~ This page was made as part of an undergraduate course at Davidson College ~
Social Cooperation
This dwarf mongoose is on alert, keeping a watchful eye out for predators [Photo courtesy of James Warwick].
Why cooperate?
Survival of the dwarf mongoose is dependent on the cohesiveness of the group. Because of predation factors, dwarf mongooses would not be capable of living independently, and they would find it overly difficult to live in a pair. Also, dwarf mongooses need helpers to protect the young while finding food for themselves. By living in a group, they have the added benefit of division of labor. Therefore, it is beneficial to the individual to cooperate within the group, whether your pack members are family or not (Rood, 1978).
What do different pack members do to help?
Pack members baby-sit, feed, groom, and transport young dwarf mongooses. Feeding helpers were usually the younger ones; they bring freshly killed food to young ones greater than or equal to one week old. Age and sex are stronger determinants of for helping behavior than degree of relatedness (Rood, 1978). For example, just because a dwarf mongoose is an immigrant does not mean that it will participate in less cooperation.
How do male dwarf mongooses cooperate?
Subordinate adult male dwarf mongooses are involved in vigilance, with only one male at a time displaying vigilance. Dwarf mongooses have a complex coordinated vigilance system. There are five basic behavioral parameters of vigilance:
1. Selection of an appropriate site to guard from
2. Maintenance of alertness for predators over longer periods of time
3. Vocalization of appropriate warning calls for different predators
4. Correct orientation with respect to the group
5. Relieving other guards in proper sequence
While action patterns of vigilance behavior seem to be innate, all other aspects
of vigilance must be learned. Therefore, vigilance is considered to be a socially
acquired behavior (Rasa, "Behavioural Parameters...").
What would the pack do without these guards?! Efficacy of vigilance is quite high: 93% of raptor attacks are aborted by guards' warning calls and 100% of terretrial attacks are aborted by guards' warning calls (Rasa, "The costs...").
What sort of adaptations do these males have to cooperation?
Male guards have distinct vocalizations to communicate a variety
of different messages to their pack members. Vocalizations relate to degree
of dangerousness, distance from the group and elevation, and combining and modifying
these codes to correlate with changes in predator type and location. They have
a high level of predator discrimination (calls differ significantly among the
predators). In fact, dwarf mongooses are the only currently known non-human
mammal to use recombinations of encoded info into a “language” for
specific predator threats (honey bees are the only other species besides humans
that have as complex a system for information transfer). There are four categories
of warning calls: excitement twitters, panic twitters (both monosyllabic pulsed
or heterotypical sound sequences), ground predator calls, aerial predator calls
(both frequency-modulated calls). Pulsed calls always precede frequency-modulated
calls in syntax. Excitement twitters and panic twitters are used for distance
information (ie, panic twitters begin when predator comes really close). Frequency-modulated
calls are used for elevation information. Why do dwarf mongooses have such a
complex alarm calling system? As discussed earlier, they have all these vocalizations
because there is such a high level of predation from both terrestrial and aerial
animals, and it is critical to foraging because calls minimize hiding time (Beynon
& Rasa).
How do female dwarf mongooses cooperate?
Subordinate female adult dwarf mongooses cooperate in the group by acting as alloparents. They babysit the young while the rest of the pack forages. They even lactate at the same time as the alpha female (despite the fact that they never become visibly pregnant) so that they can provide milk for the newborns. Babysitting in females can be likened to vigilance in males, and both can be attributed to a "caring" tendency (Rasa, "Behavioural Parameters...").
So we see how dwarf mongooses cooperate with each other-- do they cooperate with any other animals?
Funny you should ask! Dwarf mongooses have an interesting symbiotic relationship with a couple species of hornbills in eastern Kenya. In this relationship, hornbills give out warning calls when a predatory bird is in close proximity (even if it is a predator to just the mongooses). Since hornbills eat the same food as mongooses, they benefit from the relationship because the mongoose does all the foraging. Hornbills rarely compete for food with the mongooses and will usually submit to them anyhow. The hornbills and dwarf mongooses wait for each other to begin foraging; if no mongooses are present, the hornbill will call down the den to wake them up. If no hornbills are present, the mongoose will display stress and decreased efficiency of foraging (Postanowicz).
Can the cooperative behavior of dwarf mongooses be described as altruistic?
While there are certain costs to both vigilance and babysitting (guards can be killed in the process of alarm-calling and babysitters do not get a chance to forage food), there are clear benefits to cooperation as well. For example, while a male subordinate is obliged to guard, he does get to switch positions with other subordinate males in the pack. This allows him to forage under the protection of another guard. Also, cooperation in the pack maximizes successful foraging time for the alphas and other subordinate males not guarding at the time. Helpers can therefore increase their individual fitness by helping young which later benefit them. An increase in pack size leads to an increase in protection from predation and and increase in anti-predator responses given. Also, if the helpers become alpha, then the young that they have helped will likely return the favor by helping them raise their young (Rood, 1978).