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The Mating System of the Giraffe

Photograph courtesy of Dr. Case and used with her permission.

Sexual Maturation and Fighting

Giraffes reach sexual maturity when they are four years old (Nature-Wildlife, 2002).  Female giraffes have a calf about every two years as the gestation period is 14 months and she can't get pregnant for about 2 months after the birth of a calf because she is lactating (Moss, 1975).  Although male giraffes are sexually mature at the age of four, they do not begin to compete for mates until about age seven, because they must establish their position in the dominance hierarchy through necking contests (Anderson, 1982).  During a necking contest, the two males wrap their necks around each other and occasionally hit each other with their heads (Simmons, 1996; Van der Jeugd, 2000).  Older males are larger and also have stronger and heavier heads because bone continues to deposit on their head forming horns throughout adolescence (Simmons, 1996).  Serious fighting among male giraffes (bulls) is rare, but does occur when an estrus female is present (Anderson, 1985; Moss, 1975).  

Mating Behavior

Males must always divide their time between feeding and reproductive activities because giraffes don't have a specific breeding season (Ginnett, 1997). Male giraffes wander from herd to herd testing the females to see if they are in estrus (Moss, 1975).  The male approaches a female and nudges and licks her to induce her to urinate.  Then he licks some of the urine, raises his head, and curls his lips (Moss, 1975).  Through this "flemen" behavior which is common in ungulates, the male is somehow able to assess, through smell and taste, whether or not the female is in estrus (Moss, 1975).  The dominant or alpha male exerts his dominance over the other males before the females are ready to mate and thus is able to do most of the mating with the females (Simmons, 1996).  Multiple male giraffes can perform the "flemen" behavior on the same female, but only the dominant male mates with the female (Moss, 1975). If the female is not in estrus, then the male will move on and test another female, but if the female is in estrus, the male will follow her, leaning against her and nosing her (Nature-Wildlife, 2002). Initially, the female moves away from the male, but eventually the female allows the male to mount her multiple times (Moss, 1975). Mejia believes that there is some pair-bonding formed during mating, but other researchers do not believe that this is the case (Moss, 1975).

Why hierarchical promiscuity?

Mating systems are based on female choice and social behavior, because the female has a larger investment in the offspring. Females attempt to find a mate with high fitness levels while males behave to maximize their fitness (Wittenberger, 1980). Thus males compete for the females and different mating systems arise depending on female dispersion. Males prefer harem polygyny so they can exclusively mate with females, but if the size of the female group increases, one male is not able to defend all of the females and thus multiple males will defend the females forming a hierarchical promiscuity mating system (Wittenberger, 1980). Therefore, hierarchical promiscuity is observed in giraffes because female groups can be large, female homeranges are much to large for one male to control, and the location of females at any point in time is not predictable. Also, it is not possible for males to predict which females are in estrus until they use the "flemen" behavior since females go into estrus at various times (Ginnett, 1997). Thus, multiple males associate with female groups and compete for mating rights through their dominance hierarchy (Moss, 1975). The alpha or most dominant male has the greatest mating success over time, but other high ranking males also have the opportunity to mate with females. No bonds are formed between males and females in this mating system (Van der Jeugd, 2000).