, live-trapping was begun on a heavily wooded slope
facing northwest, and a ten-acre area was trapped rather thoroughly in
the succeeding weeks. Because few traps were then available, this was
the only area that was well sampled in 1948, although diffuse trapping
was carried on over some 200 acres. On the ten-acre tract a total of 17
adult and subadult woodrats were caught, four along the hilltop rock
outcrop, six along the gully at the bottom of the slope, and seven at
intermediate levels on the slope. Judging from the many unoccupied
houses, the population on this tract had been much higher before the
study was begun. On the basis of this sample it seems that in 1947 a
population of several hundred woodrats lived on the wooded parts of the
square mile where the Reservation is located.

_Reduction of Population_

The abrupt reduction in the population of woodrats on the Reservation
cannot be explained conclusively with available data. Probably weather
played a major part, but other unknown factors must have been important
also. It is certain that the population of woodrats was high, if not at
an all-time peak, in 1947. In late February, 1948, when one of us
(Fitch) first visited the area on a preliminary inspection trip (not
concerned primarily with woodrats), houses of these rats were found to
be unusually numerous and those seen seemed to be occupied and well
repaired. Possibly the population was drastically reduced within the
next few weeks, as unseasonably cold and stormy weather occurred in
early March. For the first 12 days of March, 1948, temperature averaged
20 deg. below that of average March weather, and even colder than the
average for January or February. A reading of -5 deg.F. on March 11 set a
new low locally for the month since records were begun in 1869. The
record low temperatures were accompanied by 12.8 inches of snow. This
spell of unusually severe weather in early March coincided with the
period in which first litters of young usually are born, as most females
breed in early February and the gestation period is in the neighborhood
of five weeks. That most of these first-litter young may have been
eliminated by the unfavorable extreme of weather at the most critical
stage in the life cycle may be readily imagined although definite proof
is lacking. However, the mortality must have extended beyond newborn
young. Loss of first litters ordinarily would be compensated for by the
end of the season, si