Social organization

Bovidae exhibit a range of sociality in their grouping behavior. Some species are solitary or near solitary, such as the bongo and dik-diks (Madoqua) of Africa. Species at this end of the group size spectrum are often territorial, living alone or in groups of two to three animals, usually in closed forests and dense shrublands. In other species, the basic unit of two to three is similar, but larger temporary groups form at certain periods in the year. Some, like klipspringer (Oreotragus oreotragus), live as mated pairs for most of the year. Bovids living in open habitats almost always occur in medium to large sexually segregated groups, with adult males living separately from females and young for most of the year. Group size across the whole spectrum appears to be dependent more strongly on habitat structure than on characteristics of the species; the larger groups are more commonly encountered in open habitats such as grasslands and savannas, and smaller groups in dense forests where visibility and, consequently, group cohesion are reduced. The largest bovid groups have been recorded in North American plains bison in the early nineteenth century, and today, the largest to be seen are the migratory herds of blue wildebeest (Connochaetes taurinus) in the Serengeti of Tanzania. In both cases, these "supergroups" were comprised of several thousands of individuals, probably comprised of smaller, more stable units, although group membership can be quite fluid. The primary benefit of living in groups is reduced predation due to dilution (decreased probability of being killed) and to increased vigilance (many eyes to detect predators).

Several species of Bovidae, particularly many of the African antelopes, are territorial, either defending territories year-round or only during the mating season. Other bovids occupy undefended home ranges that are, for the most part, used from year to year. Year-round territoriality can occur in any species inhabiting areas with relatively predictable, high-quality food supplies that are economically worth defending. This behavior is found in small forest-dwelling bovids such as the Cephalophinae and dwarf antelopes, as well as in larger African species such as the various kobs and reedbucks (Re-dunca). In species holding territories for reproductive purposes, the male owner most often advertises his presence by making himself conspicuous, for example, by standing on a high point of ground (e.g., topi, Damaliscus lunatus), and often marks points on the boundary using secretions of glands such as the antorbital gland just in front of the eye, or with dung and urine.

Social behavior

Bovids are generally highly social ungulates with a range of communication systems and displays. Many are vocal, with vocalizations ranging from the lion-like roaring of plains bison (Bison bison) to grunts, snorts, whistles, and barks. When on the move, an almost constant, relatively quiet grunting is

Bongos (Boocercus euryceros) inhabit the lowland rainforest of West Africa and the Congo Basin to Central African Republic and southern Sudan. (Photo by David M. Maylen III. Reproduced by permission.)

typical of the large-herd-forming species such as bison and wildebeest.

Bovid horn structure is closely related to fighting style. Horn size and shape vary and are grouped into four types. The relatively short, smooth, sharp-pointed horns of species such as duikers (Cephalophus) and North American mountain goat (Oreamnos americanus) are used for jabbing. These are the most dangerous horn types; the smoothness and sharpness mean that they are capable of inflicting lethal wounds. Species having such horns attempt to avoid unnecessary physical contact and rely more heavily on threat displays. Two other horn types are the heavily ridged and twisted forms found in impala (Aepyceros melampus) and blackbuck (Antilope cervicapra), and the relatively long, curved and relatively slender, ridged horns of oryx (Oryx) and sable antelope (Hippo-tragus niger); both these horn types are used for head-to-head wrestling. The ridges and twisted shapes help catch and hold an opponent's horns, and the combatants wrestle in an attempt to twist the opponent off balance and allow them to stab with the horn points. The fourth type is the relatively massive, solid horns of species such as African buffalo (Syncerus caffer) and bighorn sheep (Ovis canadensis), which are employed to butt heads. Species with this style use their horns like clubs, and sheep and goats often increase the force of the blow either by running at each other, standing on the hind legs and then dropping into the clash, or, in some cases, using the advantage of higher ground. Fighting with con-specifics for status, territory, or mates is the primary function

The African, or Cape, buffalo (Syncerus caffei) can spend over ten hours a day eating. (Photo by Rudi van Aarde. Reproduced by permission.)

of horns, but they can occasionally be used secondarily in defense against predators.

