. Brigham Young University science bulletin. Biology -- Periodicals. Biological Series, Vol. 6, No. 3, Mabch, 1965 71 itlft harsh winter months. Perhaps the small popu- lation build-up during the 1961 season was due to the winter mortaUtv during the preceding winter. Perognathus longimembris (Fig. 44) has a seasonal distribution similar to that of P. for- mosus, being active essentially from March through September. They were captured only spKjradicaUy during the winter. Striking differences in numbers frequently appeared between successive years. During 1961 the population which had been pres
. Brigham Young University science bulletin. Biology -- Periodicals. Biological Series, Vol. 6, No. 3, Mabch, 1965 71 itlft harsh winter months. Perhaps the small popu- lation build-up during the 1961 season was due to the winter mortaUtv during the preceding winter. Perognathus longimembris (Fig. 44) has a seasonal distribution similar to that of P. for- mosus, being active essentially from March through September. They were captured only spKjradicaUy during the winter. Striking differences in numbers frequently appeared between successive years. During 1961 the population which had been present the previous year in 5E had dropped considerably. No explanation is readily available for this type of yearly decline. Figure 41. Seasonal distribution of Peromyscus truei; 12E - undisturbed Pinyon-Juniper. Numbers in parentheses represent those captured with no re- captures. Males—linear bars; Females—stippled bars. summarized to facilitate a better evaluation of these data. Peromyscus truei (Fig. 41) was collected abundantly only from Pinyon-Juniper commun- ities and then primarily from the grid which had not been disturbed by nuclear weapons testing. This grid (12E) was discontinued October, 1961 because of inclement conditions and not resumed until April, 1962. The lack of sampling accounts for the sudden drop. Peromyscus maniculatus (Fig. 42) was col- lected in small numbers in all of the grids, but was abundant only in the Pinyon-Juniper. Both of the grids placed in Pinyon-Juniper were dis- continued in October, 1961 because of inclement conditions. The differences in densities between April, 1962 and April, 1961 are rather striking in each grid. The wide fluctuations are not easily explained, but could be due in part to extended home ranges of females during the supposed lactating period. PerogTUithus formosus (Fig. 43) was not col- lected during the winter months because of its inactivity. It became active during the early spring and generally remained active th
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