Table 2.

Descriptions of gorilla MSR studies

Study	N	Summary of methods	Findings
Studies employing the Mark test
Lethmate (1974)	6	Extended exposure to mirror for 6 gorillas; 4 individuals mark-tested	Mirror: 2 gorillas used mirror while picking teeth or manipulating other body part. Mark test: 2 of 4 gorillas tested exhibited self-recognition
Suarez and Gallup (1981)	4	1 male (19 years) and 3 females (13, 17 and 18 years); 16 days × 5 h mirror exposure; marked under anaesthetic; 30-min baseline no mirror and 30-min mirror observations after marking	Mirror: viewing and social responses decreased; no self-directed behaviours. Mark test: no mark touching, despite showing interest in control marks on wrists
Ledbetter and Basen (1982)	2	1 male (10 years) and 1 female (11 years); 400 h of exposure to mirrors; marked under anaesthetic; 15-min baseline no mirror and 15-min mirror observations after marking	Mirror: social responses decreased; no self-directed behaviours. Mark test: no mark touching
Parker (1994)	6	Adult male and female in group of six; 17–41-min sessions of mirror exposure	Mark test: 1978: Female Pogo (inadvertently marked by self) and male Bwana (marked by author) both wiped off marks while looking in mirror, the latter with a tool; 1989: self-directed behaviour
Patterson (1978); Patterson and Cohn (1994)	2	Anecdotal accounts of Koko and Michael when exposed regularly to mirrors; mark test without anaesthesia	Mirror: mirror-guided self-directed behaviours from 3.5 y; self-grooming and putting make-up and accessories on in front of a mirror; photographing her mirror image. Mark test: self-directed and mark-directed responses
Evans (cited in Swartz and Evans, 1994)	1	Single male (King, 22 years); marked by keeper	Mark test: self-directed behaviour (but no baseline); touched mark and smelled fingersa
Swartz and Evans (1994)	2	1 male (Etoumbi, 14 years) given 80 h of mirror exposure and 1 female (Zoe, 5 years) given 12 h of mirror exposure; 1-h mark test	Mirror: decreasing interest; Mark test: self-directed behaviour, no mark touching
Nicholson and Gould (1995)	1	Single female (Muke, 26 years) trained to find stimulus only visible in mirror	Mirror: interest; Mark test: self-directed and mark-directed behaviour
Shillito et al. (1999)	2	Subjects: 1 male (Mopie, 22 years) and 1 female (Mandara, 12 years, with 4 years of prior mirror experience) Expt 1: given 15–17.5 h of angled mirror exposure; sham-marking for mark test	Expt 1 Mirror: little mirror interest, no body exploration using mirror; Mark test: no self-directed or mark-directed behaviour
Shillito et al. (1999)	2	Subjects: 1 male (Mopie, 22 years) and 1 female (Mandara, 12 years, with 4 years of prior mirror experience) Expt 2: given additional approx. 9 h of normal mirror exposure; sham-marking for mark test	Expt 2 Mirror: some mirror interest; Mark test: Mandara touched marked brow but not while looking in mirror
Shillito et al. (1999)	2	Subjects: 1 male (Mopie, 22 years) and 1 female (Mandara, 12 y, with 4 years of prior mirror experience) Expt 3: given additional approx. 4 h of normal mirror exposure; sham-marking for mark test, no human presence, recorded by video	Expt 3 Mark test: both gorillas touched marked brow but not notably more so in presence of mirror
Shillito et al. (1999)	2	Subjects: 1 male (Mopie, 22 years) and 1 female (Mandara, 12 years, with 4 years of prior mirror experience) Expt 4: marked on wrist as control	Expt 4 No mirror; Mark test: both gorillas showed interest in wrist marks
Shumaker and Swartz (2002)	1	Single male (Mopie, 25 years); trained to remove dots from enclosure and self, then to touch a laser dot	Mark test: used mirror to guide hand to remove dot sticker and to touch laser spot
Posada and Colell (2007)	1	Single male (Xebo, 17 years); 28 h exposure to mirror; marked by keeper; 30-min no mirror baseline after marking and 45-min mark test observation with mirror	Mirror: interest; no agonistic behaviour; ‘self-referred’ action (including new body postures) and ‘pulling face’ responses. Mark test: no baseline self-directed action; touched mark first away from mirror, smelled fingers, then touched mark in front of mirror and smelled fingers; immediately wiped away control marks
Allen and Schwartz (2008)	1	Single male (Otto, 45 years); 22.5 h exposure to mirror; marked by keeper; 5 × 30-min sham mark trials; 3 × 30-min paint test trials	Mirror: no clear details. Mark test: found mark ‘accidentally’ when touched a water bottle to face and transferred paint to bottle; mirror-mark-directed behaviours in test trials but not sham trials; some mirror-guided behaviour
Studies not employing the Mark test
Yerkes (1927)	1	Anecdotal description of response of female mountain gorilla, Congo (5 years), to mirror	Congo described as showing interest, touching glass, looking and feeling behind mirror
Hoyt (1941)	1	Anecdotal description of response of home-reared gorilla, Toto, to mirror	Toto described as preening herself and examining teeth, but also attacking mirror
Benchley (1944)	2	Anecdotal description of response of mature zoo-living mountain gorillas (Mbongo and Ngagi) to reflection in pool	Gorilla described as displaying and splashing water
Riopelle (1970)	2	Anecdotal account of albino gorilla, Snowflake, and another gorilla, Muni, both aged 6 years, when exposed briefly to mirrors	Mirror: Snowflake fled and then beat on his reflection with bared teeth (social response); Muni “…examined parts of his body that he cannot ordinarily see.” (p. 500) = self-directed behaviour
Law and Lock (1994); Murray (2020)	4	2 males (5 and 26 years) and 2 females (17 and 26 years) each presented with approx. 30 min of video stimuli, including presentation of recorded and live self-images	Video: self-directed behaviour, notably from one juvenile male (included looking inside mouth)
Inoue-Nakamura (1997)	1	Single female (12 years); 25-min exposure to mirror	Mirror: self-directed behaviours

^aOne of the authors (GG) has seen the video upon which this claim is made, and is unconvinced that it shows evidence of mirror-mediated mark-directed behaviour