Mapping Vermont Moose Habitat Use to Aid Wildlife Managers

Feb. 7th 2023
Moose behind trees in the winter

Moose, one of the most char­ismatic and culturally important wildlife species of the northeastern United States, have declined considerably in southern parts of their range, including Vermont. Heavy winter tick infestations threaten the health, survival, and reproduction of moose populations in Vermont and the region. Vermont provides critical landscape and genetic connectivity between populations in Maine, New Hampshire, New York, and southern Quebec. 

Current and historic hunter survey data give Vermont wildlife managers a general understanding of moose habitat needs, but managers have lacked the detail that can be gained from radio collaring and tracking moose locations. They have also lacked the most up-to-date mapping technologies to examine habitat use across the landscape over time, especially considering the intricate relationship between winter ticks and moose.

To learn more about seasonal moose habitat and to identify hotspots or areas on the landscape of high use, Vermont wildlife researchers and managers monitored radio-collared moose in Essex County of northeastern Vermont. The research team from the University of Vermont (UVM), State of Vermont Fish and Wildlife Department, and Vermont Cooperative Fish and Wildlife Research Unit worked with more than 40,000 moose GPS locations collected from 74 radio-collared moose. 

“Our aim was to produce science-based information to help managers identify the habitats of importance to moose in this region and how the use of these habitats may relate to the highly complex relationship moose have with winter ticks,” said Joshua Blouin, who served as lead researcher on the study as part of his master’s work at UVM and is now a wildlife specialist with the Vermont Fish and Wildlife Department.

Using helicopters, researchers captured moose and fitted them with GPS radio-collars in January of 2017, 2018, and 2019. Researchers collared young male and female moose and mature adult females. The UVM Institutional Animal Care and Use Committee reviewed and approved all capture, han­dling, and radio-collaring procedures.

Researchers received a GPS location of a moose transmitted from each collar every 13 hours. This allowed the timing of locations to drift over time and be taken across the 24-hour period.

Researchers combined GPS locations with land cover data and high-resolution lidar (light detection and ranging) data to create maps that examined patterns of habitat use by moose. Lidar uses a laser to generate precise, three-dimensional information about vegetation height across the landscape. Lidar, combined with land cover data, allowed researchers to describe detailed habitat characteristics within moose home ranges, such as vegetation and tree heights for forage—or browsing—and forest canopy for refuge from the sun or deep snow.

A moose home range can be many square miles in area. In this study, researchers based home range analyses on 40,451 locations of 57 female moose and 17 males and a total of 219 home ranges over three years. 

Within home ranges, researchers identified land cover types important to moose during two times of year—the colder, leaf-off dormant season and the warmer, leaf-on growth season. Land cover types included deciduous (hardwood) forest, evergreen forest, mixed forest, and wetlands, derived from National Landcover Data from the U.S. Geological Survey (USGS). Researchers also considered terrain characteristics, such as elevation, slope, and aspect. 

The research team used USGS lidar data from November 2016 to characterize for­est age and height structure within each home range. Four height classifications included shrub (less than 6.5 feet tall), forage (less than 10 feet tall), cover (between 10 and 20 feet tall), and mature forest canopy (greater than 20 feet tall). 

Average home range area in the study was nearly the same during the dormant season for both mature and young female moose—about 15 square miles. Female home range areas increased during the growth season for both mature and young moose by 1.5 and 7 square miles, respectively. Male moose home ranges were much larger, about 38 square miles during the dormant season, and, similar to females, increased during the growth season to about 42 square miles.

For each individual’s home range, researchers created a Utilization Distribution, like a topographic map, of sorts, where peaks identified frequently used areas, while valleys identified areas less used or where there were fewer recorded GPS points. This allowed researchers to zoom in and examine where a moose was most likely to occur within its home range boundary. 

This mapping technology showed that how moose used the landscape differed depending on their age, their sex, and what season it was. For example, young male moose tended to use high-elevation, mixed forests more than female moose throughout the year. Young female moose used more mature canopy structure during the growth period than both adult females and young males. Adult female moose spent more time in higher elevation hardwood forests with a both canopy structure and forage close by. 

All moose sought out forage vegetation in young, regenerating forests during both the dormant and the growth seasons. This need for forage likely reflects the energy and nutrient demands that influence moose behavior. For instance, in the summer, moose feed on large amounts of forage, mostly hardwood tree leaves and buds, to meet high energy demands for lactation, rearing of young, and accumulation of fat for winter. 

Unfortunately, the places moose congregate to forage and gain fat reserves to survive winter and blood loss from winter ticks may also be where they pick up large loads of ticks in the fall. These winter ticks only survive on moose, and the prevalence of winter ticks in Vermont’s study area is shaped mainly by moose distribution in the fall (when ticks attach to moose) and in the spring (when winter ticks detach from moose to lay eggs on the forest floor).

So, areas that moose heavily use in the fall and spring, such as young, regenerating forest, may actively promote this host-parasite cycle, highlighting the concept that habitat use should not be confused with habitat quality. In another study led by Blouin, the research team found that habitat selection decisions made by adult females, during the fall when winter ticks latch on to moose, may influence whether their calves survive the following spring. The connection between moose health and winter tick ecology underlines the importance of managing for more heavily used habitat types.

Limiting the impacts of ticks on moose populations will largely involve efforts to decrease the abundance and distribution of the parasite on the landscape. This may be accomplished by reducing moose density through a permitted moose harvest or habitat manipulation to limit high-density moose congregations—which support high tick densities—and to more widely spread-out moose on the landscape.

This research and detailed understanding of moose habitat use in northern Vermont will provide wildlife biologists with a baseline of knowledge that sheds more light on moose and winter tick interactions and allow for more informed management.

“There are still many questions to address, as the relationship between moose, their habitats, climate, and winter tick infestations creates a complex ecosystem-level issue,” said Blouin. “Our contemporary maps of habitat use help identify potential hotspots, indicating areas throughout the landscape of greater importance to both moose and winter tick ecology, and will aid wildlife managers in promoting healthier and more persistent moose populations across the region.”