1. Allison, M.L., Reed, R., Michels, E., and Boogert, N.J., The drivers and functions of rock juggling in otters, R. Soc. Open Sci., 2020, vol. 7, p. 200141. https://doi.org/10.1098/rsos.200141
2. Altmann, J., Observational study of behavior: sampling methods, Behaviour, 1974, vol. 49, nos. 3–4, pp. 227–265.
3. Animal Play: Evolutionary, Comparative and Ecological Perspectives, Bekoff, M. and Byers, J.A., Eds., Cambridge Univ. Press, 1998.
4. Borisova, N.G., Popov, S.V., Il’chenko, O.G., Starkov, A.I., and Lenkhoboeva, S.Yu., New data on the spatial and ethological structure of the Turukhan pika (Ochotona turuchanensis Naumov 1934), in Mlekopitayushchie v menyayushchemsya mire: aktual’nye problemy teriologii (XI S’’ezd Teriologicheskogo obshchestva pri RAN). Materialy konferentsii s mezhdunarodnym uchastiem, 14–18 marta 2022 g. (Proc. Conf. with International Participation “Mammals in a Changing World: Current Problems of Theriology” (XI Congress of the Theriological Society of the Russian Academy of Sciences), March 14–18, 2022, Moscow, Inst. Probl. Ecol. Evol., Russ. Acad. Sci.), Moscow: Inst. Probl. Ekol. Evol., Ross. Akad. Nauk, 2022, p. 46.
5. Burghardt, G.M., The Genesis of Animal Play: Testing the Limits, Cambridge, Massachusetts: MIT Press, 2005.