>SOCIABILITY<

In the wild, degus live together in groups consisting of roughly 2-5 females and 1-2 males2 , 107 (strongly female biased22). These groups benefit the degus by allowing them to share a communal territory and its resources5 , 19, and also by decreasing the predatory risk by improving vigilance and alertness5. With this in view, degus living exposed areas may form larger groups than degus living in more covered habitats19, although this remains unclear124. Living in large groups decreases the risk of predation in such areas19 , 124. The social nature of the degu may also be related to their larger body size (compared with less social rodents), as they are more vulnerable to predation124. Burrowing may also have social implications124.

Degus display a very elaborate range of dynamic social behaviours11 , 19 which allow a complex social structure. 'Sociability' involves living with other individuals and interacting with them frequently19. Degus live in a hierarchical society that is based on a system of dominance. This dominance has been shown to be associated with large amounts of head sniffing and head grooming in the degu16 (which further study has found is NOT related to salivary olfactants16).

Wild degus will huddle together during cold weather which reduces energy expenditure through heat loss19. Huddling degus have to produce less energy to maintain thermeostasis than a solitary degu in cold environments. This aspect of group living is critical at cold times of the year19. Degus will also lie close together when sleeping30 , 13.

>TERRITORIAL MARKING<

Degu groups share a feeding range and burrow system2. The burrow is the centre of defended territory52. Individuals belonging to different groups often mix freely19, except during the breeding season when all group members become more teritorial19. Males (particularly dominant males107) will also become less tolerant of other males during this time22 , 32, which is possibly correlated with a peak in testosterone levels, and hence aggression107, during the breeding season32. Males belonging to one group have been observed to show aggressive behaviour toward males of another group, suggesting an element of group territoriality32. Typical male territorial behaviour includes agonistic interactions such as chasing, mounting and foreleg pushing107. The winner is the degu that remains in the conflicted area107. Once territory is established, agnostic interactions between males decline significantly107. Territory is defined by urine scent marks which are visible to degus when fresh as they are highly UV reflective21 , 22 , 24.

Dustbathing is frequently used by all wild degus not only to keep themselves clean, but also as a form of communication. Male degus have been observed to use dustbathing during intrasexual communication22. Both male and females will bathe for longer in a patch of sand previously used by a familiar degu22 , 132, in order to increase the strength of their own scent22 in the sand. In this way, degus are capable of distinguishing other degu's scents from the scent marks they have left22. Scent marks are made when the degu deposits small amounts of urine on the ground132. This is characterised by the degu dragging its ano-genital region along the floor for a short distance132 and often is accompanied by a highly specialised behaviour pattern22 (a 'fixed action pattern'). Such marks are saturated with pheromones, which are highly olfactory chemicals unique in each degu. Such pheromones are left as indicators of sex, breeding status, rank of dominance or territory ownership22 and are also used to create familiarity between group members, increasing group cohesion22. Degus are programmed to deposit and investigate scents17 in order to regulate what is happening in their group. Degus will mark out an unfamiliar area132, an unfamiliar object132, and generally tend to mark over spots marked by other degus132. It has been shown that female degus are more active at responding to scents left by other degus17, as they are more sensitive and sniff scents more frequently than males17. Such scents (or pheromones) may be left in the urine, and research shows female degu urine is sniffed more frequently by both males and females17. Exactly why is not clear, but it is hypothesised that female degu urine may contain more olfactory clues as to what breeding condition she is in. Similar research has found that although males have a lesser sense of smell than females, males can still differentiate between male and female degu urine7. It has been hypothesised that this is useful to males as they can identify opposite sex siblings and avoid contact with them7 in order to prevent inbreeding occurring. It has also been hypothesised that a primary function of male dustbathing is territorial defense, while that of female bathing is group cohesion22. Other sources of pheromones include sebaceous scent glands22 in the hair follicles, and specialised scent glands22.

Degu communication not only involves olfactory cues (scent marks), but also visual (UV reflection), auditory (vocalisation) and tactile (grooming) signals22. Grooming is initiated by presentation of the throat, or moving the head under another degu's chin132, and consists of nibbling the head and fore-body132.

During territorial disputes and agonistic encounters, one or both contenders may perform dustbathing behaviour22.

>TEAM WORK<

Degus living in the same group will often communally dig out a burrow system. Degus work together, forming digging 'chains'2. In these chains, two or three degus will work at the same site forming a line, with each shifting soil out behind them2. Clever! Two animals working together will organise themselves in shifts, with one degu digging and the other on guard outside the entrance2. They will take turns to swap roles, during which time they will vocalise to each other2.

