Social Cooperation
Large Aggregations and the Herd Effect
The wildebeest is a highly social ungulate that lives within large aggregations (Moss, 1975). Several interrelated factors cause the wildebeests to form large herds that can number in the thousands. First, the feeding patterns of the wildebeest permit them to clump together while feeding. Thus, attraction to a particularly nutrient-rich area plays a role in the tendency of wildebeests to aggregate in large herds. Secondly, wildebeests are naturally gregarious, and thus they appear to enjoy rubbing against one another or laying together with their backs touching. Finally, and perhaps most importantly, wildebeests aggregate together as an anti-predator tactic (Moss, 1975). Because the wildebeest is so large and easily visible to its prey, it is unable to hide from predators (Moss, 1975). While the wildebeest often acts aggressively in defense against smaller predators, fighting larger prey such as lions is impossible. Thus, the wildebeest employs the herd effect as its anti-predation strategy. As a member of a large group of dark gray animals, an individual greatly reduces his chances of being picked off by a predator on the prowl. The herd may even act aggressively against a predator by approaching as a united body so that the predator is unable to make an undetected move (Moss, 1975). The herd effect is especially important for young wildebeest calves, which do not lie out like other antelope species (Moss, 1975). Thus, the herd effect serves as the wildebeest's main form of social cooperation.
Synchronous birthing is another tactic used by the wildebeest to protect young from predation, and this measure can also be considered a form of social cooperation. Because almost all females deliver their young during the same two-week period early in the rainy season, the survival of the calves is higher than if the wildebeest delivered year round (Wittenberger, 1981). As mentioned previously, wildebeest herds can number into the hundreds of thousands. Thus, predators of the calves become overwhelmed by the number of new wildebeests and simply cannot pursue all of them at one time. As a result of this phenomenon, calves born before or after the main peak are captured by predators more frequently (Wittenberger, 1981). Because synchronous birthing increases the survival of young calves, synchronous birthing results in the wildebeest population from the process of natural selection (McFarland, 1982). Synchronous birthing, then affects other areas of the wildebeest social organization such as migration and habitat choice (McFarland, 1982).
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