Social Organization
African buffalo live in very large herds. The number of individuals in a herd changes throughout the year depending on the season. The rainy season is usually the height in mating activity (because of the abundance of nutrients available for females) and this is when the herd size is normally the greatest. The average herd has a couple hundred individuals however they can swell to as large as 1000 individuals (Dalquest 1965).
Photo courtesy of Dr. Kay E. Holekamp
Herd Splitting
The African buffalo herds undergo a process of herd splitting every year. During the dry season the male buffalo migrate away from the herd and form bachelor groups (Turner 2005). There are two types of bachelor groups that form. The first is a group of males who are between the ages of 4 and 7 years old (Ryan 2006). These males leave the group and form subgroups of about 3-4 individuals (Newell 2000). This ensures a greater chance of finding sufficient food to survive out the dry season and, because it is no longer mating season, it is not necessary for the males to remain around the females (Turner 2005). The second type of bachelor group is made up of individuals that are 12 years and older (Ryan 2006). These males are actually smaller than the full grown males because their body weight declines because their teeth become worn out after years of rumination (Ryan 2006). These older males often leave the herd and never return. They do this because they are no longer able to compete with the younger, more aggressive males for reproduction and because they can avoid unwanted fights and agonistic behavior from other males. They are also no longer required to go on long migratory grazing trips. These older buffalo do not change their habitat or vegetation however they no longer continue to behave as efficiently as they did when they were younger (Sinclair 1977). During the wet season the males return to the herd so that they can mate with the females. They stay throughout the season so that they can offer their protection since predation rates are higher and there are many calves during this time of the year (Main 1990).
Dominance
Males exist within a linear hierarchy. About 10-15% of the males in the herd have dominance and this is based on their age and size. These males perform most of the copulations with the females. The sub adult males form their own subordinate groups and they stay with the herd because they are protected and because they have a chance of becoming dominant in a few years when they are bigger, strong, and more aggressive. The dominant males are also dependent on the sub adults staying because they are safer when the herd is larger and so sub adult copulation is sometimes tolerated (Turner 2005).
Family Unit The large herd is a stable family unit. It has been observed that herds sometimes mix and mingle however they can immediately recognize members of their own herd among the other buffalo. The only family unit within the herd is the mother-calf unit (Newell 2000). Females have their first calf at the age of 4 with the gestation period lasting almost a year (Ryan 2006). They give birth to only one calf. The mother and the calf share an unusually strong bond that lasts until the calf matures and gives birth to her own and sometimes even longer (Newell 2000). This bond is strengthened because the males leave the herd each year and so care giving falls completely on the mother. |
Photo courtesy of Eva Hejda |
Altruistic Behavior
Many studies have attempted to examine the strange phenomena of group altruism. The African buffalo are a group that exhibits altruistic behaviors, many times when an individual is abandoned or attacked. If altruistic behavior is approached from a group selection stand point (the belief that group selection favors traits that increase the fitness of groups relative to other groups) then groups of altruists are more fit than groups of nonaltruists. An interesting example of African buffalo altruistic behavior can be seen in the adults females' "voting behavior." This occurs during times of rest and when all buffalo are sitting on the ground. The females will stand at will, shuffle around, and then sit back down. The direction in which they sit, signals the direction in which they think the herd should move. This continues for about an hour. At the end of the "voting" process the entire herd stands and moves in the same direction. This represents a sense of communal decision making, there is no hierarchical decision and dominance plays no role, the group moves in the direction that is decided on by the group (Wilson 1997).