Brown Hyena
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And Comparisons with the Spotted Hyena (Crocuta crocuta)
Brown Hyena
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Habitat and Habitat Utilization
Habitat and Habitat Utilization
The brown hyena is a relatively rare animal that resides in scattered groups throughout Southern Africa. The majority of the African region occupied by the brown hyena has been largely uncharacterized, so there is little known about the actual numbers and dispersion of the species. Some areas occupied by the brown hyena include the central and southern portions of the Kalahari desert, the Kruger National Park, the Umfolozi Game Reserve, the Moremi Game Reserve, the Namib Desert Park, and the Etosha National Park (Skinner 1976). Some of these areas are extremely hot and dry, such as the Kalahari and Namib Deserts. Other areas within the brown hyena range in Southern Africa have more forgiving climates consisting of dry open scrub and woodland savannah. A map of the distribution of the brown hyena in Southern Africa appears below.
The brown hyena is a solitary forager, feeding opportunistically on a variety of scavenged animal remains (Mills 1983a, Mills 1983b, Skinner et al. 1995). For example, in the Kalahari, there is a clear preference for remains of giraffe, gemsbok, and wildebeest killed by other predators (Owens & Owens 1996). Along the Namib Desert coast brown hyenas feed mostly on seal carcasses washed up on shore (Skinner et al. 1995). However, it is important to note that the availability of food typically varies seasonally. For example, the food supply in the Kalahari is usually adequate enough to support the hyena groups during the rainy season when herds of ungulate prey are prolific (Owens & Owens 1979a, Owens & Owens 1996). However, during the dry season, the hyenas are often forced to rely on other sources of food, such as vegetable matter, ostrich eggs, bones, insects, reptiles, and small mammals such as birds and rodents (Owens & Owens 1996, Skinner 1976). The brown hyena is incapable of hunting and taking down large prey, though it successfully hunts small mammals when necessary (Skinner 1976). The majority of scavenging is accomplished alone at night (Owens & Owens 1979b, Skinner 1976).
Brown hyena groups typically occupy a den. These dens are
usually leftovers from aardvarks, porcupines, or warthogs (Skinner 1976).
The den has between one and three entrances, which are only large enough
for cubs to enter, preventing access by predators (Mills 1983a, Owens &
Owens 1979b, Skinner 1976). Therefore, the main purpose of the den
is in protection of young (Skinner et al. 1995). A brown hyena group
typically uses several dens: a central communal den and several smaller
satellite dens (Skinner et al. 1995). A brown hyena mother typically
gives birth and raises her cubs in a satellite den for the first three
or four months of their life. The cubs spend the first few months
of their life inside the den and emerge only to suckle from their mother,
who announces her arrival by making a soft purring sound. At about
four months of age the mother may move the cubs to the communal den (Skinner
et al. 1995). As the cubs age they begin to emerge from the den for
longer and longer periods, until they eventually embark on foraging trips
at the age of one year. After about 15 months of age the cubs no
longer use the den (Mills 1983a). As the cubs mature into subadults
they either remain in the clan or are forced out by older members of the
same sex (Owens & Owens 1979b). The social life of the group
is centered at the den. Other group members sleep in depressions
surrounding the den (Owens & Owens 1979b).
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General Description of the Brown Hyena and Its Social System
The brown hyena resembles the spotted hyena in shape and physical appearance. Skinner (1976) describes the brown hyena as having a hyena-like appearance, with steeply sloping hindquarters, a broad head, short jaw and muzzle, pointed ears, and short tail. Probably the most distinguishing characteristic of the brown hyenaâs physical appearance, at least compared to other hyena species, is its thick coat (Skinner 1976). It is not known why this feature evolved, but it has been noted that it is a useful adaptation among brown hyenas living on the Namib desert coast, where conditions are very cold, especially during the winter (Skinner et al. 1984).
The brown hyena is also smaller and more slender than the spotted hyena. The male brown hyenas average about 44 kilograms in weight, while spotted hyena males average about 56 kilograms. Female brown hyenas average about 41 kilograms, while female spotted hyenas average 61 kilograms (Skinner 1976). Males have slightly greater body length than do females, measuring about 1.2 meters and 1.13 meters, respectively. In contrast, the female spotted hyena is longer than her male counterpart, measuring in at 1.33 meters, while the male average is 1.29 meters (Skinner 1976).
