Table 1.

Sex differences in the frequency and type of play across multiple mammalian species

Species Studied	Sex with Higher Play Frequency	References	Additional Notes
Humans	Males	Whiting & Edwards, 1973; DiPietro, 1981; Humphreys & Smith, 1987
Rats	Males	Poole & Fish, 1976; Olioff & Stewart, 1978; Meaney & Stewart, 1981b	The sex difference is most robust in same-sex dyads and least robust when highly motivated, i.e. preceded by a period of social isolation
Cats (domestic)	Males	Caro, 1981	Males from all-male groups play at higher frequency than females from all-female groups; male play frequency was not influenced by the number of opposite-sex playmates while female play is affected by the number of male playmates
Dogs (domestic)	Males	Pal, 2008; Ward et al., 2008	In mixed-sex dyads, males also engaged in offensive behaviors and self-handicapped more than females (Ward et al., 2008)
Horses (domestic)	Males	Crowell-Davis et al., 1987
Pigs (domestic)	Males	Dobao et al., 1987; Brown et al., 2018; Weller et al., 2019
Cattle (domestic)	Males	Reinhardt et al., 1978	Additionally, both sexes prefer to direct play behavior toward male calves
Sheep (domestic)	Males	Sachs & Harris, 1978
Sheep (wild)	Males	Hass & Jenni, 1993	Male lambs also exhibit a larger repertoire of play behaviors than females
Siberian ibex	Males	Byers, 1980
Sea lions	Males	Gentry, 1974	Male pups also exhibit a larger repertoire of play behaviors than females
Yellow-bellied marmots	Males	Jamieson & Armitage, 1987; Monclús et al, 2011	Females with larger anogenital distances (i.e. masculinized females) engaged in play more frequently than females with smaller anogenital distances (Monclús et al., 2011)
Belding squirrels	Males	Holekamp et al., 1984
Rhesus monkeys	Males	Goy & Deputte, 1996	Sex difference in frequency is based on a sex difference in play initiations (males > females)
Squirrel monkeys	Males	Biben, 2010	Male play bouts are also longer than female play bouts
Lowland gorillas	Males	Meder, 1990
Baboons	Males	Owens, 1975
Spotted hyenas	Females	Pedersen et al., 1990	Females of this species are dominant to males, are larger than males, and have external genitalia. Speaking to these observations, adult females also have higher levels of circulating testosterone relative to males than is typically seen in female mammals.