Abstract
Environmental variables strongly influence reproduction in squirrels living in temperate zones where winter is a highly inclement period. However, even in tropical (Emmons, 1975) and subtropical squirrels (Viljoen, 1975), breeding is seasonally related to the environment. No single environmental factor exerts complete control over reproductive activity; for example, changes in light regime are accompanied by alterations in other environmental influences. Nutrition, inclement weather, rainfall and photoperiod are interrelated variables that have all been mentioned as factors affecting sciurid breeding seasons. Little experimental work has been done, however, and when discussing these factors separately, one must keep in mind that they do not stand in isolation. Some examples of the complexity of environmental influences on breeding patterns are evident from studies on the bush squirrel, Paraxerus cepapi cepapi, at Naboomspruit (24°35′ S, 28°47′ E) in South Africa (Viljoen, 1975). Rainfall commences in September, and the first females come into oestrus soon after. At this time, which coincides with or is just slightly after the spring equinox, there is a green flush of vegetation and flowers are abundant. In the male of this species the scrota show a sharp increase in size in June just before the winter solstice, when temperatures are at their lowest and rainfall is at a minimum. This coincides with the end of the period of food abundance. Scrotal shrinkage is apparent in late December and January during the rainy season, when maximum temperatures are at their highest and just after day-length has started to decrease. The number of vesicular follicles per ovary is low from April to August (1.3 ± 1.6 in May, n = 6) and much higher from September to December (22.8 ± 3.3 in September, n = 3). Corpora atretica show a reverse trend. Therefore, in South Africa, the seasonal availability of food has probably influenced the evolution of breeding periods in tree squirrels, but this factor is not easily separated from rainfall and day-length.
Mrs S. Viljoen is currently studying eco-ethology of Southern African tree squirrels for a doctoral degree at the University of Pretoria, South Africa. After attaining the M.Sc. degree in Zoology at the same institution, she spent one year as a research fellow of the Mammal Research Institute, working on olfactory communication of small mammals.
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Viljoen, S. (1981). Environment and reproduction in tree squirrels with special reference to the genus Paraxerus. In: Gilmore, D., Cook, B. (eds) Environmental Factors in Mammal Reproduction. Biology and Environment. Palgrave Macmillan, London. https://doi.org/10.1007/978-1-349-03964-7_12
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DOI: https://doi.org/10.1007/978-1-349-03964-7_12
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