Abstract and Summary

The time and energy costs of play behaviour were assessed empirically for 10‐ to 12‐week‐old kittens (Felis catus), using a variety of methods. Play was found, on average, to occupy 9% of total time. The net daily energy expenditure (in excess of resting metabolism) due to play was found to account for approximately 4% (and at most 9%) of total daily energy expenditure, excluding growth. These results cast some doubt on the assertion, commonly found in the behavioural literature, that play is very “costly” and must, therefore, have important beneficial effects. An alternative suggestion is that play may have only minor benefits, which nonetheless outweigh its minor costs.