Climate change is forecasted to generate a range of evolutionary changes and plastic responses. One important aspect of avian responses to climate change is how weather conditions may change nestling growth and development. Early life growth is sensitive to environmental effects and can potentially have long-lasting effects on adult phenotypes and fitness. A detailed understanding of both how and when weather conditions affect the entire growth trajectory of a nestling may help predict population changes in phenotypes and demography under climate change. This review covers three main topics on the impacts of weather variation (air temperature, rainfall, wind speed, solar radiation) on nestling growth. Firstly, we highlight why understanding the effects of weather on nestling growth might be important in understanding adaptation to, and population persistence in, environments altered by climate change. Secondly, we review the documented effects of weather variation on nestling growth curves. We investigate both altricial and precocial species, but we find a limited number of studies on precocial species in the wild. Increasing temperatures and rainfall have mixed effects on nestling growth, while increasing windspeeds tend to have negative impacts on the growth rate of open cup nesting species. Thirdly, we discuss how weather variation might affect the evolution of nestling growth traits and suggest that more estimates of the inheritance of and selection acting on growth traits in natural settings are needed to make evolutionary predictions. We suggest that predictions will be improved by considering concurrently changing selection pressures like urbanization. The importance of adaptive plastic or evolutionary changes in growth may depend on where a species or population is located geographically and the species’ life-history. Detailed characterization of the effects of weather on growth patterns will help answer whether variation in avian growth frequently plays a role in adaption to climate change.

Phenological adjustments are an important aspect of a population's response to climate change. Changes in phenology can occur through either individual plasticity or evolutionary change within populations. Few studies have investigated both these processes in Arctic environments. Using 42 years of individual and pedigree data, we evaluated the contribution of plasticity and evolution to variation in breeding phenology at a colony of a high Arctic sea‐ice obligate seabird, Mandt's black guillemot (Cepphus grylle mandtii). Mean clutch initiation (first egg in a clutch) advanced 7.8 days, and both environmental (snowmelt) and demographic (years of breeding experience) factors varied among years. Earlier phenology was associated with earlier snowmelt and experienced mothers. Females advanced phenology at different rates as they aged but at similar rates in response to variation in snowmelt. Heritability of clutch initiation was negligible, and there was no evidence of evolution contributing to phenological changes. Earlier laying was associated with increased annual number of fledglings and annual adult survival at the individual level suggesting that the phenological changes are adaptive and are driven by phenotypic plasticity, but not genetic responses. We propose that species with a constrained breeding season (like many Arctic species) may have a limited ability beyond existing plasticity to respond to changing environmental conditions. A free Plain Language Summary can be found within the Supporting Information of this article.

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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 multidecadal 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 icecover 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.