The authors thank all the volunteers who have participated in BBS and BCT, and the survey organisers. BBS is funded by a partnership of BTO, JNCC and RSPB. The authors also thank Philip Briggs and Becky Wilson for providing BCT data and advice, and Niki Newton and Niall Moore for comments on earlier drafts. The authors are grateful to an anonymous reviewer and Guillaume Latombe for their helpful comments and feedback.

UK animals and plants are surveyed annually by a wide range of long-term citizen science monitoring schemes, which are designed to detect species’ range, status and population trend. Here we explore whether these data are suitable for detection of ecological impacts of invasive species on native species. While expert horizon scans and risk assessments can identify those non-native species that are likely to turn invasive from ecological knowledge, it would be valuable to monitor such impacts in practice. Monitoring scheme data may support such evaluations. We consider the utility of monitoring data in this context via a series of case studies examining the detectability of impacts of Ring-necked Parakeet, Grey Squirrel and Reeves’ Muntjac on native birds and bats that are potentially vulnerable to their impacts. The results show that monitoring scheme data have the potential to provide novel insight informing the evaluation of invasive effects in a range of contexts, adding to current evidence bases, which typically rely upon ecological principles and evidence from small-scale studies. We found a combination of results supporting the expectation of invasive impacts and those not finding such effects. The latter may partly reflect limitations in data quality, such as issues of co-location of data, sample size, adequately detailed identification of at-risk habitats or locations, and likelihood of incompleteness of data on non-natives. We discuss options to enhance monitoring to support enhanced analyses in the future, but analyses of the data can already provide evidence to assist with the determination of invasive impacts now.