion of trail cameras detecting bobcat in each ecological landscape of Wisconsin in 2017, 2018 and 2019. The patterns are consistent across these three years and show the distribution of bobcats is across two-thirds of the state. We will be tracking this metric and others for bobcats, as well as for other Wisconsin species.
Maps showing proportion of bobcat detections on Snapshot Wisconsin cameras in different ecological landscapes in 2017 (far left), 2018 (middle), and 2019 (far right).
The power of Snapshot Wisconsin is just beginning to emerge as we are collecting consistent, year-round, and multi-year data in this effort. Thanks to all of our volunteers who help make this possible!
Volunteer Highlight- River Bend Nature Center in Racine County
The following piece was written by OAS Communications Coordinator Ryan Bower for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link.
Snapshot Wisconsin volunteers have been asking to hear about unique ways others engage with the program. Today, the Snapshot Wisconsin team highlights, not an individual, but a group that manages one of the longer-running Snapshot trail cameras – River Bend Nature Center (RBNC) in Racine County.
RBNC is an outdoor environmental education center that leases and manages about 80 acres of upland and lowland forest, as well as a six-acre prairie, from the county. River Bend’s primary mission is environmental education, conservation and sustainability with a variety of programs for all ages, ranging from little tikes to seniors.
Christa Trushinsky, Naturalist and Director of Education at RBNC, has worked at the nature center since 2016 and oversees their Snapshot trail camera. “I went to grad school for Environmental Conservation, so I’m very interested in exactly what Snapshot Wisconsin does, looking at the dynamics of land and the species that use it,” said Trushinsky. Trushinsky first heard about the program from a Snapshot Wisconsin team member she went to graduate school with and got in touch with her to learn more.
Little did Trushinsky know, that connection would later play a role in developing many of the nature center’s programs.
River Bend Nature Center, Racine County, Spring 2021
A Good Fit for River Bend Nature Center
River Bend has been hosting a trail camera for four years now and has found some intriguing ways to incorporate Snapshot photos into their teaching. “Snapshot Wisconsin is such a crucial tool for what we are trying to do here, especially for species that are elusive or nocturnal,” said Trushinsky.
Trushinsky said they often use Snapshot photos in their Skulls, Skins, and Scat program to help kids identify species that they wouldn’t normally be able to see. “Since some animals are nocturnal or very elusive, we can use the images to prove that these animals are out there [in the forest] and using the landscape,” explained Trushinsky. “Seeing proof of these animals in the neighboring forest makes them real to the kids in a special way. The animals are more than
something they see on TV – they are real and nearby.”
The trail camera pictures also act as a segue to the hands-on portion of the program, where participants look for animals and signs of animals (e.g. nests, burrows and tracks). “If we find an animal that can be handled, we talk to the kids about how to do so gently and appropriately,” said Trushinsky. Sometimes the children interact with an animal for the first time, such as feeling a slug’s sliminess or a snake’s scaliness. “That’s all part of it, showing them how to handle wildlife appropriately, as well as which to respect and stay away from.”
RBNC incorporates Snapshot pictures in other ways as well. Staff have introduced the concept of predator-prey relationships to children by showing time-lapse photos of predators tracking their prey. Trushinsky recalled an example of a doe walking by the camera, and a minute later, a coyote followed closely behind. Trushinsky uses Snapshot photos to start discussions about different relationship dynamics between the species seen on the camera.
Trushinsky has also taken Snapshot images off-site and given presentations at schools and colleges. To highlight examples of camouflage, she shows participants sets of pictures from the trail camera and asks them if they can figure out where the animal is and identify it. “Basically, I introduce it as, ‘Hey, this is Snapshot Wisconsin. You guys could be doing this on your property!’ I talk about what [species] we see at River Bend and take them through the process of classifying photos. Kids especially seem to get a kick out of it,” said Trushinsky.
Learning Lessons Themselves
While most of what RBNC does is focused on educating others, they have also learned more about he land they manage by hosting a Snapshot trail camera. Their trail camera has confirmed which species inhabit their land, as well as how the species use the land at different times of the year.
The RBNC trail camera is in a unique location, tucked away in a floodplain area of the lowland forest. During the spring season, the Root River surges, spilling over into a nearby pond, flooding the lowland forest. The flooding dramatically changes the landscape around the camera. Herons, wood ducks, mallards, and other birds can be found wading and swimming in the forest around the camera. Since RBNC’s camera looks out over the flooded area, they capture some great images that have excited birders who visit the nature center. “These are species you typically don’t see using a forest habitat. You might also see swimming muskrats or mink [while the area is still covered in water],” added Trushinsky. “It’s offered a great place to raise early season ducklings — with lots of cover.”
As the season shifts towards summer, the water drains, and a new batch of animals begins to use the area. Tall grass soon fills everything the camera sees, and species like deer move in. Does raise their fawns in the tall grass, and other little land creatures start to emerge.
Trushinsky said the trail camera pictures tell such a different story every season, with different animals showing up and using the land in their own unique ways. “The Snapshot camera helps us see what species are out there and if there are any novel or threatened species we need to be aware of. The presence of these species may even impact our land use plans,” said Trushinsky.
To date, RBNC’s camera has seen deer, opossums, raccoons, mink, muskrats, coyotes, mallards and great blue herons at this single camera location, just to name a few. They have also been able to identify certain butterfly and bird species (like the golden warbler) from the images, even though Snapshot doesn’t currently classify these species. The RBNC staff are hoping to see a river otter this year, but they haven’t seen one at this location yet.
