Social or single mongoose appeal
Social or single mongoose appeal
By : Pete Laver, PhD
NRF Post-doctoral Fellow, Department of Anatomy and Physiology, Faculty of Veterinary Science, University of Pretoria
Group-living is a good anti-predator strategy for several reasons. One reason is the ‘dilution effect’ – if you’re in a crowd you become less likely to be picked out by a predator. Another reason is the improved vigilance of groups. This is the ‘many eyes effect’ – the more pairs of eyes looking out for predators, the more likely the group is to spot danger.
Most animals incur a cost for this vigilance; when an animal scans for predators it misses out on feeding opportunities and may be at higher risk of predation by standing in an exposed vantage point. In the relatively egalitarian social system of banded mongooses this missed opportunity cost is reduced for each individual by all group members taking turns at scanning for predators (typically by standing or sitting upright on their hind legs).
In a similar way, adult male banded mongooses will act as escorts for pups until the pups are old enough to forage efficiently and fend for themselves. A more extreme approach is adopted by dwarf mongooses (and meerkats) where some individuals tend to shoulder more responsibility as sentinels than others. Here, dominant individuals accrue the greatest benefit from this division of labour.
Some group-living species also have well-developed communication systems for alerting group members of threats. They may have different warning calls for aerial versus terrestrial predators. These communication systems may also play a major role in potential mutualisms with other species. For instance, dwarf mongooses in the Taru Desert, Kenya, forage with two species of hornbill.
Both the mongooses and the hornbills forage on approximately the same prey and share some of the same predators. The mongooses disturb invertebrates while foraging, which the hornbills then feed on. The birds produce alarm calls for raptors that prey on both hornbills and mongooses as well as raptors that only prey on mongooses.
As a result, the mongooses reduce their vigilance and increase their foraging efficiency when the hornbills are with them. Banded mongooses appear to adopt a similar association with baboons – often moving and foraging with a baboon troop, supposedly taking advantage of the increased vigilance provided by the baboons.
Group-living also allows small animals to punch above their weight through their ability to mob a predator as a group. Banded mongooses form a seething mass as they group together to confront foe (a predator or a rival mongoose group), running in place, rocking back and forth, jumping over one another. In some extreme cases, banded mongooses have been documented climbing trees to rescue a group member from a martial eagle, and similar successful rescues are also documented in dwarf mongooses. To label these group-living species as ‘creeping’ belies their intriguing behaviour.
In all of the mongoose species (solitary or sociable) in our area, scent is vital for both communication and foraging. In solitary species, scent may be important in finding mates and in marking and defending territories. Similarly in sociable species, scent-marking may maintain social bonds and assist in territory defence. Most mongooses will thus scent mark novel objects in their territories or one another using anal glands (all species) and cheek glands (dwarf, banded, slender, water, yellow). They also tend to defecate in regularly-used latrines.
Most species are predominantly insectivorous and use scent (and sometimes hearing) to locate invertebrate prey. However, mongooses are generally opportunistic predators and will also prey upon birds, small mammals, snakes, lizards and frogs. Some species scavenge carrion such as road kill (eg: slender, white-tailed, banded). Banded mongooses in particular are often struck by cars as they scavenge frogs and snakes squashed on tar roads.
The species that tend towards a more carnivorous diet and take larger vertebrate prey are the large grey mongoose, the water mongoose, and sometimes the slender mongoose. The large grey mongoose was known in ancient Egypt as ‘Pharaoh’s rat’ and its other name ‘ichneumon’ is Greek for ‘tracker’, supposedly for their penchant for digging out and eating crocodile eggs.
Mongoose activity pattern and habitat preferences will often be associated with their foraging and social behaviour or vice versa. For instance, the nocturnal Meller’s mongoose will eat a variety of prey, but appears to feed mostly on termites (some species of which are also nocturnal because they cannot tolerate direct sunlight). Similarly, the water mongoose, which is usually found near rivers, streams, wetlands and dams (but can forage away from water), preys heavily upon crustaceans and amphibians.
Solitary species tend to be nocturnal when the threat of predation by raptors is lowered. Group-living species tend to be diurnal when sight-dependent vigilance offsets the increased predation risk, visual foraging cues are more effective, and group cohesion can be maintained through visual cues.