Displays are used by many animals, including bovids, to communicate in a range of social interactions. Lateral displays are common in many Bovidae, and often emphasized by adaptations that enhance the size (real and apparent) of the lateral profile. In the American bison (Bison bison) and gaur (Bos gaurus), the thoracic spines are elongated, permanently increasing the dimensions of their body profile. Other morphological adaptations that enlarge the lateral profile include dewlaps, the flap of skin hanging from the neck and chest of eland (Taurotragus oryx) and the zebu breed of domestic cattle (Bos taurus), and manes of long hairs. In greater kudu (Tragelaphus strepsiceros) and urial sheep (Ovis vignei), for example, the mane falls from the underside of the neck, and in nyala (Tragelaphus angasii), it extends along the underside of the belly as well. A temporary increase in lateral profile is achieved in some species such as the roan antelope (Hippotragus equinus) and chamois (Rupicapra rupicapra). They have a narrow band of long guard hairs running over the shoulders and onto the back, which can be raised (piloerec-tion) to increase apparent body size. This effect can be emphasized because these erectile hairs are often of a contrasting color to the rest of the body, thus drawing attention to the display. Striking body coloration patterns, often involving contrasting colors or shades, are commonly used in displays by members of the Bovidae.

Activity patterns and migratory movements

Rumination imposes regular, alternating periods of feeding bouts, followed by rest-rumination periods. Depending on habitat type and to a lesser extent group size, after feeding, the animal will move to more predator-secure habitats to rest and ruminate. The diurnal pattern of these activities can also be affected by predation pressure, especially hunting by humans, with the result that animals become crepuscular, feeding primarily around dawn and dusk. Nocturnal feeding also occurs, but seems to be most frequent during moonlit nights.

Bovids usually make seasonal use of their environment by occupying different habitats at different times of the year. Most seasonal movements or migrations are related primarily to food availability. In temperate regions, bovids move to different areas, often according to the seasons, attempting to find the best foraging conditions available to them. Thus in winter, they congregate in areas where there is not only adequate food, but also shallow snow, shelter from harsh climatic conditions, and habitat or terrain to avoid predators. In spring, the animals move to sites where snow melts early and forage begins to grow. In summer, further movements occur to sites where there is abundant and nutritious forage that will allow the animals to acquire sufficient energy to meet not only their immediate needs, but also enough to deposit fat for winter. Males need high-quality habitat so they can store fat that supports them during the rut. In mountainous areas, the migrations are usually altitudinal and related to snow accumulation and plant growth. Animals in these areas often spend the winter at low elevations where snow depths are usually shallow and forage more available. In spring, the animals migrate upward, following the greening of new vegetation as the snowline retreats. Snow accumulation in fall and early winter then forces them to lower elevations, unless they can forage along snow-free windswept ridges. In the tropics, migrations occur as animals take advantage of new forage growth during rainy seasons. In exceptional cases, populations may make extremely longdistance migrations each year. For example, blue wildebeest in Serengeti have an annual migration of almost 2,000 mi (1,200 km) round trip. These migrations in tropical regions achieve the same ecological benefits as those in temperate regions. Animals move about their environment to exploit seasonal foraging opportunities and thus increase their reproductive success or reduce their mortality.

Overcome Shyness 101

Overcome Shyness 101

You can find out step by step what you need to do to overcome the feeling of being shy. There are a vast number of ways that you can stop feeling shy all of the time and start enjoying your life. You can take these options one step at a time so that you gradually stop feeling shy and start feeling more confident in yourself, enjoying every aspect of your life. You can learn how to not be shy and start to become much more confident and outgoing with this book.

Get My Free Ebook

Post a comment