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

similar through all four years (Table 4). A marked
increase in mortality of all age classes from an
unknown sourbe, perhaps the stress of a long winter.
is a possible explanation. Patteras of these popu-
lation parameters for other species on Missionary
Ridge are either similar to those of deermice or are
not consistent enough to interpret in relation to
snow. An exception is the proportion of young
~crotus sp.. which seems directly correlated to snow
depth and may mean that adults die more readily from
snow stress than do young.

Rico-
Small mammal: populations at Rico showed a marked
decrease. but not to a lower point than 1970 (Table
3). The populations may have been at such a low
point in 1970 and 1973 that they could not be measured
precisely enough to show a difference. The deermouse
population at Rico increased in 1973. If this pattern
continues. either some environmental variable at Rico
is very different than on Missionary Ridge or we will
have evidence against the snow vs. population
hypothesis.

Associated population data (Table 4) at Rico are less
complete and do not show an interpretable pattern.

Wolf Creek-
The major decrease in the deermouse population is
consistent with Missionary Ridge. but the other small
mammal populations show an opposite pattern which is
puzzling (Table 3). Another year.of data is
essential.

Other population parameters (Table 4) likewise give
little indication of reasons for the -small mammal
'population fluctuation at Wolf Creek.

- Future Plans

Calhoun census lines will be rerun at the same loca-
tions in the same way in future years on the same
dates. July 20 to August 12. Consideration will be
given to running of extra line's on Missionary Ridge
to see if all small mammal populations on the Ridge
are varying in synchrony.

Tabla 4. Population charact ristics of small
mammals in relati to snow.
1970 1971 1972 1973
Missionarv Ridge
Number of yomg per litter
Deermou8e 1.1 5.1 5.4 5.4 5.5
Colorado Chipmunk 3.9 4.0 4.5 4.4
-Red-backed Vole 6.0 5.8 5.5 5.5
Microtus spp. 6.0 5.5 5.4 5.0
Proportion of young
.Deermouse 0.3 0.2 0.2 0.2
Colorado Chipmunk 0.1 0.1 0.04
Red-backed Vole 0.3 0.1 0.4 0.4
Microtus spp. 0.3 0.2 0.1 0.4
Fertility Rate 1/
Deermouse 1.0 0.8 1.0 1.0
Colorado Chipmunk 0.7 0.8 0.6 0.8
Red-backed Vole 1.0 0.6
Microtus spp. 1.0 1.0 1.0 1.0
Rico
Number of young per litter
Deermouse 5.0 5.6
Colorado Chipmunk 3.7 4.0 4.0 4.0
Red-backed Vole 6.6 5.0 6.5
Microtus spp. 5.0 5.4
P~oportion of young
Deermouse 0.8 0.4 0.4 0.2
Colorado Chipmunk 0.8 0.2 0.2 0.4
Red-backed Vole 0.1 0.4 0.3
Microtus spp. 0.5 0.2
Fertility Rate
Deermouse 1.0 0.7
Colorado Chipmunk 0.5 0.9 0.4 0.7
Red-backed Vole 1.0 0.9 1.0 1.0
Microtus spp. 0.7 1.0
Wolf Creek
Number of young per litter
Deer Mouse 5.5
Colorado Chipmunk 4.0 4.1 4.0
Red-backed Vole 7.3 5.6 6.5
Microt~s spp. 3.5 4.5 5.7
Pioportion of young
Deermouse 0.2 0.2 0.3
Colorado Chipmunk 0.5 0.4 0.2
Red-backed Vole 0.2 0.2
Microtus spp. 0.2 0.4
Fertility Rate
Deermouse 0.8 1.0
Colorado Chipmunk 0.9 0.7 0.3
Red-backed Vole 1.0 1.0 1.0
Microtus spp. 0.5 0.9 0.9
1/ Scientific names are giv n in Table 3.
11 Fertility rate means the proportion of mature fe-
males which give evidenc of conception during the
current ~reeding season.

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