Play as Indicator of Habitat Quality: A Field Study of Langur Monkeys ( Presbytis entellus )

The ecology and social behavior of two male bands of Hanuman langurs ( Presbytis entellus ) of similar size and age‐class composition were studied over 18 mo in Rajasthan, Northwest India. Play behaviour was tested as a reflection of environmental conditions. One of the bands lived in a poor habitat where food and water was often scarce, the other in a rich habitat with relatively abundant resources. For example, the proportion of fruit eaten was much higher for the rich‐habitat monkeys (RHM), whereas more than half of the diet of the poor‐habitat monkeys (PHM) consisted of leaves. The frequency of play‐fighting and locomotor‐rotational play correlated negatively with the amount of leaves eaten, probably because they are low in energy. Consequently, play rates for the RHM were not only 6–7 times higher than for the PHM, but play also lasted significantly longer. Play rates among PHM were reduced to zero during adverse environmental conditions but showed a dramatic increase when more plant food became available as a result of monsoon rains. The data provide considerable support for the hypothesis that play is a sensitive indicator of habitat quality.