When I started in the wildlife profession a few decades ago, all I wanted to do was study big game and work with the iconic “charismatic megafauna,” as large mammals often are called. I made that dream a reality and worked on deer, elk and bighorn sheep projects as an undergraduate student and concentrated on bighorn sheep for my master’s degree. I read all the scientific literature diligently and learned many things in the field while spending countless hours with our magnificent big game animals.

I thought, as most students do, that I knew a lot – not all there was to know, but a lot. But when it comes to understanding nature and how the biological world works, one adage rings true: “You don’t know what you don’t know.”

I distinctly remember one key lecture in a wildlife management class from a pioneering mule deer researcher, Dr. Richard Mackie at Montana State University. Dr. Mackie once was in a camp of deer biologists who believed winter range was the sole factor responsible for sustaining mule deer populations in Montana and across the West. But in that lecture, after presenting his pioneering research on winter range as a major limiting condition for mule deer, Dr. Mackie pronounced, “We were wrong!” Had it been 2013, he might have proclaimed, “We didn’t know what we didn’t know.” He then told our class about the complexities of nature and how we have learned that several different factors influence deer populations and their ability to survive in different environments. It was an eye-opening lecture I’ve never forgotten.

Fast forward to present day. Land managers still focus heavily, and in some cases almost exclusively, on winter range as the key to protecting deer populations in the West. Winter range is important, but big game habitat use and needs during different seasons goes far beyond just protecting winter range.

One thing we’ve learned from the science on big game is that nutrition on summer and fall range is absolutely vital and that those animals entering winter range in poor condition simply won’t make it, no matter how much winter range there is or how good of a shape it’s in. But we also know that big game animals like mule deer, elk, pronghorn and caribou migrate between areas where they spend their summers and winters. What we don’t always know are the intricate details of migrations, and, in many cases, we don’t even know which populations migrate or how far.

That’s key in a new study released by the University of Wyoming Cooperative Research Unit and the Wyoming Migration Initiative. Research biologist Hall Sawyer recently set out to study a deer population near Rock Springs, Wyoming, that was thought to make only short-distance movements between seasonal ranges. To everyone’s surprise, we didn’t know what we didn’t know. Global positioning system collars (that recorded each marked deer’s location with pinpoint accuracy every three hours) revealed the longest known migration of any mule deer population – 150 or so miles from the Red Desert to the high mountains near Jackson, Wyoming.

Why is this important for mule deer? Sawyer said it best when he likened migration to driving long distances between two cities with no hotels, gas stations or grocery stores in between. Migrating animals need to freely pass through the landscape and stop occasionally to fuel up and rest. These places, called “stopover” habitats, are very important, because without them, deer could unnecessarily burn fat stores just trying to get to their winter ranges. Migration is all about finding and conserving body energy when trying to get from point A to B.

Barriers to movement or procuring food will cost some animals in the long run as they endure long, cold winters in the West. The Wyoming study identified several barriers and other management issues along this 150-mile corridor that could negatively impact mule deer. This study can help guide the management and protection of these important habitats while also pointing out the highest priority areas to target conservation dollars for easements, habitat enhancement and other management projects. That’s good news for this herd if state and federal agencies, private landowners and stakeholders work together to protect and conserve this migratory corridor. But what about other migrating herds of big game?

By learning more about what we didn’t know, scientists have solidified the need to think far beyond just one or two seasonal ranges or habitat types for mule deer populations. A more holistic view and management strategy with policy to back it is needed.

Migration corridors and habitats where big game animals rest and forage during migration are critical pieces in a complex habitat puzzle that is key to the health of populations of mule deer and other big game animals. But the science on migration has yet to make it into policy. Bureau of Land Management resource management plans do not identify migration corridors, stopover habitats or provide for their management. Now, with work like this there is an opportunity to get those lines on the map and start incorporating them into planning. That’s why the TRCP will keep working with partner groups, land managers and other stakeholders to ensure our big game populations are managed for long-term sustainability. If we do not manage and conserve key habitats on all seasonal ranges and the migratory passageways between them, big game populations likely will decline and impact both our outdoor traditions and our hunting-based Western economy.

Watch a video of the mule deer migrations: