_Specimens examined._--Total, 38: North end Mesa Verde National
Park, 7000 ft, 75984-75986; Park Point, 8525 ft., 69316-69317; Far
View Ruins, 7700 ft, 69318-69319, 79220, MV 7897/507, and 23
uncatalogued specimens in preservative; 3 mi. N Rock Springs, 8200
ft., 69320-69321; 2 mi. NNW Rock Springs, 7900 ft., 69322-69323; 1
mi. NNW Rock Springs, 7600 ft., 69324; 1/2 mi. NNW Rock Springs,
7500 ft., 69325.
The specimen listed last (69325) was an adult male recovered from the
stomach of a small (snout-vent length 334 mm., wt. 26.0 gms.) _Crotalus
viridus_ that was trapped in a Museum Special mouse-trap on a rocky
slope mostly barren of vegetation. The availability of samples taken in
August (by Anderson in 1956), in September (by Shepherd in 1958), and in
November (by Alcorn in 1957) makes the following comparison of age and
reproductive condition possible. The sample from November includes some
specimens from outside the Park as follows: 1 mi. W Mancos, Colorado,
75979-75983, and 2 mi. N La Plata [not shown on Fig. 2], San Juan
County, New Mexico, some 18 miles southeast of the Park, 75987-76000.
The data shown in Figure 3 indicate that females are pregnant at least
from in August into November. A smaller percentage of females was
pregnant in November than in August or September. The fact that all
females more than 130 mm. long were pregnant in September suggests an
autumnal peak in breeding activity. A change in the ratio of small
individuals (less than 130 mm. in length) to large individuals (130 mm.
or more in length) is indicative of a sustained breeding period
throughout the time shown. In August the ratio was 1 to 2.3, in
September the ratio was 1 to 1.2, and the ratio was 1 to 0.7 in
November. The western harvest mouse is found usually in grassy areas.