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.

Category	Behaviour	Sex	Description	Reference
Socio-positive	Allogrooming	Females and males	One 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
	Huddling	Females and males	Rats lie together with direct body contact, sometimes sleeping.	Barnett and Spencer, 1951; Barnett, 1963
	Inspecting anogenital region	Females and males	One individual sniffs or licks the anogenital region of a conspecific, probably used in the context of recognition.	Barnett, 1963, p. 64
	Nosing	Females and males	One individual gently pushes another’s flank or neck with its nose.	Barnett, 1963, p. 77
	Nose-touching	Females and males	Two 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 inspection	Females and males	One 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
	Pioneering	Females and males	One 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 fighting	Females and males	One 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 sniffing	Females and males	One individual shows enhanced sniffing at colony members and (potentially marked) objects, especially if a stranger entered its territory.	Barnett, 1967
	Scent marking	Females and males	One individual rubs the flanks or presses the anogenital region on a surface, sometimes leaving urine droplets on the surface.	Landete-Castillejos, 1997
	Sharing food	Females and males	An 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 posture	Females and males	One 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-negative	Aggressive grooming	Mostly males	One 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
	Avoiding	Females and males	One individual changes its route upon detecting another rat.	Calhoun, 1979, p. 179
	Boxing	Mostly males	Bouts 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
	Chasing	Females and males	One individual runs after a second. This usually precedes fights but can also take place afterwards.	Calhoun, 1979, p. 181
	Crawling under/walking over	Mostly males	One rat crawls under, that is typically the subordinate, or walks over a conspecific, that is typically the more dominant.	Barnett, 1963
	Direct approach	Mostly males	An 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
	Fighting	Mostly males	Two rats tumble, roll over the ground while holding, kicking and punching each other.	Barnett, 1963; Calhoun, 1979
	Leaping and biting	Mostly males	The 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 guarding	Probably only males	One 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 away	Females and males	One 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 quivering	Females and males	One individual quivers its tail, which might be shown in various situations like during ‘crawling under’ or shortly before copulation.	Steininger, 1950
	Threat posture	Mostly males	An 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-chattering	Females and males	One individual chatters with its teeth while staying immobile, most common after detecting an opponent.	Barnett, 1963