The insectivorous bat under review, Otomops martiensseni (Matschie) is essentially an African bat with a distribution from down south to as far north as Kenya. It is cave-dwelling and does not appear to occur in West Africa. In this study, reproduction of two populations, one at Suswa in the Rift Valley, latitude 1°5′S and the other at Ithundu in the Chyulu Hills, latitude 2°30′S was investigated and compared. Regular monthly samples from both populations were collected commencing in March 1970 and running on to February 1972. The bats were processed in the laboratory for pregnancies, weights of testes and foetuses and other measurements and observations. Seasonality in the occurrence of pregnancies was observed in both populations, that is, from October to January only. Also the adult males realized a peak in their mean testicular weight in August, a short period just before the onset of pregnancies thus indicating the most likely time of mating. The female sexual cycle at Ithundu appears to be geared to the rainfall regime as measured at Makindu Meteorological Station about 10 km away. The male sexual cycle, on the other hand, shows a peak in the very dry months suggesting that such a dry spell may be more important than the rain. Molossid bats exhibit variation in their breeding cycles.
The breeding cycles of two populations of the cave dwelling insectivorous bat, O. martiensseni have been elucidated. In one population at Ithundu, the adult females show evidence of pregnancies from October to January and the adult males exhibit a peak in their sexual cycle in August. In the Suswa population, a similar state of affairs obtains. In both populations, there is the curious tendency for pregnancies to occur also in May at Suswa and Ithundu; and also in June in Ithundu. But as such pregnancies are not sustained in the ensuing months and are of extremely low magnitude, they cannot be regarded as constituting another breeding season. The peak in the adult male cycle occurred during the dry spell from June to September. The peak in pregnancies at Ithundu appears to coincide with the peak rainfall and it is possible that the same is true of Suswa. Considering that these bats are seasonal in their breeding and that they are only monotocous, their recruitment rate as shown by their age distribution is low.