Assessing the state of New Zealand's garden birds from national to local scales.
Better biodiversity indicators are needed to address information gaps, describe trends accurately and robustly and be useful for decisionmakers. Citizen science's potential to help address these challenges often goes unrealized, despite promises by organizers to deliver such information. This paper addresses these challenges by demonstrating the powerful utility of citizen science results for improving our knowledge of the state of New Zealand's garden birds, from the national to the local scale. For 14 species and three annual assessments, we: (a) calculate changes in bird counts over the medium to short term (over 10 and 5 years, respectively); (b) use an alert system to identify trends of interest or concern and collate the assessments in an online interactive tool; and (c) apply the results to address management questions. Seven species have declined nationally in gardens in the medium term, but the population trends of six of these have improved in the short term (the declines of three have been reversed). For Otago, as a regional example, a wider range of medium-term alerts was initially raised, and positive short-term changes were also more evident. Performance differed across Otago's districts: positive increases were muted in Dunedin City, while Waitaki had the highest number of increasing species and Central Otago more species rapidly increasing. For 54 neighbourhoods managed by Predator Free Dunedin, as a local example, the baseline medium-term assessment detected rapid declines in two species, moderate to shallow declines in five species and increases in three species. Based on these findings, managers could improve benefits for biodiversity by using: (a) trends, to direct and evaluate policy investments; (b) benchmarks, to provide social incentives; and (c) targets, to give management purpose and direction. Our case study highlights how citizen science can address biodiversity information gaps and make powerful management contributions at scale by delivering metrics that are robust and comparable across time and space, showing decisionmakers how to readily access and interpret information of interest, building trust and value and highlighting how spatially hierarchical assessments can facilitate multiple end-user benefits.