III. The Reproductive Processes of Certain mammals *— Parts IV and V. Part IV. The oestrous cycle of the grey squirrel (Sciurus carolinensis)

Abstract

Although, it is abundant in many parts of England and of economic importance, singularly little seems to be known about the breeding habits of the grey squirrel (Sciurus carolinensis).Middleton (1930) noted that 23 females examined in March and April, 1930, were non-pregnant, although the males were sexually active. Records of litter size quoted by Middleton suggest that four to six is usual. Apparently no true hibernation occurs in the grey squirrel and this species appeared to be very suitable for the extension of oestrous cycle work. Collection of field material was started in October, 1930. In view of the obvious limitations of such material, attempts were immediately made to induce the animals to breed in the laboratory. These were unsuccessful and although some few animals showed signs of approaching oestrus, no pregnancy or ovulation was obtained. Since better quarters are now available, it is hoped that further information may be secured by observation of animals breeding under laboratory conditions. Such information would relate mainly to the time relations of the cycle and to the nature of the changes in the absence of mating.