Trushinsky shared her thoughts on joining Snapshot Wisconsin and the center’s unique camera location. Check out the video to hear her describe the camera in her own words.
Advice for Others
Trushinsky had some parting advice for other nature centers and groups who are considering hosting a Snapshot trail camera. “Snapshot is something very easy to get into and do. There isn’t that much of a time commitment needed. You can leave the camera out there and check it every three months. The biggest time commitment is just getting to the camera and classifying the photos.”
Trushinsky also shared some of the little tricks that she has discovered over the years.
- Make sure the camera is in a place where you already see signs of wildlife. You won’t capture many photos of animals if wildlife aren’t using that area.
- Put the camera in a location that is harder for people to get to, especially if you have people who visit your land. Whenever you go out there, you leave a scent, which can impact how animals use the area. It’s good to use the same route to the camera with each visit.
- Be ready to thaw a frozen lock in the winter. Trushinsky learned that one the hard way.
- Be prepared—wear mosquito repellent or longer layers in the summer and burr-resistant clothing in the fall. If you go through tall grass to get to your camera, always check for ticks in the spring!
- Be aware that there may be a lot of little bugs that like to make their home inside of the camera case. Bring a tool or rag to remove them if you don’t like insects.
- If you are using a tree to mount your camera, don’t forget to loosen the cable lock or strap on it – that allows the tree to continue to grow.
If you are thinking about hosting your own Snapshot trail camera, check out the Snapshot Wisconsin website or visit the Apply to Host a Trail Camera page! You never know what you might find in your area.
Snapshot and Satellites: A Creative Pairing
The following piece was written by OAS Communications Coordinator Ryan Bower for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link.
A few months ago, the Snapshot team said farewell to someone who has worked with the Snapshot Wisconsin team for several years. John Clare, a former graduate student at the University of Wisconsin-Madison, completed his PhD in December, 2020 and has moved on to a post-doctoral position at the University of California-Berkley.
While completing his doctoral degree, Clare worked in Drs. Ben Zuckerberg and Phil Townsend’s labs, and his research has helped push Snapshot Wisconsin to the next level, expanding the capabilities and reach of Snapshot Wisconsin. Although he played a behind-the-scenes role, one of a few students studying how to use Snapshot data in new and useful ways, his contributions to the team are appreciated, so the Snapshot team decided to share a piece of his research with those of you who follow this newsletter.
Clare first connected with Snapshot Wisconsin when current Snapshot team leader, Jen Stenglein, got in touch. Stenglein, Quantitative Research Scientist at the DNR and a leading member on the data analysis side of Snapshot Wisconsin, was interested in the sampling parameters of Clare’s Masters research, which also dealt with trail cameras. Stenglein hoped to learn from that project and apply lessons to Snapshot Wisconsin.
“I didn’t know about Snapshot Wisconsin until after talking with [Stenglein],” said Clare. “I later saw a posting for a PhD assistantship related to the program, and I applied. That is how I first got involved.”
Two beavers captured on a Snapshot WI trail camera in Ashland County.
Clare was one of the first graduate students working with the project. He initially helped get the program up, and later he started to sort through the data and deliver some useful results.
While we don’t have the space to cover everything he worked on for his dissertation, Clare and the Snapshot team wanted to share a small piece of Clare’s research with the volunteer community and showcase part of how Clare contributed to the project.
Leveraging Snapshot Data
A central goal of Clare’s dissertation was to develop strategies to better leverage the spatial and temporal capabilities of the Snapshot database. Clare mentioned that two unique features of Snapshot Wisconsin are that Snapshot operates both statewide and year-round. Many other monitoring programs can’t operate at such wide and long scales because it would be too resource intensive for them. Fortunately, Snapshot has the help of thousands of people across Wisconsin (and the globe) to overcome that resource barrier and operate statewide and year-round.
“[Using data from all over the state and from all times of the year], we can explore questions in ways we didn’t have the ability to before,” said Clare, and Clare investigated a few of these questions in his dissertation. Two of Clare’s research questions were what broad factors drive where species are distributed and how species are active across the year.
To answer both questions, Clare needed to build a special type of model that leveraged both spatial and temporal data at the same time. Not an easy feat.
Setting Up Clare’s Model
Clare needed a unique model that could account for how species are spatially distributed around the state and temporally distributed throughout the year. “I think it’s important to take advantage of both the spatial and temporal components at the same time,” said Clare. “The question isn’t just where are species located, but also how species are distributed at time x, time y and time z.”
Both the spatial and temporal scales were needed because there are components of the environment that vary strongly across space and time. Snow depth, for example, is not fixed over the course of the year. One week, there may be six inches, and the next week there may be twelve. Snow depth also varies spatially. A few miles could be the difference between seeing snow on the ground or not. Many environmental factors are highly dynamic and variable like this, so Clare needed to think of these factors within a model that accounts for both.
It is common for models to use one type of data but incorporating both is a challenge. The main challenge is having enough data (and data of the right types) to run this kind of analysis. Fortunately, Snapshot images have both location and time data attached to each image.
Another unique aspect of Clare’s model is that it considers multiple species at once. “We were pretty sure that individual species are distributed dynamically throughout space and time, but entire communities have not been heavily studied in the same way,” Clare said. “The appeal of using a spatial-temporal structure across the entire community is that we can explore which species are interacting with others at different parts of the state and at different times of the year.”
This concept isn’t new to the realm of modeling, but it is hard to accomplish. Researchers would need separate data for each additional species they added in the model. It can be hard enough getting data for one species, let alone multiple. However, that is where Snapshot shines best. Volunteers can tag up to 50 unique species in their Snapshot photos, so an equal number of species-specific datasets can be pulled and created from the larger Snapshot dataset.
