The Dwarf Mongoose

(Helogale parvula)

This page was created by Heather Maloney for an undergraduate Animal Behavior course at Davidson College.

Please contact Dr. Case via email if you have and questions or comments: vecase@davidson.edu

Habitat and General Description

The dwarf mongoose lives in east Africa, from Ethiopia and the Serengeti to South Africa.  The climate is a tropical, with a distinct wet and dry season. The dry season lasts from May to October, and then the rainy season begins in November.  The land ranges from savannah, covered with tough grass and scrub, to thick woodlands.  Acacia trees spot the land, as well as other species hardy enough for the climate.  Also dotting the habitat, and crucial to the dwarf mongoose's existence, are termite mounds.  Packs of mongooses live in the ventilation shafts of these huge mounds, sleeping in them at night and using them for protection during the day. 

As the name suggests, dwarf mongooses are the smallest mongoose species.  They are a monomorphic species, with a body length ranging from about 7 to 10 in, and a tail about 6 to 8 in.  They weigh a little more than 11 oz.  Coloration is reddish brown to speckled gray, and the fur is smooth and short.  The average lifespan is about 9 years.

This species lives in family groups, averaging 8 individual per pack.  There is a dominance hierarchy within the packs, based on age; older individuals are dominant over younger ones.  The typical pack includes an alpha pair, 2 to 3 subordinate males, 3 to 4 subordinate females, and 2-3 juveniles.  The alpha male and female are usually the oldest animals, and are the only ones who breed.  Once alpha status is reached it is usually held for life.  The average tenure is about 2 years, but may be as long as 7 (Rood 1983).  Subordinate adults are in charge of babysitting and anti-predator vigilance.

Alpha status can be reach by several strategies.  The most obvious is to stay in one's natal group and wait until all older same sex individuals die.  However, the wait for alpha status is shorter for individuals that emigrate.  These individuals can join packs with a shorter line to the top, or join a pack where the alpha of their sex recently died.  The most difficult way to reach alpha status is by starting a new pack.  This is because the habitat is saturated and predation is so high that small packs are unlikely to be able to find termitaries for dens or watch effectively for predators.

Emigration is high among juveniles, usually occurring around 1 to 2 years of age.  Males and females emigrate individually, and face aggression from same sex individuals already in the pack they are attempting to join.  Emigration is advantageous because it increases an individual's opportunity to reach breeding status, and decreases inbreeding.  In a study done by Keane, Creel, and Waser, they found that juveniles were more likely to emigrate if they were closely related to the alpha male.  Regardless of emigration, however, they also found no evidence of inbreeding depression (1996).  

Dwarf mongooses share the area with many other species, and as such suffer high predation.  They are preyed on by snakes, jackals, and birds of prey.  The termite mounds provide protection from the latter two predators, but snakes can penetrate the dens, forcing the pack to flee. Fortunately for dwarf mongooses, they have reflexes faster than that of the snake, allowing them to escape attacks.  Contrary to popular belief, mongooses are not immune to snake venom, but they do have a high tolerance for it.

The diet of dwarf mongooses includes mostly insects, but also includes small vertebrates like mice, fruits and berries.  The types of insects eaten are grasshoppers, beetles, termites, and spiders.  Food is plentiful, but scattered and not predictable, and as such is not defended.  Dwarf mongooses forage every day within their territory for whatever insects they come across.  They do not use regular foraging paths, but rather wander wherever seems good at the time (Rasa 1989).

Social Spacing

Dwarf mongooses live on classical territories, which, by definition, are defended from other packs. Territory size depends on pack size, and determined by termite mound distribution. The larger the pack, the larger the territory. They can range from 85 to over 240 acres, and may include hundreds of termite mounds. Waser et al. found that the most successful packs had a median of 175 termitaries/km² (1995).

Territoriality is the result of the high predation pressure. The defended resource for dwarf mongooses are the termite mounds, used for protection and vigilance. They scent mark their territory as they go from one termite mound to another, marking when they arrive and before they leave in the morning. Scent marking is done with cheek and anal glands.  All members of the pack contribute to scent marking, doing it in order of dominance. First, individuals will rub their cheeks from nose to ear, and after scent by dragging their anal glands against the object.  If one pack comes across another pack on their borders the larger pack chases the others off. However, termite mounds on the borders of territories may be used by more than one pack, based on whoever gets their first (Estes 1999).

Mating System

Dwarf mongooses breed in monogamous pairs.  Within a pack there is only one breeding pair, the alpha male and alpha female.  All other adults are reproductively suppressed.  The mating season is between November and May, during the rains.  During this time all females come into estrus synchronously, but only the alpha female becomes pregnant.  She will have 2 to 3 litters in a season, with 2 to 4 young per litter.  Gestation is 5 weeks long, and weaning is 6 weeks after parturition.

During the alpha female's 4 day estrus period the alpha male will hoard her for the first few days.  Only the alpha male copulates with the alpha female during this time.  Meanwhile, the subordinate males copulate with subordinate females, although the alpha male may try to interrupt them.  After a few days, the alpha male may lose interest in the alpha female and copulate with beta females.  If the opportunity arises, beta males will take this time to copulate with the alpha female.