Brown hyenas live in clans of between four and fourteen individuals (Skinner et al. 1995, Owens & Owens 1979a and 1979b, Mills 1982). A typical Kalahari clan consists of one dominant adult male, between one and four subordinate adult males, four to six adult females, two other subadults, and cubs (Owens & Owens 1979a and 1979b). These clans occupy a large home range with several dens. The size of these home ranges varies from 32 square kilometers in the Namib desert (Skinner et al. 1995) to 480 square kilometers in the Kalahari (Mills 1983b). However, not all brown hyenas live in clans. Brown hyenas can be divided into three classes of individuals: clan members, dispersing subadults, and nomadic males and females (Mills 1983b). In contrast, the spotted hyena lives in clans of between 30 and 80 individuals (Gorman & Mills 1984). The females in a spotted hyena clan are all from closely related matrilines, and there is a high turnover in the male component of the clan (Frank 1986b).
One of the more interesting features of the brown hyena is the
lack of sexual dimorphism. The male and female are almost identical
in size (Skinner 1976, Owens & Owens 1996), and their genitalia are
very similar in appearance. Monomorphism in the brown hyena is not
as severe as in the spotted hyena. Male spotted hyenas are smaller
than females and are subordinate to them, and spotted hyena females have
notably masculinized genitalia. Owens and Owens (1996) feel that
the monomorphism of brown and spotted hyenas evolved separately.
The monomorphism of the spotted hyena has likely resulted from intense
scramble competition between females for food, which does not occur in
the brown hyena.
Spotted hyenas in the Maasai Mara, Kenya. Photographs
were taken by me.
Social Spacing
As mentioned earlier, brown hyena clans occupy a large home range. In the Namib desert a home range was observed to be as small as 32 square kilometers (Skinner et al. 1995). In the central Kalahari a home range was observed to be 170 square kilometers in size (Owens & Owens 1979a). In the southern Kalahari home ranges have been observed to vary in size from 235 to 480 square kilometers (Mills 1983b).
Though much of the literature describes the space occupied by a brown hyena clan as a territory, it is more appropriate to classify the space as a home range in most cases. This is the case for several reasons. First, these territories are very large and there is almost always overlap between neighboring home ranges. For example, Mills (1983b) notes that there is as much as a 20% overlap in home ranges between neighboring southern Kalahari brown hyena clans. In addition, Mills and Mills (1982) note that the area of overlap between two neighboring brown hyena groups in the southern Kalahari lies in a riverbed, the most heavily traveled portion of both home ranges. In contrast, Namib desert brown hyena groups have been observed to occupy smaller territories with little overlap (Skinner et al. 1995). It would be expected that a classical territory would have to be fairly small in order for the hyenas to be able to defend the borders. This is true of the Namib desert hyena territories. Even in the southern Kalahari, where the territories range in size from 235-480 square kilometers, Gorman and Mills (1984) observed aggression between hyenas at territorial boundaries, though individuals from neighboring groups met only rarely. Still, the large area occupied as well as the overlap is more suggestive of the presence of a home range.
Another distinguishing feature of the brown hyena is scent marking behavior. Scent marking is an important behavior of the brown hyena that serves to maintain the social spacing of neighboring clans. Brown hyenas have an anal gland from which they secrete a paste-like substance that is used for scent marking (Gorman & Mills 1984, Mills 1983b, Owens & Owens 1979b). This paste is composed of a white secretion of lipids as well as a black watery liquid. Brown hyenas deposit this secretion on grass stalks throughout their range. This is called pasting (Gorman & Mills 1984). In addition, brown hyenas regularly defecate in common areas called latrines (Gorman & Mills 1984). Mills (1983b) feels that scent marking serves two purposes. First, it is an important method of intragroup communication. Because the brown hyenas are solitary and seldom encounter other group members, pasting is an important method of communicating to other group members that an area has been recently foraged, in order to prevent other members from wasting their time. Second, scent marking is an important method of intergroup communication that mainly designates the boundaries of the range. Gorman and Mills (1984) have observed that brown hyenas distribute scent marks fairly evenly throughout their range, with a slightly higher concentration in the center. The same authors contrast this behavior with that of spotted hyenas, which paste almost exclusively along territorial borders. In addition, the spotted hyena clans typically will viciously defend their territories against other intruding hyenas (Kruuk 1972). Moreover, spotted hyenas often gather in groups to participate in boundary defense (Kruuk 1972). Brown hyenas are also known to show aggressive behavior toward intruding hyenas at the territorial boundary, mainly in the form of aggressive neck-biting (Mills 1983b, Owens & Owens 1996). However, this happens far less frequently than it does in the spotted hyena because the range is significantly larger and individuals meet less frequently (Mills 1983b). Therefore, the space occupied by brown hyena clans is more appropriately described as a home range because it is both too large to be defended and it is defended with much less vigor than spotted hyena territories.