“The advantage of a multispecies approach is that you can take into account the responses of each of those species, as opposed to modeling one species and assuming the results apply uniformly for other species,” said Clare.
Driving Distribution and Activity
Knowing he had the ability to answer his questions, Clare thought about which factors might be most influential across the entire community, in terms of predicting where species were located and how active they are. “We had a couple ideas about what these factors might be,” said Clare. “Some were related to seasonal variation like the amount of snow and the greenness of the vegetation.”
Snow depth can change substantially from day to day, even during the winter. Snow depth could dramatically impact how species move around and where food is available. Snow can even correlate to which species are even seen during parts of the year. For example, black bear behavior is often related to the winter, and thus with snow.
Wisconsin’s black bears sleep through the winter. Since winter is also associated with snow, black bear activity inversely correlates well (in Clare’s model) with snow. When there’s more snow on the ground, we are (most likely) deep into winter and see the least activity from black bears.
Another environmental variable that Clare was interested in was vegetative greenness. Vegetative greenness is, from space, how green the landscape looks. In the spring, trees will start to bud burst, and the grass will grow. The landscape itself will just be greener than the previous months, and more nutritional energy will flood into the food web. Vegetative greenness varies throughout the year and can impact how animals use the land, depending on when and where food is available.
For example, a black bear’s seasonal activity could reflect the cycle of vegetative greenness. Black bears maximize their activity at times of the year when there are more food resources around, either plants or prey. These times of the year may strongly correlate to peak greenness of the landscape, or so Clare theorized.
But you might be thinking, “Wait, can the Snapshot cameras measure vegetative greenness and snow depth from the trail camera photos?” The answer is possible, but more research is needed before we can use the cameras that way. Instead, Clare used daily satellite images of the state to calculate vegetative greenness and snow depth.
Linking Satellites with Snapshot Wisconsin
Clare used satellite images from NASA to measure snow depth and vegetative greenness. Part of Clare’s assistantship position was funded by a NASA grant whose purpose was to figure out ways to integrate a continuous stream of animal observations with a continuous stream of Earth observations coming from space. Between the trail camera data and the satellite data, Clare aimed to find connections that were meaningful to wildlife management.
Consider winter severity in deer population modeling, for example. Winter severity is already used by the DNR to predict the impact of winter on deer populations and plays a partial role in making harvest decisions for the subsequent fall. One hope of the NASA collaboration was to develop more integrated measures like winter severity for deer overwintering, especially ones that impact multiple species in similar ways.
Using the images from satellites passing over the state, Clare derived data on land use, surface temperature, vegetative greenness and snow depth. All of these variables were tested across spatial and temporal scales for all classifiable species.
Confirmation and Surprise
Clare wanted to share two results from his dissertation with the Snapshot community. One of these results was a confirmation of what he expected, but the other was surprising and took longer for him to wrap his head around.
“I wasn’t surprised that snow depth was a major negative driver of species activity,” Clare said. “We expected that because snow provides a refuge for some species [and a signal for other behavioral changes like hibernation].” These behavior changes cause sightings of these species to drop off during the winter and strengthens the negative correlation between snow depth and species activity. Snow is also associated with winter, when species tend to be less active to conserve energy resources.
What was more surprising was that the peak period of species activity was not associated with the peak of the growing season, or when the land was at its greenest. Clare expected these two peaks to match because there would be a maximum amount of food on the landscape. However, after some rethinking, Clare came up with a new theory about why peak activity wasn’t at peak greenness. “What we [now] think is happening is that animals don’t have to move around as much during the peak of the growing season. They don’t have to go as far to find food. It is all in one
aisle,” Clare said.
As for linking satellite data with wildlife data, snow depth and vegetative greenness both were the best predictors of species distribution and activity out of the environmental variables Clare tested. Even though vegetative greenness didn’t function how he predicted it would, it still was a good predictor of community activity and distribution. Both of these variables showed promise as potential satellite-based metrics that NASA and the DNR can use to better predict how the environment is impacting the greater wildlife community.
What’s Next?
Now that Snapshot Wisconsin has a few years of data across most of the state, Snapshot will start looking into broader trends like year-to-year weather variation and how species habitat associations may vary from year-to-year.
“As we anticipate global changes, including more extreme events like polar vortexes, heavy rain and droughts, there is a need to understand how species react to different weather phenomenon. By looking at how species are distributed at finer time scales, we can start to address those types of questions. That wasn’t the exact focus of my research, but my research can help us start to quantify what [counts] as an extreme event for different species,” explained Clare. However, that work will be done by someone else, since Clare has graduated and moved to California.
Clare took a moment to reflect on his years working with Snapshot Wisconsin. Clare said, “My favorite part has been seeing the broader project move from a concept to an operating system. It has been really exciting to see that dream come to fruition. Most of that credit is due to the folks on the Snapshot team like Jen Stenglein and Christine Anhalt-Depies.”
Clare was also appreciative of the community of volunteers that sustain Snapshot Wisconsin. “It has been rewarding to see so many Wisconsin residents get involved,” said Clare. “I’ve been blown away with how smoothly and effectively it all has worked.”
With Clare moving on to the next step of his career, the Snapshot team wishes him the best and thanks him for helping the program get set up and running, as well as his contributions on the research side of Snapshot.
Thanks John Clare, and good luck!
What Makes Data “Good”?
The following piece was written by Snapshot Wisconsin’s Data Scientist, Ryan Bemowski.
