Background Important Bird Areas (IBAs) are sites that are essential to ensure the long-term viability of bird populations, particularly of those species that are of conservation concern. BirdLife International’s IBA inventories are used, amongst others, to analyse whether the EU’s current SPA network is adequate or not. Whereas the terrestrial breeding colonies of marine birds are generally well protected, the definition of marine SPAs at sea has represented a gap in the overall Natura 2000 network. Levels of quantitative data on bird populations and their distribution often decrease with increasing distance from shore. Objectives The project aimed to prepare a detailed inventory, using objective methodological criteria, to determine marine IBAs for 5 seabird species (in two cases representing the totality of the EU population) listed in Annex I of the Birds Directive that live in Portuguese marine waters. Nine more non-priority species (most of them representing very high percentages of the total EU populations) were also targeted by the project, which worked closely in co-ordination with a similar LIFE project covering Spanish territorial waters. Results The project’s main objectives were achieved and resulted in defining key criteria for marine IBAs in Portuguese waters supporting populations of Pterodroma feae, Bulweria bulwerii, Puffinus assimilis, Oceanodroma castro, Sterna dougallii and Calonectris diomedea borealis. Outcomes from the project work provided a model methodology for defining future marine IBAs, and the approach has now been adopted by members of BirdLife International as part of a global standard. This has been applied in countries such as Greece, Malta, the Baltic Countries, Argentina, Peru, USA, South Africa and New Zealand. The process started with an initial pilot methodology for defining marine IBAs that was prepared on the basis of expert advice during an international seminar organised by the project. This first prototype model was then further fine-tuned during consultation with the Spanish counterpart project (LIFE04 NAT/ES/000049). Stakeholder participation was noted as one of the main success factors for the project which brought together information, advice and experience from all essential partners. These included institutions that allowed the LIFE team access to boats and planes for monitoring sea birds and collecting data. Crucial information was also made available and sourced from existing records held by different marine, conservation and other bodies, such as those providing satellite imagery to help the LIFE team determine important environmental parameters about marine habitats. Various sea-bird tracking systems were tested and applied during the project. Innovation was demonstrated through the introduction of new and lighter data-loggers which made useful contributions to the project’s bird census work. Overall results led to IBA criteria being defined for Portuguese marine areas and these allowed the identification of four IBAs around the Portuguese mainland, two IBAs around Madeira, eleven IBAs around the Azores and and 9 other areas were classified outside the Portuguese EEZ (Exclusive Economic Zone). Confirmation of the IBA status for all of these areas is being used to help put in place formal SPA designations under the Birds Directive 79/409/EEC for sites within the EU territory. Information gained during the LIFE project is also expected to be used during development of dedicated management plans for the sea bird SPAs. A collection of high quality dissemination and guidance materials were also produced and are available from the project’s website. Long term sustainability is anticipated as the project’s institutional memory has been mainstreamed within BirdLife International. The project was awarded 1st place in 2008 with the Banco Espírito Santo - Biodiversity prize, created with the aim of rewarding and supporting projects and initiatives for research, conservation and management of biological diversity in Portugal. Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).