This dataset contains information on the parental behaviour, diet, condition and demography of common guillemots on the Isle of May, south-east Scotland. Annual data are available for 1982 to 2019 inclusive. These data are part of the Isle of May long-term study to assess population trends of seabirds under environmental change (IMLOTS https://www.ceh.ac.uk/our-science/projects/isle-may-long-term-study). Full details about this dataset can be found at https://doi.org/10.5285/f7676346-a67e-4fdf-9d30-e79ad2585195

[THIS DATASET HAS BEEN WITHDRAWN]. This dataset contains calculated return rates for five seabird species from representative colonies on the Isle of May, off the East coast of Scotland. Annual return rates are measured as the number of individually colour marked individuals seen in any one year that were also observed in the previous year for the Atlantic puffin (Fratercula arctica), common guillemot (Uria aalge), razorbill (Alca torda), European shag (Phalacrocorax aristotelis) and black-legged kittiwake (Rissa tridactyla). Not every individual is seen in any one year and the data set does not take into account those missed in any previous years hence these data are not to be treated as survival estimates. The Isle of May long-term study (IMLOTS) aims to identify the impact of environmental change on seabirds and their associated ecosystems. Understanding the mechanisms underlying variation in seabird population size requires a thorough knowledge of demographic parameters, namely birth rates, death rates, immigration and emigration. The effects of environmental change are likely to be different according to which demographic parameter or life history stage is being considered. This complexity means that only long-term monitoring, such as that carried out on the Isle of May, will allow us to understand the functioning of bird populations and their responses to environmental change. Full details about this dataset can be found at https://doi.org/10.5285/53251b3c-6c79-4aeb-a0de-fc63b9350cc1