Have you ever heard the term “Data doesn’t lie”? It’s often used when suggesting a conclusion based on the way scientific data tells a story. The statement is true, raw data is incapable of lying. However, data collection, data processing, data presentation and even the interpretation can be skewed or biased. Data is made “good” by understanding its collection, processing, and presentation methods while accounting for their pitfalls. Some might be surprised to learn it is also the responsibility of the consumer or observer of the data to be vigilant while making conclusions based on what they are seeing.
Data Collection
Thanks to the data collection efforts of more than 3,000 camera host volunteers over 5 years, Snapshot Wisconsin has amassed over 54,000,000 photos. Is all this data used for analysis and presentations? The short answer is, not quite. Snapshot Wisconsin uses a scientific approach and therefore any photos which do not follow the collection specifications are unusable for analysis or presentation. Under these circumstances, a certain amount of data loss is expected during the collection process. Let’s dive more into why some photos are not usable in our data analysis and presentations.
Data Processing
When data is considered unusable for analysis and presentation, corrections are made during the data processing phase. There are numerous steps in processing Snapshot Wisconsin data, and each step may temporarily or permanently mark data as unusable for presentation. For example, a camera which is baited with food, checked too frequently (such as on a weekly basis), checked too infrequently (such as once a year), or in an improper orientation may lead to permanently unusable photos. This is why it is very important that camera hosts follow the setup instructions when deploying a camera. The two photo series below show a proper camera orientation (top) and an improper camera orientation (bottom). The properly oriented camera is pointed along a flooded trail while the improperly oriented camera is pointed at the ground. This usually happens at no fault of the camera host due to weather or animal interaction but must be corrected for the photos to be usable for analysis and presentation.
A properly oriented camera (top) compared to an improperly oriented camera (bottom).
In another case, a group of hard to identify photos may be temporarily marked as unusable. Once the identity of the species in the photo is expertly verified by DNR staff, they are used for analysis and presentation.
Data Presentation
Usable data from the data processing phase can be analyzed and presented. The presentation phase often filters down the data to a specific species, timeframe, and region. With every new filter, the data gets smaller. At a certain point the size of the data can become too small and introduces an unacceptably high potential of being misleading or misinterpreted. In the Snapshot Wisconsin Data Dashboard, once the size of the data becomes too small to visualize effectively it is marked as “Insufficient Data.” Instead, this data is being used for other calculations where enough data is present but cannot reliably be presented on its own.
Snapshot Wisconsin Data Dashboard presence plot with over 5,800,000 detections (left) and a similar plot with only 72 detections sampled (right).
Let’s use the Data Dashboard presence map with deer selected as an example. The photo on the left contains 5,800,000 detections. A detection is a photo event taken when an animal walks in front of a trail camera. What if we were to narrow down the size of the data that we are looking at by randomly selecting only 72 detections, one per county? After taking that sample of one detection per county, only 12 of the detections had deer in them, as shown by the photo on the right. The second plot is quite misleading since it appears that only 12 counties have detected a deer. When data samples are too small, the data can easily be misinterpreted. This is precisely why data samples that are very small are omitted from data presentations.
There are a lot of choices to make as presentations of data are being made. We make it a priority to display as much information and with as much detail as possible while still creating reliable and easily interperatable visualizations.
Interpretation
In the end, interpretation is everything. It is the responsibility of the observer of the data presentation to be open and willing to accept the data as truth, yet cautious of various bias and potential misinterpretations. It is important to refrain from making too many assumptions as a consumer of the presentation. For example, in the Snapshot Wisconsin Data Dashboard detection rates plot (shown below), cottontails have only a fraction of the detections that deer have across the state. It is quite easy to think “The deer population in Wisconsin is much larger than the cottontail population,” but that would be a misinterpretation regardless of how true or false the statement may be.
Remember, the Snapshot Wisconsin Data Dashboard presents data about detections from our trail cameras, not overall population. There is no data in the Snapshot Wisconsin Data Dashboard which implies that one species is more populous than any other. Detectability, or how likely an animal is to be detected by a camera, plays a major role in the data used on the Snapshot Wisconsin Data Dashboard. Deer are one of the largest, most detectable species while the smaller, brush dwelling cottontail is one of the more difficult to detect.
So, is the data “good”?
Yes, Snapshot Wisconsin is full of good data. If we continue to practice proper data collection, rigorous data processing, and mindful data presentations Snapshot Wisconsin data will continue to get even better. Interpretation is also a skill which needs practice. While viewing any data presentation, be willing to accept presented data as truth but also be vigilant in your interpretation so you are not misled or misinterpret the data presentations.
Exploring Signs of Spring with the Snapshot Wisconsin Data Dashboard
Everyone has a certain seasonal change that tells them spring is around the corner. For me, it’s seeing the crocuses pop up in the yards around Madison, along with hearing the red-winged blackbirds trill in the tall grass. Below are a few examples of Wisconsin wildlife and plants to look for as the snow melts and the temperature and daylight increases.
You can explore the seasonal patterns of different species on the Snapshot Wisconsin Data Dashboard. The Data Dashboard is updated with data from our trail cameras over time. To check out current data as of spring 2021, select a species from the list on the left side. Then, scroll over to the Animal Activity graph on the right-hand side of the page. Select the “by Month” option beneath the graph in order to see what changes typically occur in March.
You’ll find some common springtime patterns captured on our Snapshot cameras, like cottontails as they are increasingly out and about. In fact, the appearance of cottontails is twice as likely in March as it is February.
