Do you see what I see? Variation in detection, identification and enumeration of mammals during transect surveys

Effective monitoring, management and conservation of wildlife axiomatically depend on accurate data but causes of variation, including inter-observer variation, are rarely explicitly quantified. Here, under controlled conditions, we demonstrate considerable variation in detection, identification and enumeration of (theoretically) readily-identifiable African mammals at a reserve with a known species assemblage. Detection: 97.8% of sightings were missed by ≥1 observer; frequency of detection was affected by observer ID, detection distance, visibility, and animal group size. Identification: just 3/14 species were identified consistently at all sightings. Enumeration: lack of consensus for 60.5% of sightings; consensus likelihood was affected by visibility and group size