Observer error in counts of macropod scats

Abstract

The accuracy of faecal pellet, or scat, count data can be reduced by observer error. Two experiments were carried out to determine what proportion of Bennett’s wallaby (Macropus rufogriseus) and Tasmanian pademelon (Thylogale billardierii) scats were misidentified by observers and what proportion of scats were overlooked during counts. Observers did not always correctly identify the species from which scats originated. For each species, this affected estimates of the proportion of scats that were present. Observers still made errors even when they did not attempt to make identifications for any scats that they felt were not distinct in form. On average, there was no significant difference in the proportion of scats that were misidentified by inexperienced and experienced observers. Between 3% and 12% of scats were overlooked during standard counts. The probability of overlooking a scat was positively related to vegetation height and negatively related to vegetation cover.