Integrating systematic and targeted scat collection approaches to estimate the abundance of a culturally significant threatened species on Indigenous lands

Estimating the abundance of threatened species can be extremely difficult. This is particularly true in remote regions, where surveys are often expensive and subject to logistical challenges. Where threatened species occur on Indigenous lands, collaborative work between Indigenous people and ecologists who share an interest in the conservation and management of these species may resolve some of these challenges while also meeting additional local objectives. Here, we show the value of integrating two on-ground methods for non-invasive genetic sampling of scat to estimate the abundance of the greater bilby (Macrotis lagotis), a species highly significant to Indigenous people of central Australia that is threatened with extinction. We compared two on-ground methods: (1) systematic surveys, designed to be repeatable, stratified, and standardized, and (2) targeted surveys, which focused on areas where bilby sign was present and involved a more flexible and intuitive search technique undertaken collaboratively with local Indigenous people and informed by their knowledge and skills. We compared different combinations of the two methods and different sampling intensities to explore how they affected modeled estimates of bilby abundance, derived by combining information on individual bilby identities (from DNA extracted from scat) with spatially explicit capture–recapture modeling. We found that combining targeted methods for scat collection with systematic sampling provided the best modeled estimates of bilby abundance and improved modeled estimates for lower overall effort than increasing systematic sampling. This approach also allowed for the inclusion of diverse knowledges and approaches to detecting species (scat) presence. By weaving multiple approaches to find and identify bilby scat, we show how collaborative knowledge-sharing practices can also deliver multiple benefits to Indigenous and science partners.