Phacochoerus africanus and Phacochoerus aethiopicus
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Photo courtesy of http://www.cruisersafaris.com/hunting_package_2.htm
This page was created by Jessikah Byington, jebyington@davidson.edu, as a student web site for Biology 323, Animal Behavior, at Davidson College http://www.bio.davidson.edu/people/vecase/Behavior/index.html.
Photo courtesy of http://home.vicnet.net.au/~neils/africa/warthog.htm
The warthog is known as the naked swine of the savanna (Spook). They get their name from the large warts found on their head (Kleiman et al., 2004; Spook). The warthog is a member of the Suidae family (Kleiman et al., 2004). The Phacochoerinae, or warthog, is one of the three subfamilies of the Suidae (Kleiman et al., 2004). The two extant species of warthog include the Phacochoerus africanus, the common warthog, and the Phacochoerus aethiopicus, the desert warthog (Kleiman et al., 2004).
Warthogs are typically 39-59 inches in length and 21.5-38 inches in height (Kleiman et al., 2004). Males are slightly larger than females; males weigh between 150-220 pounds and the female weighs between 99-156 pounds (Spook). They are found in variety of colors from light red to brown and gray to mostly black (Kleiman et al., 2004). Newborns are dark brown in color with light spots (Kleiman et al., 2004). They have a large flat face with prominent tusks (Kleiman et al., 2004). The upper tusks average about 8-24 inches in length and the lower tusks are about 4 inches in length; both tusks are much shorter for the female (Spook). Another key physical aspect of male warthogs is the presence of warts on their face (Kleiman et al., 2004). On the male, large warts are located below the eyes of the male and can be up to 6 inches long (Spook). The warts are mere bumps on the females and young (Spook).
Warthogs can tolerate higher than normal body temperatures, which is believed to be due to their ability to conserve moisture inside their body (Warthogs). They have also been known to cope with low temperatures (Vercammen). Behavioral strategies, such as wallowing and huddling together, are used to help them tolerate high and low temperatures respectively (Vercammen). Their lack of hair and sub-dermal fat leaves them very poorly insulated, in turn, huddling together and other such warming behavioral strategies are essential (Vercammen).
Warthogs live for approximately 18 years (Warthogs). A study conducted by Spinage (1972), showed that warthogs departed from the typical survival curve of African ungulates. Warthogs have a heavy age-constant number of deaths for most of their life. The warthog differed from the other species in Spinage's study not in its potential length of life, but in its high reproductive rate. The other species are monovular, but the warthogs are polyvular, with annual litters of 2-7 offspring. Such a high reproductive rate is offset by a high mortality rate. Warthogs have almost an equal chance of dying at any age up to middle-age; in contrast, the chances of survival of the other ungulates tend to increase over this period. Therefore, it is the reproductive rate which thus apparently determines the pattern of survival, not bodily size or length of lifespan (Spinage 1972).
Warthogs prefer moist habitats with plentiful vegetation and tend to avoid drier, open areas (Kleiman et al., 2004; Spook). They are found in the Northern and Southern Savanna, but are absent from deserts, rainforests and mountains above 10,000 feet (Kleiman et al., 2004; Spook). Specifically, warthogs are found from Somalia to east and southern Zaire down to Cape Province in South Africa (Kleiman et al., 2004). Their presence has also been noted on Madagascar and on Mayotte Island (Kleiman et al., 2004).
Distribution of Warthogs from http://www.wildlifesafari.info/warthog.html
Warthogs are mainly diurnal animals and sleep in self-excavated burrows or in heavy thickets of vegetation during the day (Kleiman et al., 2004). Most of the holes that warthogs use for sleeping and protection have been excavated by aardvarks (Kleiman et al., 2004; Spook).
Warthogs are omnivores, consuming roots, bulbs, fungi, fruit, eggs, invertebrates, birds, small mammals, and carrion (Kleiman et al., 2004). Warthogs have a very keen sense of smell, which they use to find food (Warthogs). They won't hunt other animals for food (Warthogs). Their snouts are used to root in the ground and can often do serious damage to crops in a short amount of time (Kleiman et al., 2004). Due to their ability to exploit buried and highly nutritious rhizomes and bulbs, as many as 78 warthogs per square mile are able to thrive in the best habitat (Spook). They drink regularly and in hot, dry weather they use wallows daily (Spook). However, they are the only pigs able to live in areas without water for several months of the year (Spook).