Americans give a lot of power in predicting spring to the groundhog, or as we call it in the classification interface, a woodchuck. We don’t see woodchucks out and about until March on the Snapshot cameras. This is an increase from zero detections in January and February while they are hibernating.
Fishers appear on Snapshot cameras more in March than during any other time of the year! This might be because they usually give birth in February and mate in March and April, so there is a lot of activity in the fisher lifecycle during this part of the year.
One of the most recognizable signs of spring is the return of bird species. You can see that Snapshot cameras capture a huge jump in detection of Sandhill cranes starting in March as they return north.
Although Snapshot Wisconsin is a project focused on the fauna in our communities, there are also a bunch of neat flora to look out for as spring comes around. Keep your eyes out for pussy willows, daffodils, Siberian squill, and other trees, shrubs and ground cover that will begin to blossom in the background of our trail camera photos.
And if you are curious about firsts elsewhere, the USA National Phenology Network posts the status of spring across the country. You can watch as spring comes to different regions and track trends, temperatures, and species as you await the arrival of spring in your own backyard.
Individuals Matter Too! – When You Can ID Them
The following piece was written by OAS Communications Coordinator Ryan Bower for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link.
Elk are similar to deer in that they lack identifiable markings most of the time. This makes it hard to know whether an elk in one photo is the same elk that appears in another photo. However, some elk in Wisconsin have uniquely numbered collars, making it possible to identify one individual elk from another.
Using these collars, researchers can piece together all the Snapshot photos of that elk and follow its movement through time. Knowing that the elk in two different photos is the same individual holds a special type of power for researchers and tells them extra information about the size of the elk herd. That is, if the researchers can leverage that additional information.
Glenn Stauffer, Natural Resources Research Scientist within the Office of Applied Science, is leading the initiative to identify individual elk and use these data to improve the annual elk population estimate. Stauffer said, “I was approached because of my quantitative modeling experience to evaluate different ways of using the elk photographs as data to fit an elk model. [Collectively,] the various models I and others have worked on provide a range of options to estimate the [elk] population size and to evaluate how reliable the models are.”
Identifying Individuals
To better understand the significance of Stauffer’s work, it helps to know how elk have historically been counted in Wisconsin.
“Long before I came onto the scene, the primary way of counting elk was to go out and count them all,” said Stauffer. This method requires extensive time in the field and considerable local knowledge about where elk groups often hang out. Researchers could count some elk by their numbered collars, but they also needed to know how many uncollared elk were in each group. The elk herd grew over the years, and more and more elk did not have identifiable collars. This added another challenge for researchers who were trying to count all the unmarked elk (and make sure they weren’t double counting any of them).
Since the estimate of the elk population size still needed to include an unknown number of these unmarked individuals, the DNR started experimenting with models that didn’t require individual identifications. These new models were also a boon because the herd was reaching too large a size to efficiently collar. It was becoming too much of a time investment and was expensive.
Instead, these models are based on images from the Snapshot camera grid, as discussed in the previous article, but even these camera-based models had room for improvement. Thus, Stauffer began researching a model that incorporated the best of both approaches: a model that was based on the camera data but still incorporated limited individual identification back into the model.
Stauffer’s Model
Stauffer looked into a variety of models but zeroed in on one type of model in particular. Stauffer explained that this model belongs to a class of models called spatial mark resight models. Spatial mark resight models combine the best of both marked and unmarked models. Stauffer’s model identifies individuals by their collars but also makes inferences from the photos of unmarked elk at the same time.
Spatial mark resight models also relax a major assumption made by the previous camera model, the closure assumption. “This assumption states that the number of elk at a particular camera location doesn’t change from one encounter occasion to the next, and it is clearly violated. Elk are wandering from camera to camera,” said Stauffer. Stauffer’s hybrid model relaxes the closure assumption and attempts to figure out the minimum number of distinct elk it can identify from the pictures.
Collared elk are often easy to identify in the photos. These collared elk are given the ID assigned to their respective collar number so that all photos of a particular elk share the same ID. The model also attempts to assign IDs to uncollared elk in the photos. The model uses probabilistics to assigns IDs to all remaining elk – either uncollared elk or unknown elk (because the collar or the collar number isn’t visible in the photo) – based on characteristics visible in each photo.
Fortunately, Stauffer’s model uses as much information as it can get from the photos when assigning IDs. For example, if one photo is of a calf and another photo is of a cow, then the model won’t assign the same ID to these animals. After all, we know those are two distinct elk, not one. Similarly, a marked but unidentified elk with one collar type can’t be the same as another unidentified elk with a different collar type. The model even uses spatial data to differentiate unmarked elk from two different photos. For example, photos at two locations close together might be from the same elk, but photos from two distant locations probably represent two different elk.
Capitalizing on all the information available in the Snapshot photos, the model makes an estimate of how many elk are likely in Wisconsin’s elk herds. As the elk herds continue to grow, this modeling approach helps estimate the elk population and hopefully saves the DNR time and money.
How well does the model work?
“[Technically,] the spatial count model doesn’t require any information about individual IDs, but it performs pretty poorly without them,” said Stauffer. “There is a series of papers from about 2013 on that shows if you add information about individuals to spatial counts, you can really improve the accuracy and precision of the spatial model.”
“Theoretically, this makes the model estimates more precise,” said Stauffer. To check, Stauffer collaborated with a colleague to run a bunch of simulations with known, perfect data, and the model worked reasonably well. These simulation results are encouraging because the model wasn’t massively overpredicting or underpredicting the number of elk in the herds, both of which could have management implications for elk.
