Using repeat citizen science surveys of koalas to assess their population trend in the north-west of New South Wales: scale matters.

Scale matters when assessing population trends. Whereas traditional field-based ecological surveys are generally restricted to small temporal and spatial scales, community (citizen science) surveys allow wider consideration of population trends. We used repeat community surveys (completed in 2006 and 2015) to assess population change in koalas (Phascolarctos cinereus) across an area of 36 900 km² in the north-west of New South Wales. In both community surveys we asked respondents to record the location of their koala sightings as well as those of eight other common species. We further asked respondents about their perceptions of population change. Through three different measures (likelihood of koala occurrence, number of koalas observed per respondent, and the perception of population change), we found that koala numbers were declining across the region during the study period. The timing and broad and consistent geographic spread of the decline suggests that broad-scale environmental factors, such as weather, are important drivers of this change. This information will allow managers to place conservation efforts into an appropriate spatial context. While such information sourced from the community can provide critical information on threatened species, including the koala, this study highlights the limits of such information. [ABSTRACT FROM AUTHOR]