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UW Researchers Link Habitat and Nutrition with Wyoming’s Moose Population

February 28, 2014
Man workling with moose
Brett Jesmer, a UW master’s student in zoology and physiology, poses with a captured moose in the Hoback Basin of the Bridger-Teton National Forest. Jesmer is studying the relationship between habitat and nutrition on population numbers of Wyoming moose. (Brendan Oates Photo)

A preliminary University of Wyoming report of moose habitat in five regions of the state and one in northern Colorado shows habitat is linked to nutrition condition, reproduction and calf survival in moose.

A 2013 annual report, titled “Statewide Moose Habitat Project: Linking Habitat and Nutrition with Population Performance in Wyoming Moose,” was prepared by the UW’s Department of Zoology and Physiology, the Wyoming Cooperative Fish and Wildlife Research Unit, the U.S. Geological Survey and the Wyoming Game and Fish Department.

“The Statewide Moose Habitat Project is about linking climate and habitat condition to nutritional condition, reproduction and calf survival in moose,” says Brett Jesmer, a UW master’s student in zoology and physiology, and lead writer of the report. “Results from this study are aimed at understanding the recent declines in moose calf production in the region, and to provide managers with tools with which they can monitor proximity to carrying capacity (the maximum number of animals a habitat can support) in their respective herds.”

The preliminary report looked at autumn nutrition of moose and winter habitat condition. Habitat condition and the demands associated with gestation, lactation and calf-rearing combine to determine autumn nutritional conditions, which determine pregnancy in female moose. The report was submitted to the Wyoming Game and Fish Department in January, and will eventually provide the agency with early-warning metrics to predict where and when moose declines are likely to occur.

Other contributors to the preliminary annual report are Jacob Goheen, a UW assistant professor of zoology and physiology; Matt Kauffman, associate professor and leader of the Wyoming Cooperative Fish and Wildlife Research Unit; Kevin Monteith, assistant researcher and professor of zoology and physiology; and Aly Courtemanch, a regional wildlife biologist for the Wyoming Game and Fish Department.

A numbers game

Jesmer’s report indicates that trying to define ideal numbers of moose in various areas of Wyoming is an elusive task.

“The ideal number of moose is not the same for any one area, or for any period of time due to variation in environmental conditions,” says Jesmer, who has been studying the issue, which is the subject of his master’s thesis, since fall 2011. “What that creates is a moving target of what an ideal population size should be.”

Currently, moose reproduction and calf survival throughout Wyoming is a mixed bag. In some areas Jesmer studied, recent moose calf production is increasing slightly (Jackson and Uinta, and North Park, Colo.) or remaining stable (Big Horn and Sublette).

On average, over the past three years, approximately 1,200 moose have been counted in the Sublette County moose herd, according to the Wyoming Game and Fish Department.

“This constitutes what we believe is the largest moose population in the state and in the Rockies,” Jesmer says.

In other areas, such as the Snowy Range, moose calf production appears to be declining. Up until recently, Jesmer says indications were that this moose population was growing rapidly because the mammal had been introduced fairly recently, during the mid-1980s, in a habitat that had not been intensively browsed. But numbers may now be approaching the maximum that habitat can support (carrying capacity), and this would result in decreased calf production and survival, Jesmer says.

Potential reasons for declines in calf production and factors that may impact the carrying capacity of female moose include: current and historic over-browsing of certain habitat; shifts in forage quality due to climate warming and drying; and disturbances, such as intense wildfires and bark beetle outbreak. In addition, predators in the northwest corner of Wyoming may impact calf survival; and an emerging disease, known as carotid artery worm, can cause moose to be in poor nutritional condition, go blind, have malformed antlers, cropped ears and noses, and even die.

To better understand these population patterns, the report’s objectives include:

-- Understanding the relationship between climate, habitat condition and calf production.

-- Establishing ways to measure habitat condition that can be readily used by wildlife managers.

-- Exploring alternative early-warning metrics related to nutrition and behavior to head off declines in calf production.

Moose scat offers clues

To assess the winter diet and pregnancy rates of moose, the research group collected fresh scat samples of adult moose only. To help them locate scat, the group used specially trained detection dogs from a Missoula, Mont., organization called Working Dogs for Conservation.   A cow and calf moose forage on willow in Teton County. (Mark Gocke Photo)

“They trained dogs on locating moose scat prior to coming to Wyoming,” Jesmer says. “I sent them frozen moose scat to train on.”

When fresh scat was identified in the field, researchers logged the approximate location, and habitat information was collected. Using molecular techniques in the lab, scat piles were assigned to a particular individual. The sex of the animals was determined before diet and pregnancy analyses.

The same protocols were used to characterize the range of foraging behavior and the forage quality (willow habitat and all other upland habitat types) used by moose during the summer. In this study, the sex of the animals was determined before diet and forage quality analyses.

In a process similar to that used by criminal forensic scientists, the moose DNA is duplicated multiple times, Jesmer says. Nine specific portions of the genome are “fingerprinted,” which allows researchers to identify from which individual the moose scat came from and the sex of the animal, Jesmer says.

“We can measure progesterone in the feces. That tells us if they are pregnant,” he says.

Hunters provide a helping hand

The research group also received assistance from hunters, who salvaged the kidneys of moose that Jesmer and others studied for fat content levels. Unlike humans, a lot of fat around a moose kidney is a key indicator the animal is in good nutritional condition.

The nutritional condition of cows in the fall, the mating season, determines whether they will get pregnant, Jesmer says.

“A female moose won’t get pregnant unless she has a minimum 6 percent body fat,” he explains. “The act of caring for a calf involves lactation (from the mother), and the cost of lactation will drive down the fat percentage of an animal.”

However, such assessments can be tricky. A cow could be in poor condition (i.e., have little fat) come fall because she was successful at birthing calves in the spring. On the flip side, a cow may possess healthy amounts of fat around her kidneys for the mere reason she didn’t give birth that spring.

“The cost of reproduction in females makes it difficult to link kidney conditions back to the habitat,” Jesmer says. “So, we use male kidneys. They don’t have those costs of reproduction, and the amount of fat they can accumulate represents the condition of the habitat well.”

The research group looked at 346 moose kidneys for nutritional conditional assessment during 2011-12 and another 190 in 2013.

More work to do

The research will continue this spring. The group plans to complete genetic analyses of 1,022 fecal samples and obtain finalized diet composition, diet quality, pregnancy and spring nutritional data sets. The goal is to complete the research by fall 2014 and create a final annual report.

“A future component is to assess exactly what moose eat,” Jesmer says. “We know willow is important. We have evidence they eat other things, but we’re not sure how important other diet items are.”

When all of the data is compiled, comprehensive reports will be produced for state and federal agencies, and presentations and materials will be provided to the general public. Results are expected to be published in peer-reviewed scientific journals this fall and early 2015, Jesmer says.

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