Camera trap-derived detection rates as relative abundance indices: an empirical test for wild ungulates

Species detection rates achieved through motion-activated cameras have been adopted as relative abundance indices (RAIs) to monitor mammal populations. Yet, group size often is not taken into account by this metric, therefore biases may arise when gregarious species are involved. By considering 3 sympatric ungulate species inhabiting a protected area, between 2019-2021, we compared two RAIs obtained by camera-traps with independent density estimates derived through faecal counts. The RAI incorporating group size (1) showed a stronger linear correlation to density and (2) was the only one correctly ranking interspecific differences in abundance. For the two most Statistical inference for assessing and monitoring atural resources and biodiversity 5 abundant study species, the precision of both RAIs was acceptable, in terms of practical management value (CVs ≤ 25%), albeit it resulted lower for the least abundant one. Generally, our findings support the use of camera trapping-based RAIs as a promising tool to monitor ungulate populations, and that adjusting for group size would improve such metrics.