When asked if identifying individuals from photographs is worth the extra effort, Stauffer said, “Working with models that don’t require individual IDs still requires considerable time to classify photos. Identifying individuals is only a little bit more work on top of that. In general, when you can’t meet the assumptions of a model, then it is worth getting individual identifications, if you can.”
Just how much additional effort should be put into individual IDs? Stauffer believes part of the answer comes from asking what other information can be obtained from the collars. “If we are already putting the collars on those we capture or release, then we might as well get as much out of them as possible, such as through using photographs [like Snapshot does],” said Stauffer.
Incorporating Another Year
After the Snapshot team finishes assembling the 2020 elk dataset, a large dataset comprised of the data from all the Snapshot photos of elk in 2020, Stauffer will run his model using this new dataset and generate an estimate of last year’s final elk population. Stauffer’s estimate will be closely compared to other estimates generated by the previous camera-based models and through collaring efforts alone to see how well each approach performs.
Stauffer took a minute to reflect on his work so far with the elk population estimate. Stauffer said, “The modeling process has been really rewarding, diving into this topic in a depth that I would not have done if I did not have this Snapshot photo dataset to work with. The simulation also went well. It illustrated that the model works the way we claim it works, which is good. Fitting the model to the elk data is mostly encouraging, but it shows that there are situations where it doesn’t do as good of a job as we hoped. Specifically, for calves, it still needs to be fine-tuned.”
From physically counting elk to modeling counts of only unknown individuals to modeling counts of both unknown and known individuals, Wisconsin’s approach to estimating elk abundance has evolved through time. Chances are, as the composition and distribution of the herd changes in the coming years, the approach will evolve even more. But for the next few years, Stauffer’s work will help direct how we count elk now.
Elk Snapshots Mean Better Elk Modeling
The following piece was written by OAS Communications Coordinator Ryan Bower for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link.
At the start of every year, DNR staff begin compiling a large dataset of elk sightings from the previous calendar year, and the data, once compiled, is used to calculate the total number of elk that live in the state. This method has been a standard practice since the second reintroduction of elk to Wisconsin.
What some of you may not know is that Snapshot plays an important role in counting elk by providing sightings, particularly of bulls. In fact, Snapshot has more than 250 of its cameras (over 10% of all Snapshot cameras) dedicated to monitoring elk alone. These cameras are clustered in the three areas of the state with part of the elk herd – Clam Lake, Flambeau River and Black River Falls. These elk cameras are arranged into a grid-like pattern in each area, just like the rest of the Snapshot grid, except that the density of cameras in the elk grid is a lot higher.
A few members of the Snapshot team are among those working on the 2020 elk dataset, so the team decided to focus this newsletter on elk and how they use photos to learn about the elk herd.
The Snapshot team invited Dr. Jennifer Price Tack, Large Carnivore and Elk Research Scientist and fellow scientist within the Office of Applied Science, to add her perspective to this newsletter on why Snapshot’s photos matter for elk.
The task of integrating Snapshot data into the elk model was originally the work of Joe Dittrich, who laid a solid foundation for Price Tack. Since Price Tack joined the Office of Applied Science at the end of 2019, she has been using Snapshot data to model how various quota alternatives will affect the elk herd size in the years to come.
“My research focuses on [elk] populations because populations are the scale at which we manage wildlife,” said Price Tack. Population is the starting point for all decisions that are made about managing wildlife in Wisconsin. The status of a population determines how decisions are made, policy is framed, quotas are set, permits are allocated, and so on… Population is the unit of concern for the DNR.
Price Tack continued, “While individual animals are important and make up a population, our ability to manage them breaks down some at the individual level, [simply] due to the infeasibility of monitoring individuals.”
For species like elk, which normally lack easy-to-identify markings, individual identification is often difficult. Possible, as discussed in the next article, but difficult. Thus, populations tend to be the scale of most species work at the DNR, including Price Tack’s work on elk.
As Price Tack walks us through her research on the elk population, check out the unique way that Snapshot photo data are used to monitor this large herbivore population.
Feeding Photo Data Into The Model
Photos of elk can have multiple forms of data in them, beyond just what animals are present in the picture. There is camera location data, for example, which provides information about which areas of land the elk are using and not using.
There is also movement data. The Snapshot team learned that elk calves, cows and bulls have different movement patterns and are seen at different rates throughout the year. When bulls are the most active, for example, cows tend to be less active.
The camera data also helps Snapshot determine a calf-to-cow ratio for elk. Although, it isn’t as simple as dividing all the calf photos by the number of cow photos. Cows move around more than calves do and are more detectable in photos, given their larger size. Using knowledge about calf/cow visibility, calves and cows are modeled separately, and those numbers are then used to calculate the calf-cow ratio for elk.
“I remember first learning about Snapshot and thinking it is such a cool resource! There is so much you can do with camera data.” said Price Tack. “I have experience working in other systems that use camera data, so I know [firsthand] that using camera data has a lot of benefits” – benefits like providing many forms of data at once and being more cost-effective than extensive collaring. “I wanted to tap in and work with these folks.”
Price Tack mentioned that she even had the Snapshot logo in her interview presentation. She was already thinking about how to get the most out of Snapshot’s camera data.
“Now that I’m here, my focus is on filling research needs to inform decisions,” Price Tack continued. “[Our research] is going to be critical to helping wildlife management and species committees make informed decisions for elk, such as deciding elk harvest quotas in the upcoming years. Snapshot data is one tool we can use to fill those research needs. It is available, and I’d like to use it as much as feasible.”