Social Spacing and Social Organization
Photo courtesy of http://home.vicnet.net.au/~neils/africa/warthog.htm
Warthogs live in home ranges that range from 158-924 acres, the average being 430 acres (Spook). Warthogs' social spacing is not considered a territory because individuals and groups do not defend or exclusively use a space (Maher 1995). Territorial behavior is predicted when benefits outweigh the costs or when it will be economically defensible (Maher 1995). Warthogs’ resources are not economically defensible; resources are sufficiently plentiful and exist in very large clumps, so they are able to acquire enough without having to defend a space (Spook). It is a waste of energy trying to defend something one does not have to (Case 2004). Also, territorial defense increases conspicuousness to predators which would leave the already small and slow warthog very vulnerable to their predators (Case 2004).
Males tend to live alone or in small bachelor groups with changing membership (Kleiman et al., 2004). Mature males only join female groups when sows are in heat (Spook). Males are not territorial, but will fight among themselves for mating opportunities, sometimes causing serious wounds with their upper or lower tusks (Warthogs). Females live in sounders that share the same resources (Kleiman et al., 2004). A sounder is made up of one to three females and their offspring (Kleiman et al., 2004). If sounders have four to five sows, the group can number up to 16 warthogs (Spook). Females often remain in the natal group for several breeding seasons; males leave the group, yet remain on the natal home range (Kleiman et al., 2004). Single males, bachelor groups, and several sounders often use the same home range simultaneously (Kleiman et al., 2004). Collectively, a group sharing a home range is known as a clan; family groups are territorial (Kleiman et al., 2004). Females and their young travel about 4.3 miles in daylight and then retire before dark into secure sleeping burrows within their home range (Spook). Burrows are used by different sounders on a first-come, first-serve basis (Spook). Warthogs often mark their sounder territories by spraying urine and wiping saliva from their mouths against objects (Warthogs).
Photo courtesy of http://home.vicnet.net.au/~neils/africa/warthog.htm
Two facial glands of the warthog, the sebaceous gland, which is the tusk gland located in the upper lid behind the tusks, and the preorbital gland are found to be important to warthogs' daily lives.
The study by Estes et al. (1982), observed the varying marking behaviors of warthogs using the tusk glands. Both males and females were found to start marking at six to seven months, but males marked more often than females. The things commonly marked included sleeping and feeding sites, waterholes, and trees bordering paths. The tusk gland secretion is found to be involved in warthog courtship and agonistic interaction. Another function of the tusk gland includes communicating status and establishing identity of individuals sharing the same range. This is particularly key to warthogs since males are solitary and live with one or more females in which their home ranges overlap. Also, the height of scent and tusk marks could provide clues to the largest most dominant males in the area. These signs are particularly useful in species with a mating system based on absolute dominance; they all try to make their marks as high as possible, essentially advertising size. The markings may then lead to repelling rivals or attracting receptive females.
Vocalizations by warthogs often occur during simple maintenance activities and reflect low levels of the animal's general motivational state. Such simple vocalizations automatically emphasize the animal's presence and advertise its position. Animals that are establishing their presence and position at a considerable distance use relatively loud vocalizations. However, the warthog is found in considerably open environment, so their vocalizations establishing presence need not be as loud. Many ungulate vocalizations are intimately related to increasing level of excitement and usually are emulative. Not only do the vocalizations reflect different levels of the animal's general mood but are also indicative of specific internal states and are restricted to specific situations (Walther 1984).
Excitement activities, movements and vocalizations indicating that an animal is in an unspecific state of agitation, are often nothing but maintenance activities. They are exactly like daily activities shown everyday, yet in certain exciting situations they occur more frequently than under normal conditions. Common behavioral examples for hoofed animals are self-grooming, shaking, tail wagging, walking up and down, stamping as if bothered by flies, etc. A typical movement of some species, particularly the warthog, is the vertical erection of the tail. Other excitement activities are symptoms of an arousal within the autonomic nervous system (Walther 1984).
There are special mother-offspring vocalizations. There are often "question-answer" vocalizations between mother and offspring. Sounds made by the young are higher in pitch than those made by adult animals, but they are nothing more than the infantile forms of adult vocal contact sounds. The mother reacts to the calls of her young by calling back or approaching the young who is calling. If a female warthog is lying with her young in a nest and one of the young makes a distress call, the mother immediately changes their position. Nursing is a very important interactions between mother and offspring and often requires some communication. With "follower" species, like the warthog, the nursing of young is initiated by the mother through vocalizations (Walther 1984).
