1. Ecology
  2. Neuroscience
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The social life of Norway rats (Rattus norvegicus)

  1. Manon K Schweinfurth  Is a corresponding author
  1. School of Psychology and Neuroscience, University of St Andrews, United Kingdom
Review Article
Cite this article as: eLife 2020;9:e54020 doi: 10.7554/eLife.54020
2 figures and 2 tables

Figures

Wild and domesticated Norway rats.

Wild rats (panel [a] depicts two female wild-derived rats) differ from domesticated rats (panel [b] shows two female domesticated rats) greatly in respect to their coat colour but less so in their social life, which is illustrated by domesticated rats showing the full behavioural repertoire of wild rats. Therefore, domesticated rats can be good representatives of wild rats and vice versa.

The social organisation of a rat colony.

Rats are social animals that live in large colonies, consisting of sometimes more than 150 female and male individuals with overlapping generations. Rats of a colony establish an underground burrow system with shared channels and chambers. In these chambers, they commonly huddle together to keep warm and often sleep like this (right chamber at the bottom and left at the top). Females establish their nest in such chambers, where they give birth to up to eight pups (middle chamber at the bottom). Colony members reproduce. Males approach females that respond defensively with sidekicks, if they are not in oestrus (left chamber at the bottom). If she is receptive, several males will copulate with her (two rats in the middle). Rats establish a dominance hierarchy, which is more pronounced in males than females. When rats meet, they inspect each other, whereby subordinate individuals show a submissive posture, crawl under the other or avoid such contacts to prevent conflict. Most conflicts, however occur between rats of different colonies. Fights typically start with a threat posture, followed by fights that are interrupted by standing upright and boxing (two rats outside the burrow system). Most commonly, however, rats show amicable behaviour with colony members. For example, they spend time in close proximity to each other (left side, middle rats) or groom each other (right chamber at the top). Drawings by Michelle Gygax.

Tables

Table 1
Ethogram of individual social behaviours in rats.

Rats show a range of social behaviour, that is behaviours that are directly related to conspecifics, which can be split into socio-positive and socio-negative contexts. The ethogram is restricted to wild rats under natural or semi-natural conditions.

CategoryBehaviourSexDescriptionReference
Socio-positiveAllogroomingFemales and malesOne individual gently nibbles or licks the fur of a conspecific, sometimes with the aid of its forepaws. All body parts of the partner may be cleaned including the tail.Barnett, 1963, p. 77
HuddlingFemales and malesRats lie together with direct body contact, sometimes sleeping.Barnett and Spencer, 1951; Barnett, 1963
Inspecting anogenital regionFemales and malesOne individual sniffs or licks the anogenital region of a conspecific, probably used in the context of recognition.Barnett, 1963, p. 64
NosingFemales and malesOne individual gently pushes another’s flank or neck with its nose.Barnett, 1963, p. 77
Nose-touchingFemales and malesTwo individuals approach each other until their noses come into contact. This possibly serves recognition and may result in socio-positive or negative behaviours.Calhoun, 1979, p. 179
Oral inspectionFemales and malesOne individual sniffs at a conspecific’s mouth. This is most common between mothers and their offspring, but takes place between adults, too.Calhoun, 1979, p. 149
PioneeringFemales and malesOne individual leaves the burrow vigilantly and observes the surroundings for several minutes. Only then will other colony members appear from the burrow.Barnett and Spencer, 1951; Telle, 1966
Play fightingFemales and malesOne individual attacks the nape of its opponent, which the latter tries to defend. Play fights take place only during adolescence.Ewer, 1971; Calhoun, 1979, p. 180
Recognition sniffingFemales and malesOne individual shows enhanced sniffing at colony members and (potentially marked) objects, especially if a stranger entered its territory.Barnett, 1967
Scent markingFemales and malesOne individual rubs the flanks or presses the anogenital region on a surface, sometimes leaving urine droplets on the surface.Landete-Castillejos, 1997
Sharing foodFemales and malesAn individual tolerates a conspecific in its close proximity, sometimes even touching each other, while feeding from the same food resource. Alternatively, one individual drops small food items that can be taken by another. Further, residues in the face or on the paws of an individual can be licked off by another.Barnett and Spencer, 1951; Barnett, 1963, p. 36; Calhoun, 1979, p. 101
Submissive postureFemales and malesOne individual lies on its side with eyes half-closed. This posture is used to ‘greet’ more dominant individuals to prevent fights. Sometimes this posture is combined with ‘crawling under’ (see below).Barnett, 1967
Socio-negativeAggressive groomingMostly malesOne individual pins down a conspecific forcefully while allogrooming it. This is often accompanied by squeaks and run-away attempts of the groomed partner.Barnett, 2001, p. 131
AvoidingFemales and malesOne individual changes its route upon detecting another rat.Calhoun, 1979, p. 179
BoxingMostly malesBouts of fights are typically intermitted by standing upright to box. While boxing, they hit and scratch each other’s face, which is accompanied with raised hair and ears pointing forward.Barnett, 1963
ChasingFemales and malesOne individual runs after a second. This usually precedes fights but can also take place afterwards.Calhoun, 1979, p. 181
Crawling under/walking overMostly malesOne rat crawls under, that is typically the subordinate, or walks over a conspecific, that is typically the more dominant.Barnett, 1963
Direct approachMostly malesAn individual approaches an opponent to attack, often accompanied with urination and defecation and raised hair. Sometimes the individual shows tooth chattering while approaching.Barnett, 1963
FightingMostly malesTwo rats tumble, roll over the ground while holding, kicking and punching each other.Barnett, 1963; Calhoun, 1979
Leaping and bitingMostly malesThe attacker jumps towards the opponent with extended forelimbs and tries to bite usually its ears, limb or tail. Bites are typically very quick.Barnett, 1963
Passage guardingProbably only malesOne more dominant individual stands in a passage and therefore blocks the way of a second. The opponent typically waits until the first moves away or takes a detour.Calhoun, 1979, p. 187
Pushing awayFemales and malesOne individual pushes another with its forepaws or flank to move a conspecific from its current position. Sometimes pushes are accompanied with kicks or swinging the body towards the opponent.Calhoun, 1979, p. 101
Tail quiveringFemales and malesOne individual quivers its tail, which might be shown in various situations like during ‘crawling under’ or shortly before copulation.Steininger, 1950
Threat postureMostly malesAn attacker adopts a posture where the back is maximally arched, all limbs are extended, and the flank is turned to its opponent.Barnett, 1963
Tooth-chatteringFemales and malesOne individual chatters with its teeth while staying immobile, most common after detecting an opponent.Barnett, 1963
Table 2
Overview of studies showing cooperative behaviour in rats.

