When do you scratch that itch? The relative impact of different factors on scratching depends on the selection of time scale and timing.

Abstract

In their interesting article, Duboscq et al . [1] used behavioural data to examine equitably a range of hypotheses on the factors that may cause scratching variations in their wild group of Japanese macaque ( Macaca fuscata fuscata ). They concluded that the animals scratched ‘primarily because of an immune/stimulus itch, possibly triggered by ectoparasite bites/movements’ [1, pp. 1–2] but did not exclude that other factors may have a secondary role. In this Commentary we explain why, in our opinion, the definition of the primary and secondary role of different factors, even within the same group and period, is not absolute but rather time scale and timing dependent. Among other types, stressors can be acute if they have rapid onset and/or short course or chronic if they extend over a prolonged period of time. The response to different types of stressors (e.g. threatening incidents, uncomfortable weather, ectoparasites) also reflects this difference [2,3]. The authors put forth different hypotheses on self-directed behaviours related to the effect that parasitological (presence of ectoparasites), environmental (temperature and humidity/rainfall) and social factors (e.g. aggression, proximity with higher ranking individuals, etc.) have in affecting the rates of self-directed behaviours, including scratching. Such hypotheses are presented as alternative in the first part of the Introduction [1, p. 2] and in the Method section [1, p. 8], …