CASPER, Wyo. — When budding wildlife photographer Joe Riis first told biologist Hall Sawyer about his plans to photograph the newly discovered longest pronghorn migration in the world, Sawyer was, well, unsure.

“I wouldn’t say skeptical, but I knew how challenging it would be to capture those movements and also to deal with the rugged terrain and remote areas that you have to get into,” said Sawyer, the wildlife researcher who first documented the pronghorn passage. “But it didn’t take long to really see how driven he was to do what it takes to capture those images.”

Backcountry guide Wes Livingston, elk researcher Arthur Middleton, and photographer Joe Riis and their horses/mules navigate a small pond in the headwaters region of the Yellowstone River. In search of the elk summering grounds. Joe Riis, contributed

And capture he did. Riis spent two full years tracking the pronghorn as they moved from the Green River Basin to Grand Teton National Park and back again. He would wait for days for the right shot and spend weeks and even months in the field setting up motion-sensor cameras.

His pronghorn work merged into documenting the longest mule deer migration ever discovered, which then led to years tracking elk completing arduous journeys in the greater Yellowstone ecosystem.

Riis’ work has been featured in museums and galleries and the pages of National Geographic. And now it is compiled with informative essays in a hardcover book, “Yellowstone Migrations.”

“The book was a dream come true,” Riis said. “It’s a big reward for all those days spent driving around and hiking around wondering why I’m spending my life photographing these animals that walk in a line.”

After earning a wildlife biology degree from the University of Wyoming, Riis spent the last decade photographing the Wyoming migrations.

“People say ‘Man, Joe, you have the coolest job in the world. That must be awesome.’ But I don’t think people realize the amount of time and work that goes into that,” Sawyer said. “Behind every image is a month of terrible weather and living out of a backpack or truck and wet and cold and away from home and away from your friends.”

The Casper Star-Tribune caught up with Riis in between adventures in the woods to explain how he captured what would become the defining images of wildlife migration, and his views on the future of these epic journeys.

Grizzly bear on the trail of the fall elk migration in the Greater Yellowstone Ecosystem. Grizzly bears rely on elk calves in the spring and elk gut piles from hunters in the fall as significant food sources. Joe Riis, contributed

Tribune: You’ve said one of the early photos in the book of a calf panting as it treks up a mountainside is one of your favorites. Why?

Riis: It is what elk migration is all about. It’s about the calves. It’s about the moms teaching their offspring the migration path. That elk calf is about 3 weeks old. It’s learning the migration for the first time. It was born probably out on the Pitchfork by the Hoodoo Ranch outside of Meeteetse, and at that moment it just crossed the South Fork of the Shoshone River and it is crossing an 11,000-foot mountain before it drops into the Thorofare Valley, one of the most remote valleys in the Lower 48.

… I could have never imagined when I set up that camera trap, I was not envisioning calves, and then I checked that camera and couldn’t believe it. There was a 3-week-old calf with its mouth wide open on the heels of its mom and then with several calves in the background with spots on their back and their coats still wet from the South Fork of the Shoshone.

If I spent the rest of my life photographing elk, I don’t think I would get a picture like that.

It feels like migration, it feels like it’s pulsing, and really that pulsing movement of migration is the process that this book is centered around. It’s centered around the need to eat and move and reproduce.

When I look at that photo I see the need to move and the beauty of the wild planet right here in the middle of the United States. Those elk connect so many different people. There’s so many people who care about those elk, from the people who love to hunt them to the people who love to travel to Wyoming to see all the predators that those elk feed.

They’re also symbolic of the need for all of us people to work together because they travel from private lands to forest service lands to national park service lands and not one of those agencies or people can conserve the migration alone.

It’s these elk that challenge us to work together.

A buck mule deer moves up a hill near Big Sandy in the northern Red Desert on its fall migration. Joe Riis, contributed

Tribune: Do you ever worry about your presence on these migrations, that you might change the way they migrate?

Riis: That’s my number one worry about all of this work is influencing the migration. I’m concerned with being one of the threats. And sometimes I am. Sometimes the deer or pronghorn see me and they stop and turn around.

That’s why I started using camera traps in the beginning. Way back when I first showed up in the Pinedale area looking for pronghorn with (writer) Emilene Ostilund, one of the first things I realized was those pronghorn can see and sense me way before I can see them, so I had to make the decision: Do I document the migration and try and figure out a way I can do it without them seeing me, or do I abandon the project and not document them? I tried to figure it out and lessen my influence, and for me that was the camera traps. Trying to hide the camera so they don’t see it and it doesn’t make any noise and they can walk by and trigger the camera by motion, which leads to me getting the photograph and people being able to see what migration looks like and allows the animal to continue moving without being influenced.