The supply and dispersal of food is the greatest factor affecting territory
and group size in the brown hyena. The greatest evidence of this
is seen in the increase of range size during the dry months when food is
less plentiful. Owens and Owens (1996) noted that the distance traveled
during foraging trips and subsequently the size of the home range increases
during the dry months when the food supply in the central Kalahari is scarce.
When the rains return and herds of migratory prey re-enter the habitat
the brown hyenas do not have to travel as far to find food. Mills
(1982) suggests that the distribution of food throughout the home range
affects the size of the range, while the quality of food affects the size
of the group. In the central Kalahari, where food is both disperse
and of generally poor quality, even during the rainy season (Owens &
Owens 1984), the size of the brown hyena clan is therefore small and neighboring
clans are more spread out. This explains the large home range of
the brown hyena. The food supply is the greatest influence on the
social organization of the brown hyena (Mills 1982). In the Namib
desert, the supply of seal carcasses is plentiful most of the year.
Still, one brown hyena clan living there was found to occupy a large 220
square kilometer home range, while another clan occupied a 32 square kilometer
territory (Skinner et al. 1995). The 32 square kilometer territory
provided adequate food for the clan, yet the other clan occupied a much
larger range despite the abundance of food. The authors suggested
that the 220 square kilometer range represented cultural inheritance of
space, rather than need for food. The harsh climate of the Kalahari,
on the other hand, necessitates the use of a large home range even to support
a small hyena clan.
The distribution of food affects several other aspects of the brown
hyena social system. The evolution of communal denning is likely
a response to the need for brown hyenas to spend the majority of their
time away from the den on foraging trips (Owens & Owens 1979b).
In addition, food supply affects the type of mating system. In the
dry months when food is more scarce, the mating system of central Kalahari
brown hyenas has been observed to switch from polygyny to promiscuity.
This probably occurred because the dominant clan male no longer was able
to defend the alpha female as she took more extensive foraging trips throughout
the range (Owens & Owens 1996). Thus, food supply in the brown
hyenaâs habitat affects several aspects of its social system.
Brown Hyena
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Social Relationships and Mating
Female brown hyenas are polyestrus and individual estrus
periods usually last one week, during which time the female will mate.
As with the spotted hyena, mating consists of numerous short-duration mountings
that are spread out over several days (Mills 1983a). The male and
female are typically apart much of this time as well. Unlike the
spotted hyena, the dominant brown hyena female is equal in status to the
dominant male brown hyena. Therefore, both the male and female
will approach each other in an attempt to mate (Mills 1983a), while in
the spotted hyena the female controls the mating encounters (Kruuk 1972).
As mentioned earlier, the cubs are initially raised in satellite dens and
are then transported to the communal den. The litter typically ranges
in size from two to four cubs, with an average of three (Skinner 1976).
The mating system of brown hyenas has been extensively characterized
in the southern and central Kalahari. The primary mating system that
has been observed is promiscuity. In the southern Kalahari, group-living
females have been observed to mate only with nomadic males (Mills 1982,
Mills 1983a). The group-living males were not observed to interact
sexually with group-living females, and did not defend them (Mills 1982).
A slightly different mating system was observed among brown hyenas of the
central Kalahari. Uni-male polygyny has been observed among central
Kalahari brown hyenas (Owens & Owens 1996). In this mating system,
an immigrant adult male brown hyena takes up residence in a clan, defends
the range, and mates with the females in the clan (Owens & Owens 1984b).
