BULLETIN FLORIDA STATE MUSEUM VOL 34(6)


population levels were at their minima, and in January, February, and April 1982--an
exceptionally dry year which drastically reduced rodent numbers. The maximum number of P.
natalensis examined in any one month was 515 in August 1984.

 Sampling technique.-- Standard line trapping with single traps set 1-2 m apart, 300-500
traps per night, was the usual method employed, normally for three nights per site. Grid
trapping when done used 300 traps on a 1 hectare (ha) grid, with three traps set per point. Points
were at 10 m intervals. The trap types employed were small and medium, collapsible Sherman
live traps, Woodstream snap-type rat traps, metal snap traps, and "Little Nipper" mouse traps.
The latter proved to be the trap of choice, being sensitive enough to take mice and shrews of 3 g
weight, simple to set, and cheap enough to be regarded as expendable. The standard bait was
dried coconut. The sampling standard chosen to compare rodent abundance from period to
period was based upon a "Little Nipper" line (LN line) of 75 traps set and checked personally by
me. The remaining traps were set by field assistants. The LN line was set adjacent to the other
lines on every occasion on which samples were taken; when grids were used, an LN line was set 10
m from one of the grid borders, for comparison. In estimating abundance from the LN line,
results from the first two nights only were considered. These were corrected by subtracting both
the number of positive traps containing other small mammal species from the total set, and one-
half the number of closed but negative traps from the total (Hanney 1965), to provide a net
number of traps set, against which the number of traps positive for P. natalensis could be
compared. During the 40-month study period, 90,246 traps were set on the university campus,
and another 48,818 set elsewhere in the country, for a total of 139,064 trapnights. This does not
include the effort made during the mark and release study done for 13 months on the campus
(Tang Christensen unpubl.).

 Examination of material-- Live animals were anesthetized with ether or chloroform, bled
by cardiac puncture, and brushed for ectoparasites, then examined as were the trap-killed
specimens. Head-body lengths (HBL) and tail lengths were always recorded, and often the ear
and hind foot lengths as well. Animals were weighed either by Pesola spring balances or a
Mettler automatic balance. Sex was determined. Females were examined externally to determine
perforation of the vagina, and teat number was occasionally recorded. Upon dissection the
uterus was examined for placental scars, and embryos present were counted for each limb of the
uterus. The crown-rump of one representative embryo of each litter was measured. Lactation,
when indicated by presence of turgid, milk-filled mammary glands, was noted. The male
reproductive status during the first 18 months of the study was recorded simply as scrotal or
abdominal testes. During the last two years, testes were examined for condition of the
epididymal tubules, these being recorded as visible or not. Initially, the presence of motile sperm
in the epididymal tubules was determined microscopically, until the correlation with visible
tubules was established. The weight of one testis was recorded for approximately 50 males per
month during the last 13 months of the study. Specimens of taxonomic value were prepared
either as round or flat skins, and skulls were saved. Approximately 50 individuals were
karyotyped from marrow smears, prepared two hours following injection IP with 0.05% colchicine
at 0.01 ml/g weight. Smears taken from the femur were immersed before drying in 0.75%
aquaeous KCI for 15 min, placed in Carnoy's fixative for 15 min, and air-dried. The smears were
stained immediately with 5% Giemsa at pH 7.2 for 20 min, washed in tap water and air-dried.
Prior to injection with colchicine, a sample of cardiac blood was obtained for electrophoresis.
Hemoglobin electrophoretic patterns were prepared by the Helena system for 150 P. natalensis
from the campus population, for comparison with samples from elsewhere in Tanzania. Data
were recorded on examination sheets and then transferred to keysort cards. Meteorological
records were obtained from the University Meterological Station for the period 1970-1985.

 Study areas.-- The campus of Sokoine University of Agriculture is located on the western
edge of Morogoro, Morogoro Region, Tanzania (0651'S, 37*38'E), at an elevation of 650 m on
the northern slope of the Uluguru Mountains. Very little of the original vegetation remains at
low elevations in the Uluguru Mountains or in their vicinity, and random deforestation continues
toward the peaks despite their designation as a forest reserve. Along the south edge of the
campus on the slopes of the mountain range is a belt of secondary forest which contains remnants