Specific movements and vocalizations accompany threat displays. It is characteristic of the warthog to growl loudly when fighting. Also it is common for the warthog and other ungulates, as well as animals without horns or tusks, to take part in head-nodding or head-throwing. In most species the upward head movement is quite vehement, but in the warthog it is slow and deliberate. The upward blows of their head are used during fighting. However, some movements that may appear to be threat displays are actually dominance displays. Certain postures or movements may be considered threats displays in some species and dominance displays in others. One of the most important types of dominance displays involves the broadside position or lateral T-position. While some species use the lateral T-position to initiate a fight, the warthog uses the broadside position merely as a dominance display. The warthog commonly fights from a frontal position. Displaying warthogs circle the opponent, with ruffled mane and stiff legged gait, until they come into a frontal position from which fighting may develop (Walther 1984).
Photo courtesy of http://www.seaworld.org/AnimalBytes/warthogab.html
Warthogs are promiscuous (Kleiman et al., 2004). For promiscuity to occur the male's investment in offspring is limited to sperm and the female raises young mostly alone (Ehrlich 1988). It is presumed that promiscuous mating systems can evolve only where the advantage of the male remaining with the female to help in raising the young is negligible (Ehrlich 1988). Specifically, warthogs utilize a form of promiscuity known as overlap promiscuity (Sandell 1992). This is the mating system of choice for over 60% of mammals (Case 2004). It is typical of animals with large home ranges in which the males have ranges overlapping several females and the daily behavior of the female is unpredictable (Case 2004). This type of mating system is advantageous to the male for he doesn't defend a resource or the female, he merely roams, following his ultimate strategy. (Case 2004). The females are slightly disadvantaged for they don't get any resources from the male (Case 2004).
Overlap promiscuity was further investigated in a study by Sandell (1992). This study analyzed systems with solitary, stationary, and randomly distributed females, no paternal care, and no female choice. A male has two options to achieve matings: (1) he may employ a "staying tactic" and stay to defend one or a number of females or a critical resource that will give him access to females using that resource, or (2) he may adopt a "roaming tactic," wandering around in search of receptive females and competing for each mating opportunity. The first tactic will result in a system of female-defense or resource-defense polygyny. The second tactic, to roam, will give rise to overlap promiscuity. Animal mating systems and spacing patterns are strongly influenced by environmental conditions, giving rise to large variations in behavior, even among populations of the same species. The type of mating system and spacing pattern are the results of the behaviors performed by the individuals in the population. However, in most cases, the success of a given tactic depends on the tactics employed by the other individuals in the populations. There are many factors that influence male mating tactics and the result of any one factor can be influenced by other factors.
Reproduction is a process of maximization; that is, if it is possible to achieve a higher lifetime reproductive success by another tactic, then this will be the realized tactic. Most classifications of animal mating systems make a clear distinction between monogamy and polygyny. However, there are cases when this distinction conceals the causal connections. For example, males may end up guarding a single female (i.e. being monogamous), whereas the same tactic of staying employed under a somewhat different female distribution will result in polygyny. From a functional aspect the males are employing the same mating tactic, but the environmental conditions lead to different outcomes (Sandell 1992).
Warthogs utilize overlap promiscuity as their mating system of choice for it best fits their social structure and habitat (Sandell 1992). Male warthogs adopt the "roaming tactic" in order to achieve matings since the females are generally spread out in sounders (Case 2004). The wide dispersal of female groups is possible given that their food is not rich in just one area; food is an essentially indefensible resource making it unprofitable for males to defend (Case 2004).
In the warthogs' mating season, group members greet after a separation with explosive grunts and nose-to-nose contact (Warthog). Males attacking other males is also characteristic around mating time (Warthogs). The only time males will fight among themselves is for mating opportunities (Kleiman et al., 2004). Warthogs are seasonal breeders (Kleiman et al., 2004; Spook). They mate as rains end and farrowing 160 to 170 days later as rainy season begins (Kleiman et al., 2004; Spook). Both sexes are fertile by 18 or 19 months, but very few males breed before turning four (Kleiman et al., 2004;Spook).
Photo courtesy of http://www.chipembele.org/orphans.htm
Sows isolate to farrow and stay underground nurturing hairless piglets for the first week after young are born (Spook). The size of the litter ranges from one to six, but three to four piglets is most common (Kleiman et al., 2004). The piglets remain in the burrows for six to seven weeks except for brief excursions or to change dens (Spook). Once the six or seven weeks has passed, the piglets accompany their mother everywhere, filing behind the sow in fixed order (Spook). The young are weaned by six months (Spook). Warthogs are known as a "follower" species; the young are kept nearby at all times (Walther 1984).
