With respect to the development of behavioural criteria to assess substrate quality in relation to foraging behaviour we suggest to observe the frequency of foraging behaviour, as in literature it has been suggested that this isrelated to substrate preference to perform this behaviour (Petherick and Duncan, 1989; Petherick et al., 1990; Matthews et al., 1995). In addition we suggest to observe foraging behaviour when it will most frequently occur and might not be associated with dustbathing, i.e. at the end of the light period.