Tribune: From a photography standpoint, are all migrations created equal, or are some easier or harder than others to photograph?

Riis: All migrations are definitely not created equal. Some span a long distance like the Red Desert-to-Hoback deer migration. But a lot of it is through a human landscape and a patchwork of ranches and forest lands and BLM and even towns. It’s much easier to be able to drive up and park and walk a couple miles to photograph that migration.

Whereas the Cody elk migration, maybe it’s only 70 miles long, but the remoteness and also vertical gain is tremendous. It’s very difficult to be able to get into those places because of the river and creek crossings. The snow depth in the spring and also knowing the trails and how to navigate the backcountry like that. I had to lean on a lot of the outfitting community just to figure out how to navigate some of the mountains. They’re inaccessible to someone like me who has never been to some of these places.

Pronghorn migrating south for the winter, caught in wire fence. This fence has a barbed bottom wire a few inches off the ground, forcing this doe pronghorn to jump the fence, and got its wrist tangled in the top two wires, a common way for pronghrn to die. Luckily, the photographer was there to pull the fence apart allowing the pronghorn to free. Joe Riis, contributed

Tribune: Are these migrations different than others you’ve photographed in the world?

Riis: Most of the past 10 years as a full-time photographer, I’ve spent most of that time in western Wyoming. This is the one theme that I have really focused on. Whereas any of the other assignments I’ve done in South America or central Africa or central Asia, they are snapshots, a one-month-long trip or so. How do they compare? From what I’ve found, they don’t compare.

In the greater Yellowstone we have this functioning system of abundant wildlife like I have not found elsewhere.

Tribune: Do you think these long migrations are sustainable?

Riis: These migrations are sustainable if we start to design our developments and our landscapes with these migrations in mind. And that means thinking real hard if we need that housing development right there or if it can be somewhere else.

A good example of that is in Pinedale on the north edge of town there, the 300-acre (area) was slated to potentially be turned into a housing development. There were enough people who came together and thought about it and realized it was not worth it. There were other places to be developed that would have a lesser impact on wild animals.

That one little chunk of ground actually impacted all of the land to the north and the land to the south with regard to the deer. There were 5,000 mule deer that it was absolutely critical they move through there. They had nowhere else to go. It was a perfect example of a pinch point, a pinch point that could have been cut off, and people came together and ensured that it was kept together for the future.

People talk about helping the migrations. The migrations don’t need help. The elk and pronghorn and deer are going to do their annual migrations if they can. Really, what it comes down to is: Are we going to allow them to do their migration? And I think we will, but it will take some serious collaboration... I think if we focus on our similarities, we will realize that a lot of us have the same wildlife values and we want to share the landscape with these animals and this wild planet.

A bull elk still in velvet walks through the Absaroka Range in this photo from the new short film “Elk River,” which documents the herd’s migration. Joe Riis

Tribune: Walk us through the process you use to ultimately track these migrations.

Riis: The process involves a lot of sitting around and looking through binoculars. Walking around. Or even driving around in places like Pinedale and you see a group of animals that are off of the road or walking along the fence. More than likely those animals are on the move. That was the first challenge for me, was to see what migration looks like. Prior to my work most of the pictures that said they were migrations were a group of animals running away. This is a slow movement. These animals are not running away.

Say there are pronghorn bunched up along the fence, so maybe I go over and look the next day or next day. Then I look at the fence and note there’s a bunch of pronghorn crossing under the fence at this spot, so I would set up a camera and leave it for three or four days and go back and check it. A lot of times animals are moving through at night, late in the day. It’s really quite simple. If you see an animal there in the road, more than likely there are others that will cross through right there…

A different example of this is a picture of a juvenile bald eagle on a pronghorn buck… So I was driving just along the Green River and saw that there was a bald eagle down on the river and I put the binocs on it and realized it was actually on a buck pronghorn that looks submerged in the water. I stopped and walked down there and realized the buck got wedged between a downed tree and rock… I put a camera on the log by the buck and had a trigger on it so I could trigger it from like a mile away… I waited the afternoon and the eagle came back and I got like 1200 pictures of it and the eagle stood on the buck pronghorn for an hour. I filled an entire memory card and it was dark and the eagle flew away and I went back out there and put my waders on and got the camera.

Tribune: Is there anything else you’d like people to know?

Riis: This project was a collaborative between a bunch of researchers, the ranching community, the hunting community, the conservation community. I interact with and work with all these different people, and in order to conserve these migrations, we are all going to need to work together.