Mammals have been found to show extensive interspecific variation in the form of maternal care. In a study by Fisher et al. (2002) a dichotomy was found between ungulate species in which offspring follow the mother versus ungulate species in which offspring remain concealed. The differences between species in the form of parental care are due to a similar interaction between habitat, social behavior, and life history. Adaptive explanations for the dichotomy in maternal care strategies in ungulates have usually been based on the method used to protect offspring from predators, assuming a causal link between the ecology of predation and evolution of behavior. In the study by Fisher et al. (2002)it was hypothesized that the deficiency of concealing cover is positively related to the evolution of following behavior. The results of the study supported this hypothesis. Habitat structure was very strongly related to maternal care strategies in ungulates. The study also showed that large-bodied ungulate species were more likely to be followers. The proportion of time spent hiding was negatively related to body mass in ungulates. Additionally, the hypothesis that gregarious species are more likely to have evolved following behavior received some support in ungulates. There was also some support for a newly studied hypothesis that the following style of maternal care is associated with the evolution of delayed weaning and therefore a slower life-history strategy in ungulates. Hiding is shown to be an ancient trait in ungulates. Varying groups of animals have evolved following and hiding behavior as a solution to the same challenge, but on different continents. Hiding and following strategies have evolved as alternative tactics of predatory avoidance.
Photo courtesy of http://www.sandiegozoo.org/phototrek/2001/warthogs.html
Associated mother warthogs suckle one another's young (Spook). Cotgreave (1998) explored the question of why a female would forego her opportunity to pass on her own genes into next generation and, instead, help to raise somebody else's young. The answer to this question is kin-selection. The youngsters that a female helps to raise will share some of her genes, so it pays to invest in them. Kin-selection depends on two factors; one, how closely the female is related to the young and two, the risk the female runs in moving away and attempting to breed herself (Cotgreave 1998).
Jensen et al. (1999) conducted a study on allosucking in warthogs. Allosucking, non-offspring nursing, is most common among species that form small social groups and have larger litters, like the warthog. Warthogs are cooperative breeders in that females will nurse foster offspring if they lose their own litter. Of the 16 breeding groups of warthogs studied by Jensen et al. (1999), 11 contained two or more nursing females. Allosucking occurred in six of these groups (55%). Explaining the evolution of allosucking is challenging. It is costly to the providing female since it can increase mortality etc., so the benefits are assumed to be high in order to counterbalance the negative effects. However, many studies have failed to show the benefits of allosucking. Potential benefits of allosucking include: increase juvenile growth because more milk will be available; mothers' of allosucked offspring stop lactating sooner which leads to shorter inter-birth intervals and larger subsequent litters; females donating milk to non-offspring could benefit through access to mates, breeding territories and other resources through gaining experience in the care of young; milk may become like currency of exchange - donors gain access to groups. Warthogs are facultative, meaning they display a wide range of breeding strategies and their social organization is based on matriarchal groups. In this study, varying aspects of warthog allosucking were examined. From this study, it was concluded that allosucking was not a case of mistaken identity or milk theft, females can distinguish between juveniles, they can nurse selectively, and that four to five-year-olds are less likely to be donors. Reciprocity has served as an explanation for allosucking in some species; however, the observed asymmetry in nursing behavior within groups of allosucking warthogs makes reciprocity an unlikely explanation in this study.
It is possible that allosucking in warthogs is a sign of kin altruism (Spook). The allosucking takes place in the sounders where the females are almost always related (Kleiman et al., 2004). Warthogs make a sacrifice in order to suckle their relative's young; for example, they could be spending more time finding food or taking care of their own young (Case 2004). Although it will also increase their own inclusive fitness, it is not ultimately selfish since there are costs to allosucking another's young (Case 2004). Jensen et al. (1999) found in his study that allosucking was never a case of mistaken identity or milk theft. This seems to suggest that the warthog intentionally performs allosucking at a cost to themselves; therefore it is a sign of kin altruism (Case 2004).
