WSP00036

• File Number: 8200.750
• Description: San Juan River General
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/1/1975
• Author: BOR
• Title: San Juan Ecology Project - Interim Progress Report - March 1975
• Water Supply Pro - Doc Type: Report/Study

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001584

4.6 ELK (Dr. Harold Steinhoff, James Sweeney, John Sweeney)

4.6.1 Job 1. Winter Distribution (James M. Sweeney)

- Objective

To answer the following questions:

1)

What elevations, aspects, and vegetative types
are occupied by elk through the winter 8S related
to the varying snowpack?

include total precipitation, frequency of storms, and
rate of baring of the winter range. The elevation at
which elk occur during winter is related to a snow
line of a certain critical depth. The location of
this critical snow line 1s in turn related to snow-
fall patterns during the winter.

Depth of the snowpack at the Top Park fescue study
site has proven indicative of winter conditions
(Fig. 1). In the first winter of study (1970-71),
maximum snow depth (11 decimeters) was not reached
until Feb. 27, and decreased from that date on. This
could be broadly classified as a mild winter. In the
last two winters (1971-72 and 1972-73) a greater
depth (14 dm and 16 dm respectively) was reached at
an earlier date (Jan. 8 and 6 respectively). The
snow was almost this deep already in early December.

The winter of 1971-72 reached a peak on January 8 and
decreased from that date on. It could be classed as
severe at first, but mild at the end. The last
winter, however, should be described as severe
throughout. Instead of showing a decrease in snow
after January, the snow depth continued to increase
until March 31 to a maximum depth of approximately
24 dm.

This past winter's flights (15.9 hrs. flight time)
over the study area resulted in 465 elk sightings.
These sightings indicate that elk began their down
slope migration at a time similar to the previous
winter of 1971-72 (Fig. 2). By January, however, the

1971-72

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2)

What is the critical depth of snow for elk on
Missionary Ridge?

FEB

MAR

APR

MAY

- Hypotheses

1) The upper elevationsl limit of elk in winter is
dependent upon a critical snow depth, that depth
most likely being between 65 and 75 cm.

2) The critical snow depth for elk varies signifi-
cantly with abundance of available food, snow
hardness, and degree of slope.

3) Elk tend to occur on a south aspect where food is
available.

- Findings

E1evation-

Down slope migration patterns of elk in the winter
vary with severity of the winter. "Severity" would

24

o

NOV

DEe

JAN

Figure 1. Snow depth at The Top Park f~scue study site, Missionary Ridge.

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