Besides estimating the population of the elk classes (e.g. calves, cows and bulls), Snapshot data is currently being used to help estimate population parameters and help us understand what is happening with the population. Population parameters are estimates of important characteristics of the population, such as recruitment (birth rate), mortality (death rate) and survival rates of different elk classes within the population.
Price Tack’s model uses matrix algebra to take an initial elk population size and projects the population into the future, using what we know about elk population parameters. In other words, the model can predict how large the elk population is likely to grow in the years to come. There is natural variation however, that can cause some years to be unpredictably good or bad for elk, so the model needs to be updated each year to keep its accuracy as high as possible.
Thanks to Snapshot’s camera data, we have a system in place to calculate each year’s population parameters and continue updating the model each year. This should help us catch if anything of concern happens to the population and (hopefully) fix it before it becomes a threat.
Improving the Elk Model
Another of Price Tack’s tasks related to Snapshot is improving the elk model. Many of the improvements Price Tack is researching aim to address data collection for a larger population.
The elk population was very small when the DNR first reintroduced elk to the state in 1995 and again in 2015. The DNR used intensive monitoring methods back then to collar (and track) every elk in the herd, since intensive methods are best suited for small populations. However,with the elk herd doing so well, it won’t be long before a different approach is needed. The DNR wants to transition to a method more appropriate for a larger elk population.
Currently, the DNR is early in the process of ramping up non-invasive, cost-effective methods like Snapshot monitoring and toning down the collaring effort. Although, this transition will take time, happening over the next few years.
Price Tack also mentioned another modification under consideration. Price Tack and the Snapshot team are looking into repositioning some of the cameras within the elk grid. Currently, the elk grid doesn’t perfectly align with where the elk are congregating. There are a few cameras outside of the elk range that don’t see any elk, and there are edges of the elk’s range that extend beyond where the cameras are deployed. Repositioning the cameras should mean more elk pictures, which means more elk data.
The Frontier of Camera Monitoring
The role of Snapshot in monitoring elk is evolving, and Price Tack and the Snapshot team believe it is for the better. While they can’t guarantee that Snapshot will always play a central role in collecting data on elk, Snapshot will fill this role for the next few years at least.
Price Tack said, “This is the frontier of using camera trap data for elk. Every year, new approaches to using camera trap data are being developed. That has me excited that, even though we don’t have all the answers now, more opportunities may be on the horizon.”
You can also get more elk-related news by signing up for the Elk in Wisconsin topic on GovDelivery. Joining this email list (or others like it, including a GovDelivery topic for Snapshot Wisconsin) is the best way to make sure you don’t miss out on news you are interested in.
January #SuperSnap
Check out these fawn triplets from an Oneida County Snapshot Wisconsin trail camera. Whitetail deer can have one to three fawns each spring, but twins are most common. Finding a set of triplets while classifying photos is certainly a treat!
A huge thanks to Zooniverse participant @pito for the #SuperSnap nomination!
Continue classifying photos on Zooniverse and hashtagging your favorites for a chance to be featured in the next #SuperSnap blog post. Check out all of the nominations by searching “#SuperSnap” on the Snapshot Wisconsin Talk boards.
Virtual Bald Eagle Watching Days 2021
Bald Eagle Watching Days has been an established community event in Sauk Prairie, Wisconsin since 1987. Bald eagles can often be found near rivers that provide ample fish, and the Wisconsin River that runs through Sauk Prairie has made this a perfect location for eagle watching.
With public health and safety a main concern, the annual Bald Eagle Watching Days have been moved online this year. The events will be live-streamed for everyone to watch from the comfort of their own homes and can be accessed by clicking here.
Events will take place on Jan. 16th and 23rd as well as Feb. 6th and 20th. As is custom, Bald Eagle Watching Days is kicking off with a live release of rehabilitated bald eagles!
Other exciting events include presentations on eagles in Native American culture, the wintering ecology of eagles in the lower Wisconsin riverway, bald eagle behavior, a bird of prey show, and many more!
In 2019, I was able to attend Bald Eagle Watching Days in person. Hundreds of people crowded together in a park along the Wisconsin River to witness the release of a few rehabilitated bald eagles. It was a frigid January day, and I remember questioning whether standing out there was worth it. However, as the wildlife rehabilitators began to prepare the eagles for release, I decided it was definitely worth it. As far away as I was, I remember being awe-struck by how large they were. The rehabilitators told us the story of how the eagles had come into their care, and then with a huge woosh, one by one they soared into the air. A hush fell across everyone at the park as we were all overcome by strong emotions. Viewing these magnificent raptors online may not be exactly the same experience as seeing them in person, but I have no doubt that their majesty and power will be conveyed just the same. Help send them off with your support and well-wishes by tuning in on January 16th!
Partnering with the Natural Resources Foundation and a New Snapshot Store!
The following piece was written by OAS Communications Coordinator Ryan Bower for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link.
Some of our volunteers may already know that Snapshot Wisconsin recently partnered with the Natural Resources Foundation of Wisconsin (NRF), but we at Snapshot haven’t shared many of the details about this partnership yet, including new opportunities available to volunteers and a Snapshot merchandise store!
Christine Anhalt-Depies, Project Coordinator for Snapshot Wisconsin, virtually sat down with Cait Williamson, Director of Conservation Programs within the NRF, to chat about what this partnership means to their programs, as well as highlight how their volunteers benefit from this partnership.
What is the Natural Resources Foundation of Wisconsin?
The NRF is a non-profit foundation that is all about funding conservation work. The NRF has a long history of supporting the DNR’s priority projects, especially those that involve species with the greatest conservation need. The NRF also connects people to conservation opportunities throughout the state through their Field Trip program, the Great Wisconsin Birdathon and many other funded programs.