Rats are highly social animals that have been shown multiple times to cooperate, i.e. one individual benefits one or more other individuals (Sachs et al., 2004). Several mechanisms have been proposed to explain why they cooperate. Domesticated, wild and wild-derived rats of both sex were tested in a variety of tasks, involving various behaviours to measure their tendency to cooperate.

Proposed
mechanism
Cooperative
behaviour
Sex of test
subjects
Origins of test
subjects
TaskReferences
Assessing the other’s need in a helping taskSimultaneous nose-pokingMalesDomesticated
(Sprague-Dawley)
Skinner boxŁopuch and Popik, 2011
Entering one compartment, which leads to food rewardsT mazeMárquez et al., 2015
Donating food by pulling it into the reach of a partnerFemalesWild-derivedBar pulling taskSchneeberger et al., 2012; Schweinfurth and Taborsky, 2018b
Coordination
(acting together)
Coordinating back and forth shuttlingFemales and malesDomesticated
(Sprague-Dawley)
T-mazeDaniel, 1942
Swanson and Schuster, 1987
Domesticated
(S3, Sprague-Dawley and Wistar)
Schuster et al., 1993
Domesticated
(Sprague-Dawley and S3)
Schuster et al., 1988
MalesDomesticated (Long Evans)Tan and Hackenberg, 2016
Division of labour
(sharing of tasks)
Tolerating theftsFemales and malesDomesticated
(Wistar)
Diving for foodColin and Desor, 1986; Krafft et al., 1994; Grasmuck and Desor, 2002
Donating food by pushing down a leverMalesDomesticated
(Sprague-Dawley)
Skinner boxLittman et al., 1954
Empathy
(ability to perceive and care for the emotional states of others)
Or: social contact seeking
Freeing trapped partners by opening a doorFemales and malesDomesticated
(Wistar)
Partner trapped in containerRice and Gainer, 1962
Domesticated
(Sprague-Dawley)
Ben-Ami Bartal et al., 2011
MalesBen-Ami Bartal et al., 2016
Silberberg et al., 2014
Females and malesPartner trapped in a poolSato et al., 2015; Schwartz et al., 2017
FemalesDomesticated
(Sprague-Dawley and Long-Evans)
Partner trapped in containerBen-Ami Bartal et al., 2014
Inequity aversion
(preference of equal outcomes)
Entering one compartment, which leads to food rewardsMalesDomesticated
(Long- Evans)
T-mazeOberliessen et al., 2016
Prosociality
(preference to provide benefits to others)
Entering one compartment, which leads to food rewardsMalesDomesticated
(Long- Evans)
T-mazeHernandez-Lallement et al., 2014, Hernandez-Lallement et al., 2016
Domesticated
(Sprague-Dawley)
Márquez et al., 2015
Reciprocity
(conditional help based on previous received help)
AllogroomingFemalesWild-derivedDirect interactionsSchweinfurth et al., 2017b
Domesticated
(Sprague-Dawley)
Yee et al., 2008
Donating food by pulling it into the reach of a partnerMalesWild-derivedBar pulling taskSchweinfurth et al., 2019: Schweinfurth and Taborsky, 2018a
Donating food by pushing down a leverDomesticated
(Long-Evans)
Skinner boxLi and Wood, 2017
Entering one compartment, which leads to rewardsDomesticated
(Sprague-Dawley)
T mazeSimones, 2007; Viana et al., 2010
Donating food by pushing down a leverFemales and malesDomesticated
(Long-Evans)
Skinner boxLi and Wood, 2017
Donating food by pulling it into the reach of a partnerFemalesWild-derivedBar pulling taskRutte and Taborsky, 2007;
Rutte and Taborsky, 2008; Dolivo and Taborsky, 2015a; Schweinfurth and Taborsky, 2016
Reciprocity between different commoditiesDonating food by pulling und pushing it into the reach of a partnerFemalesWild-derivedBar pulling and lever pressing task
Schwartz et al., 2017
Allogrooming and donating food by pulling it into the reach of a partnerDirect interaction and bar pulling taskStieger et al., 2017; Schweinfurth and Taborsky, 2018c
WarningAlarm callingFemales and malesDomesticated
(Long- Evans and Wistar)
Cat exposureBlanchard and Blanchard, 1989; Blanchard et al., 1991
PlaybackSales, 1991
MalesDomesticated
(Wistar)
Brudzynski and Chiu, 1995

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