With its focus on wetlands, the Ramsar Convention provides the clearest global agreement helping the conservation of migratory waterbirds. Two specific criteria (5 and 6) support the scientific basis for sites to achieve Ramsar recognition based on waterbird counts, while criterion 4, on species and ecological communities, also plays a role. Other international conventions and agreements follow these criteria. We identify several reasons why the listing thus established can only “catch” the absolute minimum wetland network for the conservation of migratory waterbirds. We argue that individual tracking and modern observational tools allow to better delineate the areas needed to effectively give migratory waterbird populations full life cycle protection. The sophisticated techniques to measure population characteristics now available should be used to modernize the guidance for the application of Criteria 4 and 6 of the Ramsar Convention for waterbirds, based on (i) time spent in a site throughout migration; (ii) critical (“untouchable”) sites; (iii) robustness of designated site network including buffer areas; (iv) full life cycle information—including early life phases; and (v) refuges used on-and-off during migration in emergency situations. In these enhanced ways, migratory waterbirds can enact their roles as effective sentinels of the ecological state of the world.