BULLETIN FLORIDA STATE MUSEUM VOL 34(6)


 Testes of adult males regress from September through November; no
young males produce sperm during that period (Fig. 12). Spermatogenesis
begins in December, continuing into January, and by February virtually all
males are reproductively capable. In those years when young are born in
January or February, they become mature by April when the main
reproductive period begins.

 Abundance.-- In three of the four years, trap success was at maximum
following reproduction, in September-December (Fig. 13). Density declined
thereafter in each year studied, but the decline was sharper from September-
October to January-February 1981-82, the dry year, than in 1982-83 and 1984-
85, both considerably wetter years. Density in the September to December
period of 1983 was much greater than in the other years, and a "crash"
occurred in late December-early January (Fig. 13): the grid estimate taken
from 12-16 December was 769 per ha, while that obtained in an adjacent field
24-27 January, five weeks later, was 56 per ha. Migration from the adjacent
fields into the trapped field may have slightly reduced the numbers in adjacent
fields, but data from subsequent monthly catches substantiate an abrupt drop
in population density at that time of year. The abrupt decline in density was
reflected in the trap line results for the same areas, which showed a drop from
57 percent in December to 13 percent positive in January. The maximum
density recorded by grid estimates was 1125 per ha in October 1984. It
probably was higher at that time in 1983, before the crash, but no grid data are
available. Maximum trap success from line trapping was observed in
November 1983, when 68.3 percent of traps were positive for two nights'
trapping (Fig. 13).
 In relative abundance, P. natalensis comprised nearly 87 percent of the
9306 rodents and insectivores trapped on campus during the program (Table
7). The shrew Crocidura hirta was next most abundant, followed by the striped
grass mouse, Lemniscomys griselda. The other seven species taken were far
less common, although there were certainly more Tatera spp. and Mus
minutoides available than trap results indicate. These are underrepresented,
probably because Tatera could escape from "Little Nipper" traps unless
seriously injured, and because of their size Mus may not be as trappable as
other species. Dasymys incomtus was virtually restricted to deep grass, Acomys
spinosissima was both seasonal--found in April only each year--and limited to
grass areas, while Pelomys fallax was seen only in a very wet area in June 1984,
following the excessive rainfall (nearly 300 mm) of April. No permanent
streams flow through the campus, and the common name, creek rat, indicates
its preferences. Rattus rattus was common in campus houses, but only one was
taken in a field trap. The tiny, unidentified shrew appears to be truly rare, but
again, may not be trapped easily due to small size.