Abstract
Climate change is altering species' traits across the globe. To predict future trait changes and understand the consequences of those changes, we need to know the environmental drivers of phenotypic change. In the present study, we use multi‐decadal long datasets to determine periods of within‐year environmental variation that predict growth of three seabird species. We evaluate whether these periods changed over time and use them to predict future growth under climate change. We find that predictions of trait change could be improved by considering that 1) the timing of environmental factors used to predict traits (predictive‐environmental features) can change over time, and 2) the type of predictive‐environmental features can change over time. We find evidence of changes in the timing of environmental predictors in all populations studied and evidence for a change in the type of predictor in the studied Arctic murre population. Environmental models of growth predict that warming conditions will decrease growth rates and bird body sizes in two species (black‐legged kittiwake Rissa tridactyla and glaucous‐winged gull Larus Larus glaucescens ), but not the third (thick‐billed murre Uria lomvia ). Consequently, climate change is likely to decrease fledging rates in the gulls and kittiwakes. Further, we find that sea ice‐cover historically predicted murre chick growth well, but no longer does – instead air temperature is now a better predictor of murre growth. Our study highlights a need to investigate whether environmental determinants of trait variation commonly shift in a changing climate and whether such changes have implications for adaptation to novel environments.