262 TELFORD: MULTIMAMMATE RAT POPULATION BIOLOGY IN TANZANIA


given by De Witt (1972) of a longevity in the wild of 339 days for P. natalensis
in South Africa. The main reproductive season begins in April of each year,
when female young of the preceding season appear with perforate vaginae
(Fig. 10).
 The first litter is born in late April or early to mid-May, followed by
another three litters at approximately monthly intervals, with reproduction
ending in August (Fig. 11). It is possible that some females could produce
more than four litters in those years when conditions favor reproduction from
January onward, but survival of a given female through the entire season is
probably unlikely. Very few, if any, young are born from September through
December in field situations, but reproduction is apparently continuous in
Morogoro Region among those P. natalensis inhabiting houses or other
structures where food and cover are available.
 Females produce, on the average, 11.7 embryos per litter, with a range of
3-23 seen in utero (Table 1). Females may show as many as 24 teats. Those
females smaller than 105 mm HBL appear to produce 1-2 embryos fewer than
those 105 mm and larger. Maximum litter size was seen in the females which
were 120-129 mm HBL, averaging 12.0-12.6, while in the largest and probably
oldest females, those over 129 mm HBL, slightly smaller litters were found,
averaging 11.8 (Table 1).
 Little annual variation was seen in mean litter size compared with female
HBL, except in 1983 when females of 115-119 mm produced two more
embryos per litter than in the previous year (Table 2).
 A comparison of mean litter size with embryo size indicates that perhaps
two embryos are lost during gestation, with the number actually born probably
averaging around 10.6 per litter (Table 3).
 Maximum litter size occurs from May through July; early and late season
litters are 1-2 embryos fewer (Table 4).
 Embryo resorption in 1982 and 1983 was highest in August, but in 1984
when reproduction was continuous from February through August, resorbing
embryos were seen in each month at similar levels (Table 5). In terms of the
total number of embryos produced by the females examined, the proportion
resorbed was only 0.4-3.2 percent.
 Reproduction appeared to be more frenzied in 1982, when the population
was recovering from very low density probably caused by the severe drought in
preceding months. Females with either large or small embryos could be found
simultaneously lactating, implying that another litter was started immediately
after parturition (Table 6). In 1983 no females with embryos over 25 mm
showed lactation. The proportion of females with small embryos that were
also lactating decreased significantly in 1984, the year when reproduction was
continuous from February through August.