However, the tenure of this male is not permanent, and lasts no longer
than 26 or 27 months (Owens & Owens 1984b). It is important to
note that the authors recorded sexual interaction between the group females
and nomadic male hyenas during the tenure of the dominant immigrant adult
male, and though this did not occur frequently, it suggests a promiscuous
mating system (Owens & Owens 1984b). Moreover, the authors observed
occasional sexual interaction between nomadic female hyenas and dominant
group living adult males. Though the primary mating system in this
population is polygyny, promiscuous sexual encounters occasionally occur.
As mentioned earlier, the dispersion and quality of food affects the type
of mating system. During the dry season when food is scarce, it is
more difficult for the dominant group living males to defend the females
in the group as they take more extensive foraging trips in search of food
(Owens & Owens 1996). Therefore, promiscuity develops during
times of food shortage.
This is not dissimilar to the mating system of the spotted hyena. The prevailing mating system of spotted hyenas in the Masai Mara game reserve is polygyny, though promiscuity appears to arise from time to time as well. There is one dominant group-living male who receives all the copulations from females (Frank 1986b). This situation usually prevails, but occasionally a subordinate male will sneak a copulation while the dominant individual is mating (Frank 1986b). Thus, promiscuity occasionally arises.
The occurrence of nomadic adult male brown hyenas is constant throughout all brown hyena populations. Therefore, this must be an evolutionarily stable strategy. Mills (1982) suggests that nomadism is a good mating strategy because brown hyena territories are too large and group members are too scattered for a dominant clan male to prevent other males from mating with clan females. Moreover, there are several notable disadvantages associated with alpha male status in a brown hyena clan that make nomadism even more favorable, namely territorial defense (Owens & Owens 1996). Nomadic males avoided all these costs, and actually mated with clan females just as frequently as alpha males, according to Owens & Owens (1996). The only significant benefit for clan life for the alpha male was increased feeding time. It is important to note, however, that while clan living may be disadvantageous for males, it is highly advantageous for reproductive females who are rearing offspring (Owens & Owens 1996). This will be discussed below.
There are relatively few interactions between adults of the same sex in brown hyena clans. Owens and Owens (1996) note that adults are seldom together because brown hyenas are not involved in any group activities that require participation of many individuals, such as hunting. Any interactions that do occur between adults serve to establish the dominance hierarchy characteristic of brown hyena clans. For example, central Kalahari brown hyenas are characterized by separate linear dominance hierarchies within each sex, in which the highest-ranked male is equal in status to the highest-ranked female (Owens & Owens 1996). Both individuals are dominant over all other individuals in the clan except each other. These dominance hierarchies are maintained by aggressive neck-biting encounters between members of the same sex but not between members of opposite sexes (Mills 1983b, Owens & Owens 1996). The neck biting is more aggressive and frequent between females, and in one clan observed the same alpha female was dominant for almost six years until her death (Owens & Owens 1996). The advantage to dominance is mainly in greater access to food and higher reproductive success (Mills 1983b, Owens & Owens 1996). It is important to note that no aggression was recorded between brown hyena clan members in the southern Kalahari. Mills (1983b) reached an important conclusion from this observation. His explanation for these findings is that the density of hyenas and neighboring clans is higher in the central Kalahari than in the southern Kalahari. Therefore, the brown hyenas of the central Kalahari must be more aggressive to retain access to food. Due to the high competition for food, the habitat could not support more individuals and larger groups, and aggressive behavior was necessary to survive.
The behaviors that adults use to establish dominance are learned by the hyenas as cubs in the communal den. Cubs engage in play fighting beginning at an early age with other cubs, subadults, and occasionally adults (Owens & Owens 1979b). This play consists of neck biting, muzzle wrestling, chasing and leg biting. The play often becomes very aggressive, with frequent drawing of blood at the neck. Owens and Owens (1979b) have noted that the largest and most aggressive cubs feed more frequently than other cubs. Therefore, the limited food resources of the central Kalahari select for aggressive individuals at an early age.
In contrast to the brown hyena, the spotted hyena group contains
a female dominant to all other individuals in the group (Frank 1986a).
