The Scottish Government has set a target of 100% of Scottish demand for electricity to be met by renewable sources by 2020. Offshore renewables have the potential to make a significant contribution to achieving this target. However, the Scottish Government has a duty to ensure that offshore renewable developments (ORDs) are achieved in a sustainable manner, by protecting habitats and species from adverse impacts. ORDs may negatively affect seabirds, in particular due to collisions with turbine blades, displacement to less favourable habitats and barrier effects to movement. Displacement and barrier effects are 'sub-lethal effects', whereby individuals birds are not killed instantaneously by an interaction with the wind farm, but their behaviour is affected in the short term, which may have knock on effects on energetic budgets and, in turn, demographic rates such as survival and productivity. A key potential process linking sub-lethal effects of ORDs and demography is the relationship between adult body condition at the end of the breeding season and survival probability over the following winter. However, our understanding of this relationship is limited. This project, led by UK Centre for Ecology & Hydrology (UKCEH) and funded by the Scottish Government and Scottish Natural Heritage, used data on mass, body size, timing of breeding and recapture/resighting histories to estimate the relationship between mass at the end of breeding season and over-wintering survival probability for four key species in the Forth and Tay region: kittiwake, puffin, common guillemot and razorbill. There was evidence for a positive relationship between end-of-breeding season body mass and the survival of puffins with less evidence of an effect in kittiwakes, guillemots and razorbills. This information will help reduce uncertainty in how the impacts of offshore renewables on seabirds are assessed. This research is part of the Scottish Marine Energy Research Programme (ScotMER).