No abstract

Summary Satellite tracking of elephants was found to be a valuable tool despite numerous technical problems. A local reference beacon is vital for obtaining an adequate number of accurate locations. Two out of ten satellite transmitters failed within two months of deployment, but an average of one location per collar transmitter was obtained every 3.4 days for the period October 1987‐May 1988. The study was made in the wet season in northwestern Namibia. Seasonal home ranges of elephants as determined by satellite tracking were larger than recorded elsewhere in Africa (c. 5800‐8700km2). Elephants from Etosha National Park moved to within 20 km of the Angolan border, and elephants in the Kaokoveld moved across previous bioclimatic demarcations of populations. The validity of previous classifications of elephants into discrete populations in northwestern Namibia is questioned.

Post‐natal growth in the African elephant (Loxodonta africana) was described using three alternative mathematical models, and two age estimation schedules. Von Bertalanffy, Gompertz and Logistic equations all provided adequate models of post‐natal growth in a species for which age estimation methods are largely unsubstantiated. Gompertz and Logistic models overestimated pre‐weaning growth and underestimated adult size. Self‐accelerating growth is of short duration (one and three years in females and males, respectively), and we found no evidence of a secondary growth spurt in males. Males, nevertheless, continue to grow throughout their lifespan, while females reach asymptotic size at the age of 35–40 years. We found no evidence of differences in growth rate of males and females up to 10 years, and there does not seem to be differential investment in male and female offspring. Growth rates of captive elephants differ substantially from all wild populations studied and may not serve as adequate references for the revision of existing age estimation schedules.

Sexual differentiation of the Müllerian duct system and gonad in female fetuses conformed to the general mammalian pattern, whereas the external genital anlage in male and female fetuses developed into the male facies. Interstitial cells occurred in the primary germinal cords of both male and female fetal gonads and are suggested to be the source of androgen production in spotted hyaena fetuses. Maternal transfer of androgens to the fetus via the placenta was negligible. Male fetuses had higher gonadal and plasma concentrations of testosterone than female fetuses, and vice versa for androstenedione. Plasma testosterone was nearly as high in a female 31-day-old fetus as in the twin male, and masculinization of the genital tubercle probably results from an episode of androgen secretion by the fetal gonad although the Wolffian ducts in the female do not respond.

Low-level vertical changes in temperature and wind exert powerful and predictable influences on the area ensonified by animal vocalizations. Computer modelling of low-frequency sound propagation in measured atmospheric conditions predicts that the calls of the savanna elephant at these frequencies can have ranges exceeding 10 km and that the calls will be highly directional in the presence of wind shear. Calling area is maximized under temperature inversions with low wind speeds. Calling area changes substantially over 24 h periods; on any given day, the calling area undergoes an expansion and contraction which may be as large as one order of magnitude. This cycle is modulated by topography, regional weather patterns, seasonality and possibly by climate variation. Similar influences affect the somewhat higher-frequency calls of lions and may be a selective pressure towards their crepuscular and nocturnal calling behaviour. Coyotes and wolves, which also live in areas with strong and prevalent nocturnal temperature inversions, show similar calling patterns, maximizing their chances of being heard over the longest possible distances. The pronounced dawn and evening vocalization peaks in other animals including birds, frogs and insects may reflect the same influences in combination with other factors which selectively limit high-frequency sound propagation. Atmospheric conditions therefore need to be taken into account in many field studies of animal behaviour. A simplified method for estimating sound propagation during field studies is presented.