Climatic Changes and Effect on Wild Sheep Habitat

 ild sheep are sensitive to 

 environmental change and 

may be an effective indicator species of climate change in arctic 

and high mountain ecosystems. To 

understand the effects of climatic 

changes on Dall sheep habitat, 

U.S. Geological Survey scientists 

have been studying selected areas 

in Alaska since 2007. The research 

focus is on forage quality, nutrient levels, and changes resulting 

from warming or cooling climate 

trends. Preliminary results indicate significant changes in Dall 

sheep diet accompanying vegetation changes and upslope retreat 

of glaciers. 

W

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3060

April 2012

Climatic Changes and Effect on 

Wild Sheep Habitat

To investigate the impact of climate changes 

on traditional habitat of high-mountain large 

animals, particularly Dall sheep, U.S. Geological Survey (USGS) scientists selected 

two initial study sites in Alaska—one within 

Denali National Park and the other south of 

Fairbanks at the headwaters of the Wood River. 

Major factors considered in selecting these 

sites included accessibility, known Dall Sheep 

populations, availability of prior research data, 

proximity to moderate-to-small size glacial 

systems, and conditions that would enable 

comparison between an undisturbed sheep 

population and a heavily managed and hunted 

population. Field work was conducted at the 

Denali National Park area each year from 

2007 to 2011; the Wood River area was studied in 2008 and 2010.

Research Approach

Land-cover information for the study 

areas was primarily derived from a variety of remotely sensed data, ground-based 

observations, and existing historical 

databases. Landsat satellite imagery from 

1979, 1987, 1994, 2000, and 2007 was used 

to determine areal extent and retreat of glaciers. Change-detection datasets and other 

products will assist in determining variability in land-ice coverage and in assessing its 

relation to the health and overall condition 

of the habitat. Historical aerial photography, topographic maps, and historical 

reports provide information on snow and ice 

distribution before the availability of satellite data.

Phenological changes in the landscape 

were analyzed using MODIS, Landsat, 

and Quickbird imagery. Phenology provides information on the integrated response 

of plant species to climate as reflected in the 

timing, intensity, and duration of vegetation greenness. Global Positioning System 

points were collected along transects and 

within distinct vegetation types to aid in 

developing land-cover maps of the study 

areas. Phenological, spatial, and structural 

metrics derived from these data help define 

and characterize the observed landscapes. In 

conjunction with earlier vegetation maps of 

Denali National Park, these data will enable 

vegetation changes in sheep habitat to be 

detected and evaluated.

Wild sheep feces were collected and 

analyzed for the nutrient value, digestibility, 

and vegetation-species composition of the 

sheep diet. In addition, water samples from 

snowfield melt, permafrost melt, and glacial 

streams were analyzed for nutrient levels.

By combining the field observations with 

satellite-based products, we will be able to 

develop a reliable model of habitat change. 

Analysis of remotely sensed data will be 

coupled with the fecal analysis to assess 

change in wild sheep forage and its relation 

to climate change. Evaluation of changes in 

the overall quality of wild sheep habitat based 

on the inferred nutritional value of each landscape type will provides a means to monitor 

habitat quality through time. Once a reliable 

set of baseline data has been collected and 

analyzed, models will be developed to predict 

changes that may occur in the health (nutrient 

level) of the habitat and forage resulting from 

changing climate conditions.

Most of the research and collection of field 

data is being done by USGS personnel from 

the Western Geographic Science Center and 

located in Flagstaff, Arizona. However, in 

2008–2010 students in the Alaska Wildlands 

Program at the Wrangell Mountain Center 

collected vegetation information and Dall 

sheep feces samples in the Mill Creek Valley 

area of the Wrangell Mountains. Gretchen 

Roffler, USGS, Alaska Science Center, also 

collected Dall’s sheep feces samples in the 

Wrangell Mountains in coordination with 

noninvasive genetics research.

Research Results

Changes in glacial and snowfield extent

Landsat imagery was used to measure 

changes in glacial margins from 1979 to 

A Dall sheep feeding in typical habitat within 

Denali National Park field area.

U.S. Geological Survey scientists collecting samples in Dall’s sheep habitat, Denali National Park 

field area. In background, the massif of Denali (Mount McKinley) rises to 20,320 feet (6,194 meters).
2007 in the Denali National Park study area. 

