Summary
Surveillance monitoring is important for detecting variations in species populations in response to natural and anthropogenic environmental changes. For seabirds this typically involves species-specific monitoring at breeding colonies. It is rare that available resources allow all species to be monitored in an area, resulting in gaps in monitoring programs. Here we assess how natural history observations can provide multi-species community-level information on seabird abundance at Macquarie Island. In 2017–2018 we completed 201 land-based surveys of seabirds in inshore waters and a further 137 surveys in 2022–2023. These are compared against a baseline of 391 surveys from 2002–2003. We found that community composition and seasonal variation in relative abundance in the 2017–2018 and 2022–2023 seasons was similar to the baseline surveys, recording 41 of 43 species observed in the baseline. Land-based observations provide evidence of inter-annual variation in diversity and abundance of non-breeding seabirds visiting inshore waters around Macquarie Island, and of increases in breeding petrels responding to invasive species eradication by 2014. Surveys were less reliable for detecting changes in penguin abundance and prions, diving-petrels and storm-petrels. Nocturnal spotlight surveys led to the discovery of the first colonies of Common Diving-petrels on the mainland of Macquarie Island and circumstantial evidence for recolonisation by storm-petrels. The methods documented here provide information relevant to marine spatial planning and management, and for monitoring regional environmental trends. These surveys are a useful supplement to established on-island monitoring.