Photo courtesy of http://www.keithv.com/africa5.html
When it comes to fighting, warthogs would rather run than fight, but they can be very fierce if forced to fight (Warthogs). They are known for ferociously defending their family (Warthogs). Warthogs can reach a top speed of 34 mph in emergencies (Spook). It is characteristic of warthog to run with its tail straight up like an antenna (Spook). Warthogs are slower and have less endurance than most savanna ungulates; therefore, burrows are essential to their safety when being chased (Spook). Also, warthogs have poor eyesight, putting them at an even greater disadvantage (Warthogs). Some of their typical predators include cheetahs, wild dogs, and the spotted hyena (Spook). Burrows do provide much needed protection for warthogs, particularly at night, yet leaving the burrows in the morning can be risky for lions often sniff out occupied burrows at night (Spook). Juveniles often have very low survival rates (Vercammen). Their vulnerability to prey along with their susceptibility to cold exposure and malnutrition during drought result in juvenile survival rates of less than fifty-percent during the first year (Vercammen).
The spacing between differing species of African ungulates was found to be minimal in a study by Sinclair (1985). Interspecific competition has been the suggested process for producing resource partitioning and coexistence of African ungulates, yet evidence brought forth in this study by Sinclair (1985) has pointed to predation and other alternative hypotheses. Warthogs and other ungulates in Africa are influenced by both predation and interspecific competition; therefore, they may be showing a mixed evolutionarily stable strategy in order to cope with the two opposing pressures. Undoubtedly, predation was found to play as important a role as interspecific competition in structuring the African ungulate community. All the species in this study, except for the wildebeest, were observed closer together than expected. This suggests that predation has resulted in ungulate species remaining together for mutual protection in multi-species herds. This phenomenon shows clear evolutionary significance.
Leuthold et al.(1975) also observed the social grouping of ungulates in parts of Africa. He found that in open-country, ungulates tend to form larger herds; he also characterized this behavior as an anti-predator response.
Photo courtesy of http://www.mcdcwain.freeserve.co.uk/warthog.htm
Warthogs are diurnal ungulates found in various parts of Africa. The two extant species of warthog include the Phacochoerus africanus, the common warthog, and the Phacochoerus aethiopicus, the desert warthog. Warthogs prefer moist habitats with plentiful vegetation and tend to avoid drier, open areas. They are found in the Northern and Southern Savanna, but are absent from deserts, rainforests and mountains above 10,000 feet. Warthogs sleep in self-excavated burrows or in heavy thickets of vegetation during the day. Most of the holes that warthogs use for sleeping and protection have been excavated by aardvarks. Warthogs are omnivores, consuming roots, bulbs, fungi, fruit, eggs, invertebrates, birds, small mammals, and carrion.
Warthogs have a home range since their food is not economically defensible. Males tend to live alone or in small bachelor groups with changing membership. Mature males only join female groups when sows are in heat. Males are not territorial, but will fight among themselves for mating opportunities, sometimes causing serious wounds with their upper or lower tusks. Females live in sounders that share the same resources. A sounder is made up of one to three females and their offspring. Collectively, a group sharing a home range is known as a clan.
Two facial glands of the warthog, the sebaceous gland, which is the tusk gland located in the upper lid behind the tusks, and the preorbital gland are found to be important to warthogs' daily lives. The tusk gland secretion is found to be involved in warthog courtship and agonistic interaction. Another function of the tusk gland includes communicating status and establishing identity of individuals sharing the same range. This is particularly key to warthogs since males are solitary and live with one or more females in which their home ranges overlap. Also, the height of scent and tusk marks could provide clues to the largest most dominant males in area.
Warthogs utilize overlap promiscuity as their mating system of choice for it best fits their social structure and habitat. Male warthogs adopt the "roaming tactic" in order to achieve matings since the females are generally spread out in sounders. This mating system is typical of animals with large home ranges in which the males have ranges overlapping several females and the daily behavior of the female is unpredictable. This type of mating system is advantageous to the male for he doesn't defend a resource or the female, he merely roams, following his ultimate strategy. The females are slightly disadvantaged for they don't get any resources from the male.
The differences between species in the form of parental care are due to a similar interaction between habitat, social behavior, and life history. Hiding and following strategies have evolved as alternative tactics of predatory avoidance. Warthogs have a following strategy in which the young are kept nearby at all times.
Associated mother warthogs suckle one another's young, a reliable sign of kinship. Allosucking, non-offspring nursing, is most common among species that form small social groups and have larger litters, like the warthog. Warthogs are cooperative breeders in that females will nurse foster offspring if they lose their own litter.
When it comes to fighting, warthogs would rather run than fight, but they can be very fierce if forced to fight. They are known for ferociously defending their family. Warthogs are slower and have less endurance than most savanna ungulates; therefore, burrows are essential to their safety when being chased. Some of their typical predators include cheetahs, wild dogs, and the spotted hyena.
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