Thesis Watch: Sara Henslee Researches Young Moose in Northwest Alaska

By Zeke Shomler

Near Nome, Alaska, in the vast arctic landscape of Game Management Area 22, a SuperCub airplane traces the sky. In one of the two seats is Sara Henslee, a UAF Masters student in Wildlife Biology & Conservation. Below her, she sees caribou, ambling bears and of course, her research subject—the wild moose living in the Northwestern part of our state.

More specifically, Henslee’s research takes a look at moose that are 10-11 months old, or “short yearlings,” and determines what they can tell us about the future of the overall population. Her work involves aerial radio tracking of collared moose, collecting data through field work and then using it to perform several different types of analysis and population modeling. 

She conducts her field work each May from a small SuperCub fixed-wing plane, a C-185 plane or even sometimes on foot. By flying over 5,000 feet above ground level on an aircraft equipped with multiple antennae and a receiver, she can pick up Very High Frequency (or “VHF”) signals from individual collars on the wild moose. 

RADIOTRACKING - Henslee searches for radio signals on foot.

“You’re basically listening for beeps through a lot of static,” she said. “After radio tracking every day for a week, you start to hear beeping in your dreams!” 

Henslee also flies in an R-44 helicopter to locate and collar newborn calves, which allows her to collect vital data about how the moose are doing. She collects data about both calves and adults, including mass, survival rate and calving rate. 

“Short-yearlings are commonly captured and weighed by moose managers in Alaska,” said Henslee, “and there is a lot of interest in learning what the mass of a short-yearling can tell us about the future of that moose, like her future potential for producing calves or the survival of those calves, for example.”

As area manager of game species for Alaska Game Management Unit 22, Henslee’s job is to keep track of game populations in an area of coastal land that stretches all the way from the lower Norton Sound to just barely into the Arctic Circle. She does important work in monitoring populations for the purposes of hunting management. By keeping track of moose populations, she can ensure hunters have access to the meat they need while protecting the delicate ecology of game animals living in balance with humans, other species and the natural landscape. 

“I answer to members of the public who participate in limited moose hunts,” she said. “[They] remember the days of longer seasons and plenty of moose for everyone, and want to know how we can get back to that point.”

Henslee’s thesis research asks what limiting factors are preventing the population growth of low-density moose populations in Game Management Units 22C and 22D. Using the data she’s collected during her yearly surveys, she uses logistic regression models to discover what types of data are correlated with the mass of short-yearlings—whether or not the overall size of the young moose has any effect on their future reproduction. She’s also using a different model to assess which factors affect the survival of calves. Finally, she’s using all of these analyses together to create a population model to figure out the overall population growth rate of these moose. 

Ultimately, Henslee found that the moose she’s studying are “highly reproductive;” they start calving as early as 2 years old, and their rate of twinning after 3 years old is 50% or more. Both of these things are a good sign for the overall population; these moose are getting started with calving quickly, then having a lot of calves over time. “These are good indicators that the population is doing well and not close to carrying capacity,” said Henslee.

CALF: A collared moose calf poses for the camera.

She also found that the weight of her population’s short-yearling calves influences both factors of first calving age and twin likelihood. The bigger the calf, the more likely she'll start to have babies earlier and also have more twins, at least until she turns 7. This is a particularly interesting new discovery in the study of moose—nobody else has made this scientific connection yet.

“Considering moose do not experience compensatory growth,” said Henslee, “and heavy short-yearlings become heavy adults compared to lighter counterparts, I think it makes sense that heavier short-yearlings have a leg up in maximizing their reproductive success, perhaps throughout their lifetime.”

One thing that short-yearling mass doesn’t seem to affect is the survival rate of her future calves. Henslee’s research found a calf survival rate of only 18% that was seemingly random. As she explained, this is probably due to the high rate of brown bears chomping on them as easy prey.

Adult moose, however, have a pretty high survival rate. That, combined with the high reproductive rate, means that the population is still growing—not too rapidly, but it is growing. 

By studying these pieces of the moose-reproduction puzzle, Henslee is directly contributing not only to the management of the areas she works in, but other areas of low-density moose populations as well. And even beyond the direct application of her work to wildlife management agencies, this analysis helps researchers better understand the moose species as a whole, including how their reproductive output in adulthood is linked to other factors earlier on. 

Another interesting thing about these moose she’s researching, Henslee says, is the individual variation between moose. Studying populations as a whole reveals how moose each have their own personalities, choices and preferences. 

“It's important to remember that even though researchers make assumptions about populations or even species as a whole, individual animals make their own set of complicated choices every day to ensure their survival or survival of their young,” said Henslee. “It certainly keeps you guessing!”

COLLARING - Henslee holds a young moose calf as part of her field work in Game Management Unit 22.

As a professional biologist and soon-to-be M.S. graduate, Henslee has some advice for young scientists: “keep an open mind and try to get experience in as many different things as you can.” She explains that taking on tasks that pop up and offer different avenues of experience can expand your skill set and find new things you’re passionate about. As Henslee says: “you never know what might end up inspiring yo

She also explains a similar attitude toward reading: exploring your field widely by reading the relevant literature can help you find avenues of exploration, new methods to explore and get the creativity flowing that’s essential for good research design. 

“I found that reading the literature, even if it may not seem entirely relevant at first, made a huge difference in helping me identify research needs,” explained Henslee. “I struggled to gain my footing with a focused research idea at first, but now I have a handful of ideas that I want to pursue once I defend my thesis and publish my chapters. One answer seems to lead to many more questions.”

Henslee started working with the Alaska Department of Fish and Game in 2019. Before that, she earned her Bachelor of Technology degree in Wildlife Management from the State University of New York Cobleskill.

For the future of this particular research, Henslee is hoping to incorporate data from further regions to study factors like population density and other environmental conditions. Moving forward, she’s going to keep working here in Alaska to keep our moose populations healthy and well-managed.