Sexual Behavior. Baboons breed year-round, though some populations show peaks in mating and births at certain times of the year. Copulations are concentrated during a short period of sexual activity called estrus (Beach 1976), which occurs cyclically and is signaled by large sexual swellings on a female’s posterior that correspond to the period around ovulation (Hendrickx and Kraemer 1969; Saayman 1970, 1972, 1973, 1975; Wildt et al 1977; Wallis 1983). In captive chacma baboons, artificially exaggerated swellings increased male sexual arousal, showing that swellings function proximately to attract males (Bielert and Anderson 1985; Girolami and Bielert 1987). Copulations may be initiated by either sex; females often initiate copulations via a sexual present in which they orient the perineum towards the male and pause with the tail lifted (Ransom 1981).
In multi-male groups of baboons, males and females form sexual consortships, which are relationships that are characterized by close proximity, increased grooming, and frequent copulation (Seyfarth 1978a; Ransom 1981; Rasmussen 1983, 1985, 1986; Bercovitch 1983, 1991, 1995). Consortship duration is largely related to the ability of a male to monopolize a female, which may in turn be related to factors such as the number of females in a troop simultaneously in estrus and alternative male strategies such as coalitions (see section on Reproductive Strategies of Male Baboons). Lengthy consortships are most common in chacma baboons, in which alpha males can monopolize estrous females for several days.
Many baboons give copulation calls, which are loud, distinctive vocalizations given by females during and/or after copulation (Hall 1962b; Saayman 1970; Boese 1973; Hamilton and Arrowood 1978, Collins 1981; Ransom 1981; Bercovitch 1985; O'Connell and Cowlishaw 1994; Semple 2001, Semple et al 2002; Maestripieri et al 2005; Swedell and Saunders 2006). These calls have been described as “intermittent roars” (Bolwig 1959), “staccato grunts” (Saayman 1970), and “gurgling growls” (Hall 1962b). Females give copulation calls while defecating as well (Hall 1962b; Boese 1973; Bercovitch 1985), suggesting that they may be an involuntary reaction to compression of the vaginal wall.
Reproductive Parameters. Menstrual cycles in baboons are typically 30 to 40 days in length, with the sexual swelling (estrus) component of the cycle usually lasting from 10 to 19 days (Hendrickx and Kraemer 1969; Bercovitch 1991). Pregnancy lasts from 165 to 185 days. The skin on the sides of the hips, next to the ischial callosities, usually reddens during pregnancy (Altmann 1970). Inter-birth intervals, i.e., the length of time between surviving infants, can last anywhere from 12 to 40 months. Virtually all female reproductive parameters respond to changes in local environmental conditions: age at menarche, interbirth intervals, infant growth rates, and infant survival all vary with food supply (Bercovitch and Strum 1993; Lycett et al 1998; Gauthier 1999; Altmann and Alberts 2003b; Barrett et al 2006; Higham et al 2009b), interbirth intervals vary with mean annual temperature (Hill et al 2000), and extreme heat or drought reduces female fertility (Beehner et al 2006c).
Life History. Male baboons reach adult size at around 10 years of age, with an adolescent growth spurt just prior to reaching adult body size (Altmann et al 1981; Sigg et al 1982). Females typically reach reproductive maturity between 4 and 5 years of age in the wild and at least a year earlier in captivity, and give birth to their first surviving infant at between 5 and 7 years of age (Altmann et al 1977, 1981; Hadidian and Bernstein 1979; Scott 1984; Smuts and Nicolson 1989). Females reach adult body size at between 5 and 6 years of age (Altmann et al 1981; Sigg et al 1982).
Content contributed by:
Dr Larissa Swedell
|Thanks to the following reviewers:
Dr Susan Alberts
Dr Cliff Jolly
photographs M. Pines (hamadryas male grooming female) and L. Swedell (chacma female walking with infant)
For a more scholarly version of the information on these pages, see:
Swedell, L (2011) African Papionins: Diversity of Social Organization and Ecological Flexibility. IN Primates in Perspective, Second Edition (Campbell CJ, Fuentes A, MacKinnon KC, Bearder SK, Stumpf, RM, eds). New York: Oxford University Press, pp. 241-277.
When using information on these pages, please cite the URL of the specific page from which you acquired the information. For scholarly citations of this material, please cite the above chapter by L. Swedell, available as a pdf by emailing the author. Please credit either this website or the above chapter for any and all use of this material.