SOCIAL RELATIONSHIPS
Courtesy of Marko Laakkonen
Mating System
Banded mongooses possess a cooperative breeding system (also known as polygynandry) in which mating occurs between several breeding males and females within the pack. Unlike promiscuity, these groups of mating individuals become bonded over time. Reproduction is synchronized within the social group. Dominant females come into oestrus about 10 days after parturition, usually a few days prior to subordinate females. Pack oestrus lasts for about 6 days. The delayed oestrus of the younger females may be a result of them responding to behavioral or pheromone cues given off by dominant females rather than younger females purposefully delaying mating for other reasons. It is not probable that younger females delay mating in order to get a chance to mate only with dominant males since females were seen to engage in copulations with subordinate males as well. Delaying oestrus to mate with dominants for purposes of preventing infanticide is also not a likely explanation, since there has only been one known instance of infanticide performed by members of the same pack (Cant, 2000). During the oestrus period, dominant males guard the oldest females, but may not always be successful at their attempts. Once the dominant males mate with the oldest females, they guard and mate with the younger females. Females begin to shown signs of pregnancy after a few weeks. The average gestation period is 62 days. Despite the slight difference in timing of oestrus, all females give birth in the same den on the same day (Cant, 2000). The pack uses the natal den for approximately 7 days before moving to a new den (Cant, 2002). Females in a pack give birth about four times a year (Cant, 2004).
In a study that collected data on “mounting attempts”, “mate guarding”, and “pack oestrus”, it was found that dominant males (26% of males) mate guard females while they are in oestrus. During mate guarding, males follow females closely for most of the day. Other males are prevented from accessing the female through snaps, lunges, and pounces. There are fewer females in a pack than males; therefore, males have to put in a lot of effort in order to ensure reproductive success. Despite the dominant males’ attempts to monopolize access to reproduction, females oftentimes increase copulations with subordinate males by escaping from the mate guards or by refusing a greater proportion of the dominant males’ mounts than those of others. Females do not attempt to prevent the mating attempts of other females. Since all females give birth on the same day, older females gestate for a longer period of time than younger females. Younger females tend to have smaller litter sizes than older females (Cant, 2000).
Why this type of mating system?
A polygynandrous mating system gives banded mongooses a couple of advantages. By maximizing mating encounters with males, females increase their likelihood of obtaining the “best genes”. This strategy also increases heterozygosity among the offspring. Furthermore, the effort that males put into mating with females increases the paternal investment in the offspring, which may result in higher quality care of young. Because there is a greater male to female sex ratio, females have more opportunities for mating than males. Males have to put in effort, through mate guarding (for dominant males) or sneak copulations (for subordinate males) in order to mate with females.
Dominant females did not engage in reproductive suppression because it would require a large expenditure of energy and would not incur any additional fitness benefits. After all, banded mongooses have low ecological restraints. According to Cant, females did not suffer reduced direct fitness by allowing subordinates to mate. In fact, pup survival rate increased with increasing number of females who gave birth. Increased survival rate may be due to the predator dilution that results from large litters. At some point, however, increased competition may outweigh the benefits obtained from lack of reproductive suppression. Therefore, it may be advantageous to allow only some closely related females to reproduce (Cant, 2000).
As mentioned, living in packs increases the survival rate of of all members in many ways. A cooperative breeding system is just another strategy that banded mongooses have adapted due to their living situation. By having multiple breeding males and females, the group can insure heterozygosity and the passing on of "good genes". Because mating requires males to put in a lot of effort or risk through mate guarding and sneak copulations, males in the group will have more parental investment in the offspring. The unknown paternity of the offspring allows the members in the group to care for all offspring equally well. All of these components lead to the communal raising of young. By raising the young communally, each pack members can utilize their energy efficiently because only one or two mongooses are necessary to guard the young while the rest of the group forages. As a result, all members of the pack benefit this form of mating system.
Male/male and Female/female interactions
There is not much information regarding any specific male/male and female/female interactions, probably because banded mongooses live in a relatively egalitarian social system (de Luca and Ginsberg, 1999). Same sex interactions are most prevalent during mating season. When a female comes into oestrus, the dominant male prevents other males from coming near their guarded female by following her around for most of the day and displaying agonistic behavior such as snapping, lunging, and pouncing. Females do not prevent other females from accessing mates (Cant, 2000). When evictions take place in times of scarce resources, males tend to act aggressively towards both sexes, while females only attack other females within the pack (Cant et. al., 2001).