As mentioned earlier, she is larger than males and has masculinized genitalia.
This dominant female decides who mates with her and controls all feeding
activity. The clan males do not feed until she is done and do not
mate with her until she decides she is ready (Frank 1986b). It is
not fully understood why this is so. Kruuk (1972) suggested that
the female became so masculinized in order to protect her young.
The more likely reason is that intense food competition required highly
aggressive behavior, and those females that survived to give birth to young
were also those that were able to feed more dominantly over others (Frank
1986b).
Social Cooperation and Altruism
There is an extensive system of nonparental aid at the communal brown hyena den. Nonparental helping behavior includes communal suckling, food provisioning, den maintenance, defense against predation, play, and even adoption of orphans (Owens & Owens 1984b). During the first three to four months of their development, brown hyena cubs are frequently visited by their mother, who suckles the cubs (Mills 1983a). As mentioned earlier, the mother moves the cubs to the communal den during the fourth month. After moving the cubs the mother begins to visit them less and less often, staying away on foraging trips for several days (Mills 1983a, Owens & Owens 1979b). Nonparental helping enables her to do this.
When the mother hyena is away from the den other female hyenas will suckle her cubs. This has been observed in all brown hyena clans (Mills 1983a, Owens & Owens 1979b, Owens & Owens 1984b, Mills 1982, Owens & Owens 1996). All lactating females in have been observed to suckle other femalesâ offspring, though they show a preference for their own cubs (Owens & Owens 1979b, Owens & Owens 1984b). In addition, most group members return to the den with food intended solely for the cubs, including closely related males (r=1/4 or more), subadults males and females, and dominant males in southern Kalahari clans (Mills 1983a, Mills 1982). However, immigrant adult males in central Kalahari clans were never observed to provision young (Owens & Owens 1984b). Only individuals genetically related to the hyena cubs have been observed to provision food.
Both authors familiar with the brown hyena suggest that this nonparental aid is a form of kin altruism that enhances the inclusive fitness of the individuals performing the altruistic act (Owens & Owens 1984b, Mills 1983a). Because most individuals in the brown hyena clan are genetically related, nonparental aid will almost always benefit a family member. Interestingly, the dominant adult male of southern Kalahari brown hyena clans, who is usually a grown natal male, provides food regularly to cubs, while the dominant immigrant adult males in central Kalahari clans have never been observed to provide nonparental aid other than group protection (Owens & Owens 1996, Owens & Owens 1984b). There are significant benefits for females who provide nonparental aid. Because females will usually eventually breed and have cubs, it is in their best interest to do all they can to increase the clan size so that those individuals will one day help her and her offspring (Owens & Owens 1984b).
In contrast to the brown hyena, female spotted hyenas do not suckle
other femalesâ young, even though the spotted hyena lives in groups of
closely related female matrilines (Frank 1986b). However, it is possible
that spotted hyenas exhibit social cooperation and possibly even kin selection.
It has been observed that the dominant female will allow other femalesâ
cubs to feed next to her at a kill (Frank 1986b). Because this female
controls who has access to food, it is likely that she is allowing the
cubs of kin to feed. However, the author was unable to ascertain
the identity of the other cubs, so it is not possible to determine whether
or not this behavior is an example of kin altruism.
Summary
Food availability is probably the greatest factor influencing
the structure of the brown hyena clan. The availability of food accounts
for the size of the brown hyena clan as well as the size of the home range/territory
a clan occupies. In addition, the availability of food affects the
mating system at the time, and determines whether individuals will stay
with the group as natal adults or emigrate as subadults to join other clans.
The density of hyena clans within a habitat also determines how much aggression
the individuals will show toward others. The availability of food
has also shaped the practice of kin altruism in the brown hyena clan, which
is probably the most distinct feature of this species. The practice
of nonparental aid that has evolved among the brown hyena is a behavior
that has been carefully molded to its environment. The differences
between the brown and spotted hyena have therefore evolved as a result
of their habitats. The spotted hyena has adapted to an environment
with a plentiful supply of food, which has caused the groups to become
large and the individuals to become aggressive. The brown hyena has
adapted to an environment in which the minimal food supply has caused the
groups to become small and diffuse.
Brown Hyena
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Sources Cited
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