Ultimately, however, the alpha male and female are the only individuals to produce offspring.  Occasionally a subordinate female will become pregnant, but this is rare and the pregnancy is not carried to term.  Although dwarf mongooses become sexually mature at about one year, they are kept from breeding by behavioral and endocrine mechanisms.  Males are suppressed behaviorally by low mating rates due to increased aggression from the alpha male.  Male aggression increases threefold during the mating season.  The higher ranking males will usually start fights, thus reducing the mating rates of subordinates (Creel 1992).  Females are suppressed by a combination of behavior and endocrine mechanisms.  First of all, subordinate females have lower baseline level of estrogen compared to the alpha female.  Then, because subordinate males are kept at low mating rates, the subordinate females have low mating rates.  Subordinate females will accept mounts from males of any rank, but it is inhibited by male-male interactions.  Ovulation in female dwarf mongooses is thought to be induced by mating, therefore if the females have low mating rates, they are kept from ovulating.  Despite all this, non-breeding members of the pack help care for the young by babysitting, transporting, grooming and feeding.  Closely related subordinate females may even spontaneously lactate (Creel 1991).

This mating system has developed because of predation pressure.  Pack size is crucial for survival, and the help of subordinates is necessary to ensure that the pack is protected. The more young a pack can raise, the higher their survival rate will be.  The habitat is so densely populated that it is hard for subordinates to leave and form new packs.  Also, the cost of anti-predator vigilance for a small group is very high, and affects foraging efficiency.  Therefore, it is better to wait in the safety of a pack and help raise the young until one can reach alpha status in an established territory.

Altruism

Dwarf mongooses exhibit altruism within their packs.  It can be categorized as a combination of kin selection and reciprocal altruism for the following reasons.  Dwarf mongooses live in family groups with a single, monogamous breeding pair.  This alpha pair produces all of the offspring, who are then raised cooperatively by the subadults in the pack.  The altruistic behavior includes feeding, babysitting, transporting, grooming, and watching for predators.  The subordinate females perform most of the babysitting, while subordinate males keep vigilance.  Vigilance during foraging is a highly coordinated effort, requiring at least one guard at all times.  The workload is shared evenly among subordinate males, with guard changes about every 20 minutes (Rasa 1989).  The guards use several warning calls to tell where a predator is coming from, how close they are, and how potentially dangerous they are.  Dwarf mongooses suffer high predation pressure, and therefore larger packs offer more protection to each other.  By helping to raise the young, subadults increase the survival rate of the pack.  This works to the advantage of closely related, subordinate pack members because they are raising brothers and sisters that share ¸ of their genes, or half-brothers and -sisters that share ¹ of their genes.  The fact that only one pair breeds in a pack means that younger individuals may not breed for a while, if at all, so in the meantime it behooves the related subadults in the pack to care for younger siblings. 

However, adding to the complicity of the situation is the fact that emigration is high in both male and female dwarf mongooses, as mentioned earlier.  Why, then, would these non-related subadults put in time caring for the young?  They do it because of reciprocal altruism.  By emigrating to another pack, individuals increase their chance of reaching breeding status at a younger age than those individuals who remain in their natal pack.  And because of predation, it is safer to join another established pack than to attempt to start a new, smaller pack from scratch.  Once an individual has joined a new pack, and increased their opportunity for alpha status, it is advantageous to help raise young and increase pack size in order to increase the survival rate of the new pack.  Back in their natal pack there are sure to be immigrants helping to raise the young there.  This situation fits the reciprocal altruism model proposed by Trivers because emigration is so common that all individuals are faced with many altruistic situations, and the opportunities for others to do the same are symmetrical.  The cost of caring for unrelated young is paid back when immigrants to one's natal group reciprocate, and when they reach alpha status quicker in the new pack and begin breeding themselves.  Then new immigrants continue the reciprocal altruism by caring for the alpha pairs litter. 

A Day in the Life of...

The pack sleeps together in the termite mound, huddling together to conserve body heat.  In the morning, one guard will start lookout before the rest of the pack leaves the den. The pack scent marks the mound and surrounding area, as described above, and then continues to socialize for awhile.  During this time mongooses will groom each other, play and wrestle.  The young will also be fed during this time.  The alpha female initiates pack migration, and the rest follow.  They forage throughout much of the day, moving from termite mound to termite mound.  The subordinate males keep watch the entire time from lookout points on the tops of mounds, or in trees.  Subordinate females help babysit the young and carry them from mound to mound.  Over the course of the day the pack will travel about 1 km.  When they arrive at the den site for the night, they will again spend time grooming each other, socializing and scent marking.  Then it's back to bed to rest up for another day of foraging.

References

Creel, S., Creel, N., Wildt, D.E., Monfort, S.L. (1992). Behavioural and endocrine mechanisms of reproductive suppression in Serengeti dwarf mongooses. Animal Behaviour 43, p.231-244.

Estes, R.D. (1999). The Safari Companion. Rev. Ed. White River Junction: Chelsea Green Publishing Company, 459 pgs.

Creel, S.R., Monfort, S.L., Wildt, D.E. (1991). Spontaneous lactation is an adaptive result of pseudopregnancy. Nature 351, p.660-662.

Keane, B., Creel, S.R., and Waser, P.M. (1996). No evidence of inbreeding      avoidance or inbreeding depression in a social carnivore. Behavioral Ecology 7, p.480-489.

Rasa, O.A.E. (1989). Behavioural parameters of vigilance in the dwarf mongoose: social acquisition of a sex biased role. Behaviour 110, p.125-145.

Rood, J.P. (1983). The social system of the dwarf mongoose. In: Advances in the Study of Mammalian Behavior (Ed. by J.F. Eisenberg and D.G. Kleiman), p.454-489. Shippensburg, PA: American Society of Mammalogists.

Waser, P.M., Elliott, Creel, S., Creel, N. (1995). Habitat variation and mongoose demography. In: Serengeti II (Ed. by A.R.E. Sinclair and P. Arcese), p.420-448. Chicago: University of Chicago Press.