Wildlife Habitat Models and Accuracy Assessment
NR505 – GIS in Wildlife Sciences
Bighorn sheep were historically native to the canyon lands and mountains of northeastern Oregon and western
Idaho. European settlement in the early 1900’s negatively impacted the bighorn populations. Hunting, competition
with livestock, and parasites and diseases are factors contributing to the elimination of bighorns in Hells Canyon.
In the 1970’s bighorn sheep were reintroduced to these canyon lands with varying success. The herds have been
monitored by Idaho Fish&Game among others.
More information: http://www.fs.fed.us/hellscanyon/life_and_the_land/wildlife/bighorn-sheep.shtml
In 2002 the Idaho Cooperative Fish and Wildlife Research Unit developed a habitat model describing lambing
habitat for bighorn sheep. The input habitat variables to the model are topography, distance to water, land cover type
and patch size. The criteria are as follows:
45-315 degrees aspect
31-85 degrees slope
<=1000m from streams
>=2 ha (20,000 m2)
NLCD (National Landcover Habitat Codes) = 12,31,33,51,71
code
11
12
21
22
23
31
32
33
41
42
43
51
61
71
81
82
83
84
85
91
92
covertype
Open Water
Ice/Snow
Low Intensity Residential
High Intensity Residential
Commercial/Industrial/Transportation
Bare Rock/Sand/Clay
Quarries/Strip Mines/Gravel Pits
Transitional
Deciduous Forest
Evergreen Forest
Mixed Forest
Shrubland
Orchards/Vineyards/Other
Grasslands/Herbaceous
Pasture/Hay
Row Crops
Small Grains
Fallow
Urban/Recreational Grasses
Woody Wetlands
Emergent Herbaceous Wetlands
Objectives: In this exercise we will develop a spatial model for bighorn sheep lambing habitat, perform an
accuracy assessment and learn how such models can automated and run in ArcInfo AML (arc macro language) code.
The developed model is a spatial binary model where each pixel is either a 0 or 1 (habitat or non-habitat) within the
Redbird herd on Craig Mountain.
Step 1: Open a new ArcMap project and add the following data:
Herd_nlcd
Herd_dem
Strms
National Landcover
Digital elevation model
Streams
Raster - 30 m pixels
Raster – 30 m pixels
scale 1:100000
1
Step 2: Derive aspect and slope from the DEM. First set the analysis properties for the analysis, i.e. define the
working directory, analysis extent and pixel size. You do this in the Spatial Analyst menu under Options.
 Set the working directory to c:\nr505\data\bhs_data (or any other folder where you want your resulting
grids to be stored).
 Set the extent to ‘same as Herd_dem’
 Set the Cell size to 30
Spatial Analyst is an Extension in ArcGIS used for analysis of RASTER data. If you don’t
have the Spatial Analysis toolbar – go to View – Toolbars and check ‘Spatial Analyst’.
If the toolbar is present but all tools are ‘grayed out’, go to Tools – Extensions and check
Spatial Analyst.
Select Surface Analysis and then ‘aspect’ in the Spatial Analyst menu. The input surface is herd_DEM, the cell size
is 30 and then name the output raster ‘herd_aspect’. The aspect grid is a grid where each pixel represents the
azimuth at that particular location. The azimuths are expressed as decimal numbers and the grid does therefore not
have a table – you cannot view the attributes.
Similarly, derive slope in degrees.
Step 3: In this step you will derive a new grid ‘distance to streams’ based on the stream vector data. Set the Analysis
mask under Spatial analyst Options to ‘herd_DEM’. This limits the ‘distance to streams’ to the area of interest.
 Under Spatial Analyst – Options – General, set the analysis mask to the ‘herd_DEM’ layer.
 Go to Spatial Analyst – Distance – Straigh line distance
Distance to: strms
Max dist: set to 10000 or so
Cell size: 30
Name the output raster:
‘Str_dist’ for example
Each pixel in the new grid represents the
straight line distance to the nearest stream.
Step 4: You are now ready to query for suitable lambing habitat for bighorn sheep. We will use the Raster
Calculator tool in Spatial Analysis drop-down menu to find areas vegetated with NLCD land cover types
12,31,33,51,71 , less than 1000 m from a stream, 45-315 degrees aspect and on 31-85 degrees slope.
You can type in the entire query and once (big chance of making a mistake) or query for each variable at a time (the
sensible option).
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First query for the land cover classes as
follows:
Double-click on ‘herd_nlcd, click ‘=’ click
on 1 then 2, click ‘or’, double-click, doubleclick on ‘herd_nlcd, click ‘=’ click on 3 then
1, click ‘or’ etc.
Evaluate!
The new grid is 1 where the landcover
classes are 12-31-33-51-71 otherwise the
pixel value is 0. The grid will be named
calculation, rename the grid ‘Land Cover’.
Similarly, create a query for aspect, slope, and distance to streams.
Finally, query for areas where all queries are equal to one (all criteria are fulfilled).
The output grid has value 0 or 1, 0 – False, 1 – True.
You can find the COUNT for 0 and 1 in the attribute table.
How much bighorn sheep lambing habitat is there within the Redbird herd boundary?
Accuracy Assessment
Step 5. Add the known lambing locations to the habitat map (rb_lamb). Next you would like to find out if the points
are located in the predicted habitat (1) or non-habitat (0). This is a point – grid overlay analysis. You can do this as
follows:




Select ArcToolbox – Spatial Analyt Tools – Extraction – Sample
The name of the input raster is your habitat model
The input locations is the rb_lamb point data
Name the output table
The output table contains the x and y coordinates for the points and the value 1 or 0 that the points fall in. Count the
number of 1’s and 0’s and compute the model accuracy.
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