BULLETIN FLORIDA STATE MUSEUM VOL 34(6)


from a catch of 170 mice in December 1931, to 20 in January 1932." This
reduction in catch by 88 percent compares well with the grid estimate of
December 1983 of 769/ha which dropped to 56/ha. in January 1984, a decline
of 93 percent. Harris attributed the rodent "plague" of 1930-32, with peak
abundance in 1931, to migration of rodents into the Morogoro area from
Kimamba, over 40 miles to the east, rather than to a result of "an abnormal
increase of the local population." Without more detail of his sampling
procedures, this conclusion is arguable. As closely as the university campus
population was monitored during the 40-month period, there was no
suggestion during 1982-83 that numbers were "explosively" increasing, although
abundance was clearly higher following the 1982 short rains, and off-season
breeding occurred in January 1983. The less than obvious rise to "crash" level
through the influence of higher precipitation level on food and cover, with
increased survival and extended reproductive period, is a simpler and more
likely explanation of high density than is migration from distant populations.

 Implications for control.-- Given the high cost to a fragile economy of
comprehensive rodent control programs, it is essential that control be rational
to achieve maximum benefit for both agriculture and public health. An
attempt to significantly decrease rodent numbers during the post-harvest
period when maximum density is reached is far less effective and considerably
more expensive than it would be to take preventive measures when populations
are at minimum density. As this coincides with the pre-reproductive period in
Morogoro, from January to April (disregarding off-season breeding in years of
excessive rainfall), each rodent removed from the breeding population
represents a far more significant result than one removed following harvest,
because of the very real possibility that an individual female can produce 50
offspring between April and September. By concentrating rodent control
activities in fields between January and the onset of the long rains in April,
limited resources will have maximum effect, and both germination and harvest
success should be improved. Coupled with encouraging farmers to clear away
stubble immediately after harvest and improvement of grain storage structures,
as pointed out by Harris a half-century ago, effective rodent control could be
realized. Systematic sampling programs in climatically differing areas can
indicate proper timing for rodenticide application, i.e. in the period
immediately preceding onset of the main reproductive period, probably
predictable by close study of rainfall patterns.