SHERIDAN — Researchers from the Wyoming Game and Fish Department and the University of Wyoming are working together to conduct the first study of moose demography in the Bighorn Mountains.
Moose were first introduced in the Bighorns in 1948 with eight adults from the Jackson herd. Eight more followed in 1950 with 13 more each in 1974 and 1987, and all of the moose in the Bighorns today are descended from those. The 2019 trend count was 175 animals.
“Over the years, the population has fluctuated, and it’s just not that clear how many moose the Bighorns can support,” said Lindsay Martinez, a graduate student in zoology at the University of Wyoming who is participating in field work for the study and doing quantitative work to determine the results.
Martinez said the Bighorn herd is the last in Wyoming to have such a study, since research has been focused on declining populations in the western part of the state, while the Bighorn population has remained more stable.
Since March 2017, the team has put GPS collars on 60 females to study the herd’s demography and the animals’ habitat selection to better manage the herd. The team has also installed about 30 remote cameras. Through the study, they hope to gauge the performance of the population, estimating the total numbers, survival rates and calf counts.
The GPS collars have a three-year expiration date. When they fall off the animals, they send researchers a mortality signal once movement stops, allowing researchers to retrieve the collars and the movement information gathered. About half of the collars give researchers two-hour movement data while half give eight-hour data initially. The two hour data from all of them will be recoverable after they’re collected.
Martinez said the most interesting thing they’ve learned so far is that the moose in the Bighorns don’t migrate. Moose typically migrate 30 to 40 miles from summer to winter seeking lower elevations, so the behavior of the Bighorn herd is unique.
“This herd, they’re mainly residents with overlapping summer and winter ranges, so they don’t move very far,” Martinez said.
Martinez said their best guess for this unique finding is that it can take many generations to learn migration, and this herd may not have had enough generations to learn.
One collared female, however, migrated 41 miles from summer to winter.
The team has also been gathering data on willow growth in riparian river bottoms each August to measure the impact of the herd on its primary food source. Martinez said the team has found positive but low willow growth after measuring about 1,000 plants.
“Wyoming Game and Fish biologists have had some concern with the growing browsing pressure or how much of the willow community is being foraged or eaten, and so that was a part of this project, to see if it can persist with the current browsing pressure or not,” Martinez said.
Martinez said a challenge for the study is that riparian areas in the Bighorns are small and spread apart, except along the north Tongue River and the range is heavily forested. This makes it more difficult to survey the population.
When the team counts the animals, they do so in a single day from an airplane to ensure individuals are not double counted, according to Tim Thomas, a biologist with the WGFD who has been working on the study.
The collars will begin falling off in March 2020, and the researchers can begin gathering spatial movement data. Eventually the team will compare trends in the Bighorn Mountains herd with other herds across the state.
Thomas said there are currently 56 collars out, as there have been a few mortalities. When a collar doesn’t move, the researchers receive a mortality signal and can recover the collar and examine the animal. Thomas said about half of the collaring was done by aerial capture and half by ground darting.
To determine pregnancy rates, the team collects fecal samples in winter, that they can then test for the presence of the progesterone hormone. The hormone indicates pregnancy in females, giving further indication of the pregnancy rate.
Thomas said the study is funded partly by the Wyoming Game and Fish Commission and partly by the Wyoming Governor’s Big Game License Coalition, a collaboration between the governor’s office and the Wyoming Wildlife Foundation that provides five hunting licenses annually and puts the funds raised toward wildlife studies.