Research: Moose

Snowy Range Moose Project

Snowy Range Moose Project


Moose have evolved to thrive in cold-weather environments of northern latitudes, but as moose distribution has expanded south in the last century, the warmer temperatures of these regions may be challenging their ability to manage heat stress. For this cold-adapted species that lacks the ability to sweat and experiences heat stress as surprisingly low temperatures, energetic expenditures on maintaining heat balance whether physiologically or behaviorally could affect maintenance of fat stores needed for reproduction and survival. Moose of the Snowy Range in southern Wyoming occupy some of the southern-most ranges of the species, and we aim to understand how the habitats moose occupy influence susceptibility to heat stress and how that may be tied to population performance.

Our hypothesis:

We suspect that moose of the Snowy Range seek out habitats that provide good forage and cooler temperatures for these large-bodied animals. Further, we would expect that moose with access to habitats offering relatively good thermal cover would be able to achieve an energy balance necessary to promote conservation of fat stores needed for reproduction and survival.

collared moose

What's the issue?

Moose of the Snowy Range are at the southern extent of the species’ distribution, and may be more vulnerable to heat stress when compared with those of more northerly populations because of limitations in habitats that provided needed thermal refuge. Knowing the heat thresholds for Shiras moose (the subspecies that occur in the Snowy Range) and the habitats that can help mitigate the effects of heat stress is critically important for assessing the habitats needed to support healthy moose populations.

How're we tackling it?

Assessed thermal qualities of bed sites: We used GPS-collar data to identify used bed site locations of moose and characterized the micro-climate by setting up mini-weather stations at each site. We then compared daily temperatures, shade, soil moisture, and wind speeds of the used bed sites with unused bed sites to evaluate if moose were selecting for certain characteristics that made used locations cooler than others.

Portable weather station used to measure the micro-climate of bed sites

Mapped thermal landscape: Using remotely-sensed data of habitat characteristics within home ranges and micro-climate data collected from bed sites, we mapped the thermal landscape to identify areas that may serve as thermal refuge for moose.

Moose physiology: We modeled the physiological responses of Shiras moose linking measurements of body measurements, pelt color, hair length, etc. with changes in metabolism.

Thresholds of heat stress: We integrated our assessment of moose physiology with the qualities of the thermal landscape to determine how characteristics of an animal’s environment influenced metabolic demands. Linking the attributes of an individual animal with those of the environment allowed us to determine temperature thresholds at which an animal would undergo heat stress relative to the cooling properties of their immediate surroundings.

What are our findings?

Overall, moose selected for bed sites with cooler temperatures with moist or wet ground or with standing water. Moose avoided bedding down in dry, open, and sparsely vegetated (e.g., dry meadows, fire-affected areas, and sagebrush). On warm days and during the warmest part of the day moose selected strongly for wet ground and selection for standing water was through the roof on warm days! In contrast, the abundant shade offered by the forest was not sufficient to keep moose from overheating during the summer.

Overwhelmingly, wet ground was most effective at reducing heat stress, even when compared with canopy cover. On a summer day, moose could overheat at temperatures as low as 54°F (!!) when bedded on dry ground with no shade. In contrast, with wet ground and 100% shade, moose were not at risk of overheating until temperatures exceeded 82°F—which is still a fairly common temperature of summers in the Snowy Range.

What's the issue?

Beetle-kill following the mountain pine beetle epidemic of the last decade has substantially changed the structure of conifer forests, including those of the Snowy Range region. The decreased canopy cover resulting from beetle-killed trees falling can increase sunlight needed to grow vegetation of the understory (i.e., moose food) but likely reduces potential thermal refuge for moose seeking shade during the heat of day. Understanding how habitats with substantial beetle kill affect the thermal landscape for moose is needed for management of this valued species in the face of climate change and alterations to historic habitat structures.

How're we tackling it?

We GPS-collared 30 moose starting in 2015 and evaluated how moose were selecting for various habitats of the Snow Range including intact and beetle-killed conifer forests.

What are our findings?

In general, moose avoided conifer forests, regardless of the amount of beetle-killed trees within the forest. Instead, they selected for willow complexes and aspen forest. These findings suggest that moose may not actually be all that affected by beetle kill in the Snowy Range, at least at this stage in the structure of downed trees.

What's the issue?

Despite the recent colonization of moose to the Snowy Range in the 1980’s, the current status of the population is relatively unknown, but there have been growing concerns that the population may be in decline. Moose populations are often limited by habitat, because similar to other ungulates, moose commonly rely on fat stores gained from available food to finance survival and reproduction. Thus, evaluation of the relationship between nutritional condition (i.e., fat stores) and fitness (i.e., reproductive success and survival) of individual animals is often needed to understand the status of populations. Yet, the role that fat plays in population dynamics of Shiras moose (the subspecies that occupies the southern extent of the species’ distribution) is not well understood.

How're we tackling it?

Adult survival: We monitored survival of adult moose via GPS collars.

 Reproductive status: Each spring (March) we used ultrasonography to evaluate pregnancy. Each autumn (December), we then evaluated whether a moose successfully reared a calf over the summer.

 Nutritional condition: We recaptured GPS-collared moose every autumn (December) and spring (March) to measure fat reserves as they changed across seasons.

What are our findings?

Adult survival, overall, was high—>93% in summer and winter. Survival was most influenced by nutritional condition and age, in that animals in poorer condition and of an older age were more likely to die, when compared with younger, fatter animals. The cause of death of most animals was independent of disease or predators, which can have an effect on moose populations in other areas of the North American.

 

Similar to survival, the probability of both pregnancy and successful rearing of young was greater for younger and fatter animals, when compared with skinnier, older animals.

Overall, it appeared that survival and reproduction of adults are strongly tied to the age and nutritional condition of moose, highlighting the importance of how relationships among habitat and fat dynamics may influence population performance.

People working on the project:

Tana Verzuh, Alex May, Lee Knox, Embere Hall, Teal Cufaude, Corey Class, and Kevin Monteith

Funders

Wyoming Game and Fish Department and the Wyoming Governor's Big Game License Coalition.

Publications

Publications are in review and coming soon.

Find our other publications on moose Moose

Project updates

  • Project PDF download here