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The Northern White Rhinoceros Ceratotherium simum cottoni is a subspecies of the White Rhino that is almost extinct in the wild. We studied the last reproducing herd kept in Zoo Dvur Kralove to describe its vocal repertoire. The calls produced by eight individuals were recorded and analysed as concerned both sound properties and behavioural contexts in which they were emitted. We distinguished 11 calls belonging to four categories: (1) tonal harmonic sounds, (2) puffing sounds, (3) growling sounds, and (4) repetitive sounds. We found an apparent similarity between acoustic parameters of homologous calls recorded in both white rhino subspecies. We further confirmed that the repertoire of white rhino calls is much larger than that reported in other rhino species. We tentatively interpret this finding as an adaptation to increased sociality. Four calls reach the infrasound range; nevertheless, they are probably not used for communication over distance. This is obvious in the case of the grouch call, which contains the highest infrasound component. There are, however, other candidates for such a communication function: the repetitive pant sound, which is not known in other rhino species. We hypothesise that the repetitions may enhance their audibility in the typical open habitats of white rhinos.

The metabolism and excretion of progesterone in different animal species results in several fecal 5‐reduced progesterone metabolites (pregnanes), which in recent studies were quantified using progesterone antibodies. To increase the accuracy of fecal 20‐oxo‐pregnane evaluations in the black rhinoceros, enzyme immunoassays (EIA) using antibodies against 5α‐pregnane‐3β‐ol‐20‐one 3HS:BSA (5α‐20‐one EIA) and 5β‐pregnane‐3α‐ol‐20‐one 3HS:BSA (5β‐20‐one EIA) were developed. The assays showed high crossreactivities with pregnanes containing a 20‐oxo group and are referred to as group‐specific; results of these assays were compared with an EIA using an antibody against 6HS‐progesterone (4‐ene‐20‐one EIA). Fecal samples of both subspecies of the black rhinoceros (Diceros bicornis michaeli, n = 5, and Diceros bicornis minor, n = 1) during pregnancy were collected 1–3 times/week. HPLC separation showed three major immunoreactive fecal 20‐oxo‐pregnane peaks; their elution profiles and different crossreactivities in the three EIAs provided strong evidence that these peaks are 5α‐pregnane‐3, 20‐dione, 5α‐pregnane‐3α‐ol‐20‐one, and 5α‐pregnane‐3β‐ol‐20‐one. Pregnane values in the pregnant animals continuously increased between months 3–7 and were significantly (P < 0.01) elevated above the levels of nonpregnant animals (0.2 μg/g) by week 11. During months 6–13 concentrations in the 5α‐20‐one and in the 5β‐20‐one EIA (5–11 μg/g) were significantly (P < 0.01) higher than in the 4‐ene‐20‐one EIA (1.5–3 μg/g). In conclusion, the immunoreactive fecal 20‐oxo‐pregnane metabolites in the black rhinoceros are determined more accurately with antibodies against pregnane‐20‐one‐C3 conjugates, as compared with a progesterone antibody. © 1996 Wiley‐Liss, Inc.