Glaciers are shown in purple and indicate the 

extent of the glacial area that was studied—glaciers outside of the study area were 

included in order to provide more statistically 

significant sampling. Analyses showed that 

from 1979 to 2007 the mean elevation of the 

glaciers increased from 5,977 to 6,110 feet, 

an increase of 133 feet. During this same 

time the surface area of the mapped glaciers 

went from 104.2 to 55.0 square kilometers, a 

47% decline (surface area calculations take 

topography into account).

Fecal Analysis

Wild sheep feces (pellets) are collected 

and analyzed for nutrient value, digestibility 

(stress), and forage species composition and 

change. Multiple collections are made at the 

same collection sites each field season, in 

order to evaluate changes over annual collections. Significant changes in Dall sheep diet 

occurred between 2007 and 2008. Although 

consumption of grasses was nearly identical 

For more information contact: 

Edwin L. Pfeifer, epfeifer@usgs.gov, (928) 853-4633

http://sgst.wr.usgs.gov/alaska

This Fact Sheet and any updates to it are available online at 

http://pubs.usgs.gov/fs/2012/3060/

Edited by Peter H. Stauffer

Graphic design by Stephen L. Scott

Partly glaciated Dall sheep habitat in high mountain country of the Denali National Park field area.

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0 10 20 Kilometers 0 10 20 Kilometers

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1979 glacial extent

Mean elevation of glaciers: 5,977 feet

(3,448–8,783)

Surface area: 104.2 km2

On these images, the area of ice is shown in purple—the images show an approximately 47% decline in glacial extent from 1979 to 2007. 

2007 glacial extent

Mean elevation of glaciers: 6,110 feet

(3,602–8,783)

Surface area: 55.0 km2

 (47% decline)

Changes to glacial extents within and adjacent to the study area

in Denali National Park between 1979 and 2007

COOPERATING ORGANIZATION

National Park Service, Denali National Park

both years, consumption of sedges, rushes, 

and shrubs showed a sharp decline in 2008 

from 2007. Conversely, consumption of 

lichen, mosses, and forbs showed a significant increase in 2008 over 2007. No analysis 

of diet composition was performed in 2009 

and 2010. However, Dall sheep pellets are 

being analyzed for diet composition in 2011 

to see if these trends continue. 

Water Analysis

Water samples were collected at Wood 

River (July 29–30, 2008) and Denali 

National Park (August 2, 2008; July 27–28, 

2009; July 26, 2010; and August 2–3, 2011). 

The samples were analyzed in the USGS 

National Water Quality Laboratory (NWQL) 

in Denver, Colo., to determine organic and 

inorganic constituents.

Overall water analysis results showed 

low nutrient values at all sites with minimal change over time. This may have been 

because the samples were taken from locations where water was not mixed with soils 

long enough to pick up nutrients. Rainwater 

or water previously frozen in permafrost 

or glaciers would not have had the chance 

to absorb nutrients. Typically, water from 

ponds or lakes has the highest levels of 

nutrients, having had time to mix with soils 

and leafy material and absorb their nutrients.

Future Research

The observed changes in the preferred 

diet of Dall sheep between 2007 and 2008 

are striking and suggest the need for continued analysis to determine causes and effects. 

Specifically, we plan to investigate the role 

that increased or decreased precipitation and 

temperature may have on this substantial 

change. Upslope movement of woody plants 

may also have a significant impact on Dall’s 

sheep by encroaching into forage areas, 

preventing free movement between forage 

areas, and creating cover for large predators that feed on Dall sheep. Large areas of 

willow are dying out or already dead. What 

is causing this rather large willow die-off?

Are temperature and precipitation factors 

in the willow die-off, as is suspected with 

changes in Dall sheep favored forage? We 

will investigate these questions in the next 

phase of our research. 

Contacts and Collaborators:

Edwin L. Pfeifer (U.S. Geological 

Survey); Wayne Heimer (Alaska Department of Fish and Game, retired, and Wild 

Sheep Foundation, Cody, Wyo.); Gretchen 

Roffler (U.S. Geological Survey, Alaska 

Science Center); Raul Valdez (Department of Fisheries, Wildlife, and Conservation Ecology, New Mexico State University); Megan Gahl (Alaska Wildlands 

Studies Program at the Wrangell Mountains 

Center, McCarthy, Alaska)