Comparative Analysis of Gonadal and Adrenal Activity in the Black and White Rhinoceros in North America by

Patterns of fecal reproductive steroid metabolites and adrenal corticoids were characterized for 12- to 24-month periods in black (n = 10 male, 16 female) and white (n = 6 male, 13 female) rhinoceroses at 14 institutions. All black rhinoc-eros females exhibited at least some ovarian cyclicity on the basis of fecal progestogen analysis (range, 2–12 cycles/yr). However, cycles often were er-ratic, with many being shorter (<20 days; 18 % of cycles) or longer (>32 days; 21%) than the average of 26.8 – 0.5 days (n = 104 cycles). Five females exhib-ited periods of acyclicity of 2–10-month duration that were unrelated to season. One complete and seven partial pregnancies were evaluated in the black rhinoc-eros. Fecal progestogens increased over luteal phase concentrations after 3 months of gestation. Females resumed cyclicity within 3 months postpartum, before calves were weaned (n = 5). Approximately half of white rhinoceros females (6 of 13) showed no evidence of ovarian cyclicity. Of the cycles observed, 5 were “short” (32.8 – 1.2 days) and 24 were “long ” (70.1 – 1.6 days). Only two females cycled continuously throughout the study. One had both long (n = 9) and short (n = 2