DISPERSAL STATUS INFLUENCES HORMONES AND BEHAVIOR IN THE MALE SPOTTEDHYENA

Male spotted hyenas (Crocuta crocuta) reach puberty at 24 months of ag e and then invariably emigrate from their natal clans 1 to 38 months l ater. Thus there are two classes of reproductively mature males in eve ry Crocuta dan: adult natal males born in the dan and adult immigrant males born elsewhere. In one free-living hyena population in Kenya, th ese two groups of males were compared with respect to measures of aggr ession, social dominance, sexual behavior, and circulating hormone lev els. Adult natal males engaged in higher hourly rates of aggression th an did immigrants, won all fights with immigrants, and were socially d ominant to immigrants. In addition, adult natal males engaged in far l ower hourly rates of sexual behavior with resident females than did im migrants, and natal males were never observed to copulate with natal f emales. Mean basal plasma cortisol values did not differ between the t wo groups of adult males, but cortisol concentrations in immigrants we re positively correlated with tenure in the dan and with immigrant mal e social rank. Adult natal males had plasma testosterone levels signif icantly lower than those of immigrants. Social rank and plasma testost erone values were positively correlated among immigrant males. Thus tw o different relationships appear to exist between circulating testoste rone and social rank in male Crocuta: one apparent in immigrants and t he other in natal adult males. Our results suggest that dispersal migh t disinhibit testosterone secretion in postpubertal male hyenas. (C) 1 998 Academic Press.