Sharing the digging not only reduces the time taken to create a burrow, but also reduces the amount of energy a degu uses during digging2 , 5. This is one of the reasons degus have evolved to live in groups5.

>REPRODUCTION<

In the wild, most mating activity takes place around the autumn22 , 23 , 28, when there is roughly 12 hours light : 12 hours darkness22. Degus are seasonal breeders28 and usually reproduce successfully only once a year28 , 51 , 52. During the breeding season, males increase their social interactions and this is thought to stimulate a rise in testosterone levels106 , 107. Males follow one of two breeding strategies; resident males belonging to a group will defend his females and mate with them regularly106, while transient males mate whenever the opportunity occurs in various groups106. Conception typically occurs in Chilean late spring23, and again in Chilean early summer23 as a consequence of the post-partum oestrus32. Adult females start to show signs of pregnancy in Chilean early spring28, not long before they are due to give birth. Parturition (birth of pups) occurs in Chilean early spring28 , 32, with lactation lasting until mid-late spring28. The post-partum litter is born in the Chilean late spring to early summer32. This is followed by a non-reproductive period in the Chilean summer28. Juvenile pups appear above ground in late spring28 , 109 when they feed on the fresh grass109. Pups frequently engage in play, and perform 'locomotor rotational movements' (a.k.a. 'frisky hops' or 'popcorning')132 which it is thought helps them to develop anti-predator movements/strategies132. Adults may also be seen to use this behaviour during play132. It is thought that smelling the body of a playmate can induce 'popcorning'132.

Degus communally rear their young and nest in groups of 2-4 adults81 in their underground burrows132. This involves one degu in the group taking care of many pups including the young of other group members (for more information, visit the breeding section). Communal nesting may have influenced the fact that degu pups are born precocious as the degree of their development at birth means they require less suckling than more altricial species23. Mother will therefore need to use less energy producing milk and so reduce the cost of sharing milk with other pups23. However, mother degus will not tolerate unfamiliar female degus from another group near their young and will often give an agonistic vocalisation followed by a chasing event23 to see the intruder off. This behaviour is related to the access of females to cover the pups and is shown to be reduced in females already familiar with each other's company23. This has been further demonstrated to be involved with the relatedness of the degus81, with individuals sharing a nest showing a significantly higher degree of relatedness compared to other group members81. Communal nesting between female kin therefore allows indirect as well as direct fitness benefits for the degus and their offspring81.

An important point to note here is that degus DO NOT commit infanticide19. Unlike hamsters, which are frequently observed to kill and even eat their young when stressed, degus have never been reported to show this maladaptive behaviour19. It has been suggested that degus do not commit infanticide due to phylogenetic inertia32. Male and female unrelated degus do not even show aggression toward unfamiliar pups32.

In communal rearing, lactating females spend the most time socially interacting with the pups32, and unrelated males spend the least time with them32.

Although males generally spend more energy during reproduction, females use more energy to nurse their pups during lactation28. Male degus may compete for females during the breeding season32 and demonstrate 'tail wagging' when aroused; both during courtship and during agonistic encounters132.

The fact that degus have such lengthy gestation times and set breeding periods is not always a good thing. Because of this, wild degus may be under threat due to human disturbance133.

>DOMINANCE<

Male degus collect debris such as twigs, rocks, wood, dung and plants and pile it up into mounds outside the entrance to their burrows30 , 52. The size of the pile indicates the social status (dominance) of that male30 and thus serve as territorial markers52.

After an agonistic encounter, the winning male increases his mound size30 after chasing off the intruder52. Dominance encounters have been found to be related to social stress106, resulting in higher cortisol levels106. Males may present their rumps to one another and attempt to mount prior to aggression132 which may be to 'size each other up'.

If a mound is accidentally destroyed, that male looses all his social status30.

>PROBLEMS<

There are, however, drawbacks to living in groups. Large groups means regular social contact with other degus, which increases the chance of degus catching and passing on parasites and diseases19. If one degu dies of an infection, the whole group could be wiped out very quickly.

If groups get too large, there can be an increase in the number of aggressive threats between group members19. This is largely due to increased competition for breeding partners, living space, territory and food19.

Another form of competition encountered by group living is the chance to mate and pass on genes to another generation. If group numbers become too large, cuckoldry increases19. Cuckoldry is a term used to describe the act of a female mating with more than one male in a group. This will therefore decrease the chances of any one male to pass on his genes to the offspring.

On the whole, however, the advantages must outweigh the disadvantages or group living would not occur at all. It may be these disadvantages that have caused degus to evolve to live in relatively small groups.