Reproduction, Growth, and Mortality of the Vespertilionid Bat, Eptesicus fuscus, in Kansas

A study was conducted on reproduction, growth, and mortality of Eptesicus fuscus in an area of central Kansas where morphological intergradation has been demonstrated between distinctive eastern and western forms. Observations were made on reproductive chronology and the hypothesis was tested that sexual size dimorphism is evident throughout the period of growth. The parturition period was from late May through the middle of June with most young born in the first week of June. Although the number of implanted embryos exceeded the number surviving to birth, the litter size was two. No significant differences in size or weight were evident between males and females in the prenatal period. Postnatal growth rates in linear dimensions were greater for females than for males. Young bats were foraging at the age of 4 weeks by which time the forearm length had reached 86 and 89 per cent of adult size for males and females, respectively. Adult linear size was attained in approximately 70 days. At birth young bats averaged 3.14 grams or approximately 16 per cent of the postpartum weight of females. Weight gains were nearly linear for the first 6 weeks in both sexes. No sex differences in body weight were evident until young bats were weaned, but after this time females gained weight faster than males. Embryonic resorption, accidents, and predation are considered as factors influencing mortality.