Monitoring wildlife abundance through track surveys: A capture-mark-recapture inspired approach to assess track detection by certified trackers in the Kalahari, Botswana

Abstract

The surveying of animal tracks is a cost-effective wildlife monitoring technique in conservation, provided the substrate is suitable for tracks to imprint and observers are skilled enough to detect and identify them. However, as with every method quantifying population abundance, it can be biased if track detectability is not accounted for. Track detectability has two components: probability p1ˆ for an animal movement path to intersect with the sampling unit at least once and probability p2ˆ of track detection. Here, we measured p2ˆ, often overlooked, and tested to what extent it is affected by observers and sampling conditions, by applying a capture-mark-recapture approach to a driven track survey of 12 wildlife species in the Kalahari, Botswana. We also characterized and quantified disagreements between pairs of observers on the identification and ageing of tracks. Except for fresh (≤24 old) tracks being slightly more detectable (p2ˆ= 0.77 vs 0.61) and reliably identified (probability of agreement in species identification = 0.92 vs 0.87) than older tracks, we demonstrated that p2ˆ is high and most importantly largely constant across sampling conditions and highly skilled observer pairs. Species identification mismatches between observer pairs were rare (8% for fresh tracks) and limited to specific couples of close species, materializing into confusion rather than directional bias. Where p1ˆ can be accounted for in the derivation of population abundance from track counts (e.g. Formozov–Malyshev–Pereleshin formula), our results relative to p2ˆ validate the use of track surveys for wildlife monitoring in the Kalahari. Our conclusion is potentially applicable to a large range of environments across the globe, especially where observer skills are present among local communities, and conservation can benefit both wildlife and people, fostering their coexistence.