The Mating System

Wildebeest photo courtesy of Dr. Verna Case

Why Lek-promiscuity?

The wildebeest mating system can be classified as lek promiscuity.  In the wildebeest mating system of lek promiscuity, a territorial male defends a patch of ground and competes for dominance (McFarland, 1982).  As described in the discussion of wildebeest social organization, these territories do not contain attractive resources for the females.  Rather, these areas are often bare patches of ground, which measures a few meters in diameter at the most (McFarland, 1982).  

During the breeding season, female wildebeests pass through the lek in order to mate (Moss, 1975).  When females pass through, territorial behavior increases dramatically.  Herding, courting, and challenging take place constantly at a loud, high pitch.  Male wildebeests may become so excited that they begin to foam at the mouth, make pelvic thrusts, and spontaneously ejaculate (Moss, 1975). They attempt to gather as many females as possible onto their territories and in so doing, fragment the larger herd of females into smaller units.  Each of these smaller aggregations of females is guarded by one bull, and generally only one female in the group is actually in estrus.  The territory-holding bull then attempts to court the estrus female.  He holds his head out, utters a deep grunt, follows the female until she will stand for him, mounts her, and then copulates.  All of this activity occurs within a few seconds (Moss, 1975).  If the female cooperates with the male's intentions, the bull may mount her several times within the next few minutes.  The female may then continue to move through other territories and mate with other bulls (Moss, 1975).  If the female being pursued will not stand for the bull, the male may circle in front of her and "rear up before her with a full erection in a dramatic copulatory display" (Estes, 1968).    A female will come into estrus around sixteen months of age, but not every female will give birth the first year depending on weather conditions (Moss, 1975).  Eight months after the mating season, a female births one calf (Gnu, 1968).  If good conditions exist, a female can give birth each year for her entire lifespan (Moss, 1975).  

Because harem mating systems require that males defend females, even if for a short period of time, the wildebeest does not exhibit this type of system.  Two major factors prevent harems from predominating wildebeest life. First, females may aggregate into herds of up to 150 wildebeests (Owen-Smith, 1977).  Due to energy requirements and practicality, this large number precludes male territory holders from containing and defending a select group of females on their territory. Second, because females graze and roam over a large spatial area throughout the plains, males are even less likely to be able to gather together and defend a small group of females.  Thus, the male wildebeest relies on lek promiscuity and must gain a territory in order to mate. 

Although many other antelope species do not breed during a highly restricted period of time, the wildebeest mate within a short time span after the rains.  This short span of mating occurs when the wildebeest are in good shape and results in a birthing season during the rainy season on the plains.  This timing works out well for the young calves, who are quickly able to find tender grass to eat (Moss, 1975).  Thus, because of the restricted mating season, approximately 80% of calves are born during a two to three week period.  This phenomenon is known as synchronous birthing as acts primarily as an anti-predator device (Moss, 1975). 

A female wildebeest does not give birth alone as do many other antelope species.  The female, instead, delivers her newborn calf in the middle of the herd (Moss, 1975).  Researches in Ngorongoro found a regular calving ground where more than twelve females would deliver their calves during on day (Moss, 1975).  Usually calves are born in the morning so that the young ones can spend the day learning to recognize their mothers, gaining strength, and practicing running (Gnu, 1968).  These activities must occur before nightfall, which lurks with the dangers of hungry hyenas (Gnu, 1968).  Until the head of the calf appears, females are consciously able to forestall birth so as to avoid predation.  A female lies on her side to give birth.  Immediately after the calf is born, the female leaps up and turns toward the calf.  She licks him and removes the fetal sac.  Such behavior is incredible important so that the calf is able to recognize its mother and avoid losing her during herd movement.  After approximately three to seven minutes, the calf is able to stand, nurse, and even run with its mother.  Calves must remain close to their mothers so as to prevent separation.  Unfortunately, a large percentage of wildebeest calves loose sight of their mothers each year and become dinner for the always hungry hyena (Moss, 1975).  Many young wildebeests also lose their lives to disease (Gnu, 1968).  Some catch a virus known as "yearling disease" before they reach one year of age.  Due to disease, predation, and separation from their mothers, only one out of every five wildebeests survives the first year of life (Gnu, 1968). 

Good-byes to the Yearlings

The Male's Story:  The territorial males in the area separate male yearlings from their mothers and their herds.  At approximately seven or eight months of age, calves are weaned.  During the weaning process, young males gather together (possibly along with some young females) in order to form bachelor herds.  By nine to ten months of age, a small proportion of young males join a bachelor herd that associates with a female aggregation.  The majority of young males remain attached to their mothers until the mothers give birth the following season.  At the birth of the next calf, the previous year's calf is driven away from his mother.  This separation occurs as a result of the yearling's own behavior.  The yearling will persistently attempt to remain in close contact with his mother.  Since a mother will not tolerate anything that comes between her and her newborn calf, the yearling is rejected with emphasis from his mother.  Additionally, the distressed behavior of the newly separated calf evokes aggressive behaviors from the male who owns the particular territory on which the calf is located.  This male escalates the separation process by chasing the yearling repeatedly until the yearling gives up and leaves his mother. If the mother is unable to give birth or loses the new calf, the yearling is permitted to stay longer with his mother.  The female will even continue to allow the yearling to suckle (Estes, 1968). 

The Female's Story: Estes found that some females may be able to join their mothers' herds.  However, many of the young females end up among strangers because they stay further from these wildebeests and thus elicit less aggression from them (Estes, 1968).  Other research indicates that females may stay with their mothers longer.  If these females do stay longer, there may be some degree of relatedness within the female herds ö especially the sedentary populations (Moss, 1975).  More research in this area is needed before the female relationships can be completely understood.

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