This report presents a summary of existing evidence, and potential research opportunities, to improve the estimates of population abundance and trends, demographic parameters and at-sea distribution and behaviour for Manx shearwater (Puffinus puffinus) and European storm-petrel (Hydrobates pelagicus). This work has been undertaken on behalf of the Offshore Wind Strategic Monitoring and Research Forum (OWSMRF). OWSMRF is an industry-led collaborative forum that aims to identify and develop research to fill critical knowledge gaps in our understanding of the impact of offshore wind development on the marine environment. OWSMRF stakeholders identified baseline data for Procellariiformes as the priority need for improving understanding of offshore windfarm environmental impacts, with the focus on Manx shearwater and European storm-petrel. Improving understanding of population, demographic and distribution parameters were identified as the key knowledge gaps in this area. JNCC has collaborated with experts in this field to provide a summary of potential research which might help to reduce uncertainty in these estimates. This report provides a summary of existing relevant research and evidence, and research opportunities that have been identified to help reduce uncertainty. This report follows on from the Pilot Year Knowledge Gaps (KG1, KG2 and KG3), hence these research opportunities (ROs) are numbered from four.