The NRF was established in 1986 after significant cuts to the DNR budget. The DNR leadership at the time recognized a need to have an independent foundation to bridge private sector support for natural resources and conservation work being done, so the NRF grew to fill that need.
Williamson added, “We support over 200 different projects each year from small-scale school projects to large-scale conservation projects, even [projects] at the federal level. Our niche is conservation funding, leveraging resources from corporations, foundations and individuals. Putting those financial resources to the highest priority conservation needs for Wisconsin.”
Snapshot Wisconsin fits well into the types of projects that the NRF funds, so this partnership was a natural fit. Plus, forming this partnership had a special twist in store for Anhalt-Depies and Williamson.
Forming this Partnership
Anhalt-Depies and Williamson first sat down over coffee over a year ago to discuss forming this partnership. However, the meeting was more than just a brainstorming session about what the partnership would look like. It was a reunion for Anhalt-Depies and Williamson.
The pair first met while Anhalt-Depies was working on her project for her master’s degree nearly a decade ago. Part of the project involved radio-collaring wolves, so Anhalt-Depies collaborated with the DNR. Meanwhile, Williamson was an intern with the DNR, assigned to work with the wolf program. Anhalt-Depies and Williamson worked together very closely for months until the field work was done, then they went their separate ways.
Anhalt-Depies later went on to work with Snapshot Wisconsin and eventually became the project coordinator. On the other hand, Williamson started working at the NRF and became the one who builds partnerships with the DNR (and other conservation or education groups), as well as determines what the NRF’s priorities are. Williamson said, “I have the fun job of giving away the funds we help raise and knowing those are going to have the most impact they can.”
Anhalt-Depies explained what motivated her to reach out to Williamson again. “As Snapshot grew to a state-wide program, we identified the need to partner with groups that could help us expand our reach, especially in the area of supporting education. NRF seems like a natural fit, based on their goals and mission. I reached out to [Williamson]. We sat down and had a great brainstorming session about what a partnership between the two would look like and how we could help each other reach our goals.”
Williamson added, “It was fun to reconnect with [Anhalt-Depies]. We [at the NRF] have heard about and been informally in-the-loop on Snapshot Wisconsin, so it seemed like a natural fit because of what Snapshot is – engaging people and providing critical data. It was a no brainer for us.”
“It’s awesome to be able to offer yet another opportunity for our members and our partners to engage with Wisconsin’s natural resources,” said Williamson, and engage, they can. Not only do Snapshot volunteers benefit, but so do the NRF’s members.
How do Snapshot Volunteers and NRF’s Members Benefit?
Anhalt-Depies shared how this partnership benefits Snapshot volunteers. “This partnership helps expand our reach,” said Anhalt-Depies. “It brings the Snapshot program to a new audience, helping us to continue to grow.”
Anhalt-Depies continued, “The fundraising support NRF brings to the partnership will also help to increase our educational impact. Roughly 15% of Snapshot volunteers are educators. This partnership will expand the resources available to these educators, helping them to better integrate conservation education into their classroom.”
At the same time, the NRF and its members benefit from connecting to Snapshot Wisconsin. Williamson said, “From a conservation side, we [the NRF] are all about supporting priority needs for our state. Science-based conservation and the data that informs it is super critical, so we are happy to be able to support Snapshot and growing the program.”
“For our members, Snapshot Wisconsin is a really good way to connect them with something they can do,” continued Williamson. “Whether they are hosting cameras or classifying images on Zooniverse, it gives them one more way that they can give back to Wisconsin’s natural resources.”
A Message From Our NRF Partners
Another important way that the NRF is helping Snapshot Wisconsin is through providing funding opportunities, either through donations or merchandise sales. Our partners shared with us a special message for Snapshot volunteers, announcing these new ways to help out the Snapshot program.
At the Natural Resources Foundation of Wisconsin, we believe that nature has inherent value and that people have the ability to make a difference. We are the bridge connecting people who want to help with meaningful opportunities to make a lasting impact on Wisconsin’s lands, waters, wildlife and future stewards. We are very excited about our new partnership with Snapshot Wisconsin, which will connect our NRF members with meaningful volunteer opportunities, directly fund efforts that inform conservation decisions and help us learn more about Wisconsin’s amazing wildlife.
Want to show off your love for Snapshot Wisconsin and help support this incredible program? Check out our Snapshot Wisconsin storefront, featuring t-shirts, sweatshirts, hats and mugs – every purchase directly supports Snapshot! You can also donate directly by visiting
WisConservation.org/donate and designating your gift to Snapshot Wisconsin.
Between connecting our volunteers to the resources of the NRF network and new funding to expand what Snapshot is able to do, the Snapshot team is excited for this partnership. There is so much synergy between Snapshot’s goals and NRF’s mission that this partnership is a natural fit.
The partnership has also brought back together Anhalt-Depies and Williamson, and each shared some parting words for readers.
Williamson said, “Five years back, we had a visioning session about what we were really accomplishing for conservation in the state. We are not the boots on the ground ourselves, but what we do is connect people to that. There are so many ways people can make a difference. Whether it is through philanthropy, volunteering their time or just the personal choices they make to support our state’s natural resources… We are all about how people can make a difference, and Snapshot is one of those ways.”
Anhalt-Depies added, “Snapshot is people-powered research. We have thousands of volunteers who are donating their time and making a huge impact on the number of photos collected and total information gathered on our state’s natural resources. This partnership with the NRF helps to make their efforts go just a bit further, and at the end of the day, that is what matters.”