Parent/offspring Interactions
Almost all of the adults in the pack care for the offspring in the group by either babysitting or escorting the young. During babysitting, a pack member stays behind to protect the young while the rest of the pack forages in the morning or afternoon. Usually, a different member baby-sits during each session. In a 32-day observation of a group of tagged mongooses, Rood observed that males typically stayed behind to guard the pups while females and the rest of the group leave to forage. From these observations, males participated in pup guarding 73% of the time while the females participated in the remainder of the pup guarding. Lactating females were never observed to pup guard at all (Rood, 1974). According to Cant, however, dominant males, subordinate males, and breeding females all contribute the same share of responsibility to babysitting, although subordinate males baby-sit mostly in the morning during the most energetically costly time of time. Subordinate males also baby-sit more than dominant males and breeding females during oestrus (2000). In some cases, a subordinate male known as a "superbabysitter" takes on an overwhelming amount of babysitting responsibilities. Care of pups is unique in banded mongooses because it is provided predominately by males, which is unusual in most mammals. Pup guarding contains an adaptive significance because pup survival increases when there is an adult around to deter predators (Rood, 1975). In fact, the survival rate of pups increases with an increase in the number of babysitters guarding the young (Cant, 2002).
When a pup is old enough to leave the den, it develops a relationship with an adult member in the pack. That member then provides guidance and assistance to the pups as it grows up and becomes more experienced. One study focused on how banded mongoose actively care for pups, determined whether pups benefit from association with an adult escort, and whether the escort or pup is responsible for maintaining the association. Observations were made of the interactions between pups (0-90 days old) and adults (greater than 364 days old) on the Mweya Peninsula of Queen Elizabeth National Park, Uganda. The adults cared for pups by carrying, provisioning with food, grooming, and playing with the pups. Adult escorts provisioned for pups more often than non-escorts. Non-escorts were typically sub-adults (183-364 days old); indicating that the difference in caring for pups may be due to greater energetic costs or lower foraging efficiency relative to adults. The pups consistently followed the same single escort and defended its association from other pups though aggression, indicating that a single escort provided sufficient provisions and that defense of its escort increased the likelihood that the pup would be provisioned by the escort. Protection of an escort to create stable associations may be a means to minimize pup-pup aggression within the group and to ensure that the most dominant pup gets a “good” escort. Escorting did not provide significantly greater benefits to pups in regards to size, condition, or parasite load; however, it did provide the pups with higher survival rates due to better protection from predators and decreased risk of being lost from the group (Gilchrist, 2004).
The level of investment put into caring for young differs slightly between individuals in a pack. In regards to babysitting, the greater investment by the subordinate can be explained in two ways: by kin selection or energetic costs. Over several breeding seasons, the identity of dominant males and breeding females stabilizes over time. As a result, young subordinate may be either full or half siblings to young offspring in the group. Therefore, the subordinate male that sacrifices feeding in order to stay behind and baby-sit may actually incur substantial kin selected benefits. However, it is difficult to explain why some subordinates become “superbabysitters”, since they probably have the same level of relatedness to the offspring as other subordinates in the group. In these case, the “superbabysitter” may possess characteristics that make it less energetically costly to remain behind and care for the young, such as age or nutritional condition. The improved condition of the subordinate may enable it to lose less energetically from babysitting than other subordinate males in the group (Cant, 2002).
In escorting, it is unlikely that escorts preferentially care for kin since pups tend to be the ones initiating contact and maintaining the association with the adult escort. Escorts show no preference toward provisioning care toward a particular pup on a particular visit because they simply feed the closest pup. The communal breeding in banded mongooses makes kin recognition difficult. Nonetheless, pup escorting provides fitness since groups usually consist of relatives. Therefore, escorts may gain future direct fitness benefits by increasing the size and work-force of the group (Gilchrist, 2004).
Interpack encounters
Encounters between packs are highly aggressive. Banded mongooses leave scent markings as they travel throughout the home range so that other packs in the overlapping home range can avoid the area. Packs, however, would oftentimes still come across one another and fight, especially when females are in oestrus. One study of 14 packs in Queen Elizabeth Park, Uganda focused on determining the frequency of encounters between neighboring groups and whether these encounters were associated with the reproductive status of the females. They found that the rate at which packs found each other and fought increased when females of either group were in oestrus. While in oestrus, females would oftentimes stray or lead a pack into the vicinity of another group. The meeting between two groups would then result in intense fighting between packs.
Fighting between groups occurs when extra-group copulations take place at encounters. Extra-group copulations take place when (1) neighboring groups encounter each other due to the overlap of their groups, (2) males from one pack intrude into the home range of another pack, or (3) when females lead their packs into others home ranges and mate with the males there. Both males and females seek extra group copulations. Males mate with females outside their pack to increase their reproductive success. It is, however, uncertain why females engage in extra group copulations because the female would not necessarily gain better genes through these copulations than with the males within her group nor would she be able to prevent infanticide from other groups since there are too many males in the pack to mate with them all. Another explanation why females participate in extra group copulation would be that females want to increase her level of heterozygosity among the offspring and to avoid inbreeding.
| General Description | Habitat and Habitat Utilization | Social System | Social Spacing | Social Relationships | Social Cooperation | Summary | References |
* This web site was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2005