Mongooses Pay Back Individuals Who Previously Protected Them
Wild individuals who did more guarding were groomed more than those who hadn't.
Posted May 31, 2018
A research essay titled "Experimental evidence for delayed contingent cooperation among wild dwarf mongooses" by Drs. Julie Kern and Andrew Redford of the School of Biological Sciences at the UK's University of Bristol, published in the prestigious journal Proceedings of the National Academy of Sciences (PNAS), offers novel data on how these small African carnivores pay back individuals who have previously guarded them. While other nonhuman animals (animals) have been observed paying back group members or trading cooperative actions immediately, that's novel about the mongooses is that they pay back other group members who protected them at a later time by offering grooming. As Kern and Redford write, their study provides "experimental evidence of delayed contingent cooperation, and cross-commodity exchange, in a wild nonprimate."
The entire research essay is available online, so here's a summary of this very important field project. An essay called "Mongooses remember and reward helpful friends" is written for a broad audience and offers a concise summary of Kern and Redford's paper. Dwarf mongooses are cooperatively breeding animals who live in stable groups of around 5-30 individuals and are perfect animals on whom to investigate cooperative behavior. Breeding is done by a dominant male and female pair who receives help from other male and female group members. During daylight hours, while foraging, they keep in contact using different vocalizations because the terrain doesn't allow for visual monitoring of one another. While individuals are digging for invertebrate prey, they can't also look out for predators, so the job of protecting them is left to mongooses who serve as sentinels. Kern and Redford write, "Sentinels produce alarm calls to warn of predators and surveillance calls to announce their own presence (34, 39); foragers do not obviously look up when sentinels produce a surveillance call, but they do reduce their personal vigilance and increase time spent foraging in the presence of a sentinel and in response to surveillance-call playback (38)." (Numbers refer to references in their essay.)
To gather data, 12 groups of free-living mongooses who were accustomed to the presence of humans were studied on Sorabi Rock Lodge, Limpopo Province, South Africa. Individuals of known gender were identified by using dye or by using distinct natural markings, and for most of them researchers also knew their age. Between April 2015 and October 2017 grooming behavior was monitored and the grooming data that were used came from a four month period when group composition was stable. Sentinel behavior was also studied between April 2015 and October 2017. The researchers write, "Sentinels were defined as individuals positioned on an object (e.g., termite mound, tree, rock), with their hind feet at least 10 cm above the surrounding substrate, and actively scanning the surroundings while groupmates were engaged in other activities, primarily foraging (38⇓–40)."
The researchers also supplanted direct observations with a novel experiment. Not only were mongooses watched, but also, field experiments were conducted in which the researchers used playbacks of a subordinate individuals surveillance calls—"vocalisations given to announce it is performing this duty."
To gather data on patterns of grooming, mongooses were watched each evening at their sleeping burrow, including those whose vocalizations were "unregulated." Their results were very interesting and important. "On days when an individual was perceived to conduct more sentinel duty, it received more evening grooming from groupmates than on control days (when its foraging calls had been played back during the preceding foraging session). Moreover, the individual who had had its sentinel contribution upregulated received more grooming than a control subordinate in the group."
Sentinel mongooses are paid back later in the day rather than immediately
What is significant about this project is that sentinels were paid back later in the day, rather than immediately after they warned group members of danger. Trading calling for grooming is an example of "cross-commodity trading," and this is the first study to provide evidence of delayed contingent cooperation -- sentinels receiving grooming later in the day -- in a nonprimate mammal.
Please stay tuned for future discussions of the fascinating social behavior of other animals with whom we share our magnificent planet. The more we study, the more we learn. For example, with respect to the current study, while we've learned that mongooses pay back those who guarded them the most, we still don't know if mongooses who received more grooming at sleeping refuges engaged in more sentinel behavior the next day. I hope to see some data that are relevant to this question in the not too distant future.
What's especially interesting and important is that a wide range of nonhumans have been shown to display behavior patterns that previously had been thought to be uniquely human or uniquely "primate." This study clearly shows we need to expand our views about the cognitive capacities of other animals, and we need to be very careful about claiming we're all that unique in certain arenas. These intriguing mongooses and the study being discussed clearly show we're not.