What is mechanism?

Mechanism is also referred to as causation by Tinbergen. They explain behavior in terms of what the behavior is and how the behavior is performed. These explainations can include physical morphology, ecological context, molecular mechanisms, other underlying biological factors, or external stimuli.

Ecological Context of Sentinel Behavior

Meerkats are not chosen to perform sentinel duties, they "choose" to do so, as shown by Clutton-Brock et al. (1999b). They showed that guarding may be an individual's optimal activity once its stomach is full if no other animal is on guard. They supported their claim by showing that, in in groups of meerkats, animals guard from safe sites, and that most of them spend their time on guard anyway. For the foragers its just simple glances to the left and right. For the sentinel, it asks them to vocalize and to sound the alarm when they spot something that may endanger the group. The guards are obviously not-continual, at the same time there's no specific order. With no individual able to guard for over two hours in one day, the provision of food contributes to guarding,and ables other merkats to stand guard.

Meerkat Babysitter
Figure 2. (A) Meerkats foraging in Kalahari Gemsbok Park. (B) Individuals commonly dig up to 20 cm below ground to find prey and cannot watch for predators while doing so. (C) Digging animals frequently stop to glance around them but do so less frequently if a raised guard is vocalizing. (D) While the group is foraging, one animal commonly climbs a tree or mound and watches for predators. (Clutton Brock et al. 1999b)

Meerkats often forage far away form their burrows, which makes them quite vulnerable to predators and intruders. This is why it is beneficial for them to have raised guards because this will allow the foragers to focus on searching for food without worrying about predation. Without the sentinel, the meerkats would always have to look around at their surroundings to make sure the parameter is clear. Figure 2 depicts the sequence of foraging when a sentinel is present. The sentinel announces its presence by vocalization indicating that they are on guard duty. This allows the foraging meerkats to become less vigilant as a result - less glancing around. The foragers would benefit from being watched for, as now they can search for the most optimal food. When the sentinel sees an enemy approaching, they will call out different kind of alarms depending on the type of predator or intruder they spotted. Their calls will also signal both the type of predator and the urgency of the threat (Manser et al. 2002). Their most common predators are avian predators, ground predators, snakes and meerkat intruders. Overall, guarding is beneficial to the other group members because it allows them to spend less time being vigilance.

There are three types of vigilance: guarding at the ground level while foraging, guarding at the burrow entrances and guarding from a raised position, such as a tree or mound (Tatalovic 2010).

Effect of Oxytocin on Sentinel Behavior

A recent study found that in peripheral administration of oxytocin, a suite of cooperative behaviors (ie. digging, guarding, pup-feeding, and time spent with pups) were enhanced, as seen in Figure3. In addition, initiated aggressions were decreased by oxytocin injection. They also found that early exposure to prosocial behavior such as tactile parental care can in fact influence oxytocin susceptibility in pups in such a way that as adults, they show greater prosocial behavior themselves. Thus, they assert that if this unnatural form of administration operates in a similar way to the natural oxytocin system in each individual meerkat, it could explain aspects of heritability of prosocial behavior in meerkats based on oxytocin receptors, where early parental care can carry over to determine adult behavior. Furthermore, there are still many costs and benefits associated with increase of prosocial behaviors and the consequences these have on other factors affecting reproductive success (Madden 2010).

Figure 3. Individuals' prosocial behaviors following injection with oxytocin and a saline control when guarding. Mean proportions of each activity compared with those of the saline control are shown +1 s.e. (Madden 2010)