A PRELIMINARY INVESTIGATION OF URINARY TESTOSTERONE AND CORTISOL-LEVELS IN WILD MALE MOUNTAIN GORILLAS

Urinary steroid hormone levels were measured in wild male mountain gor illas (Gorilla gorilla beringei) to determine how levels of testostero ne and cortisol corresponded with age and social rank. Urine samples w ere collected noninvasively from 18 males, ranging in age from 3-26 ye ars, in three groups of wild mountain gorillas at the Karisoke Researc h Center, Rwanda, Africa, and samples were analyzed using radioimmunoa ssay procedures. Males were classified as being immature (<7 years), m aturing (10-13 years), or adult (+13 years of age). Immature males had significantly lower levels of testosterone and higher levels of corti sol than both maturing and adult males. No differences in testosterone or cortisol levels were found between maturing and adult males. Domin ant males exhibited a trend toward significantly higher levels of test osterone than subordinate males, but no difference was found between c ortisol levels of dominant and subordinate males. These results sugges t that the increase in testosterone associated with puberty occurs pri or to any outward sign of development of secondary sexual characterist ics. Within-group male-male competition may affect testosterone levels , but the lack of difference in cortisol levels between dominant and s ubordinate males suggests that subordinate males are not socially stre ssed, at least as measured by cortisol. (C) 1997 Wiley-Liss, Inc.